Watering the sun corridor : managing choices in Arizona's megapolitan area

              Watering the
Sun Corridor
Managing Choices
in Arizona’s
Megapolitan Area
Managing Choices in Arizona’s Megapolitan Area
©2011 by the Arizona Board of Regents for and on behalf of Arizona State University and its Morrison Institute for Public Policy.
Cover Illustration ©2011 Michael Austin c/o theispot.com.
August 2011
Grady Gammage, Jr., Senior Research Fellow
Review Committee Members and Contributors
Sponsored by
Printing generously provided by SRP.
Watering the
Sun Corridor
Tom Buschatzke, City of Phoenix
Peter Culp, Squire, Sanders & Dempsey
Charlie Ester, Salt River Project
Sandra Fabritz-Whitney, Arizona Department of Water Resources
Patricia Gober, Decision Center for a Desert City, ASU
Jay Hicks, RSP Architects
Jim Holway, Sonoran Institute and Lincoln Institute of Land Policy
Sharon Megdal, Water Resource Research Center, UA
Pam Nagel, Arizona Department of Water Resources
Ray Quay, Decision Center for a Desert City, ASU
Terri Sue Rossi, Central Arizona Project
David Snider, Pinal County
John Sullivan, Salt River Project
Jeff Williamson, Arizona Zoological Society
Monica Stigler, Policy Analyst
David Daugherty, Director of Research
Susan Clark-Johnson, Executive Director
William Hart, Senior Policy Analyst
4 | Wat e r i n g t h e S u n C o r r i d o r
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 5
Introduction............................................. 7
	
I. The Sun Corridor................................ 8
Megapolitan Redux............................................8
What Happened to the Growth?....................... 10
Challenges of Geography and Time Frame....... 11
10 Things Residents of the Sun Corridor
Should Understand About Water . . . . . . . . . . . . 12
II. Sources of Water
for the Sun Corridor.......................... 13
Three Concepts: Supply,
Stationarity, and Variability.........................13
The Water Sources......................................13
Rain................................................................ 13
The Salt and Verde Rivers................................ 14
Other Surface Water......................................... 14
Groundwater................................................... 15
Colorado River Water....................................... 16
The Need for Better Numbers on the Colorado .  .  . . 16
Summary of Existing Sun Corridor Supplies.... 17
Climate Change..........................................17
Future Water Supplies.................................17
A Cautionary Note for Sun Corridor Water Planners . . . 18
III. Managing a Desert Water Supply:
From Variable to Reliable................... 19
Salt River Project........................................20
Central Arizona Project...............................20
The Future of ADWR .  .  .  .  .  .  .  .  .  .  .  .   . 22
Managing Groundwater..............................22
Reclaimed Water.........................................24
Conclusions on Supply and Reliability.........25
IV. Demand: Where Does the Water Go? .26
Urban Water Use........................................26
Residential....................................................... 27
Pima and the Politics of Water .  .  .  .  .  .  .  .  . . 28
Commercial/Industrial Uses............................. 29
Agriculture..................................................29
Pinal Perspective: Life in Transition: Agriculture,
Depletion, and Urbanization .  .  .  .  .  .  .  .  .  . 30
Price and Conservation...............................31
The Natural Environment...........................32
V. The Dilemma of the Sun Corridor:
How Should We Choose to Live?....... 33
Final Word............................................. 36
References............................................. 37
Watering the
Sun Corridor
6 | Wat e r i n g t h e S u n C o r r i d o r
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 7
Running out of water must be among the oldest of human fears.
Today, this ancient dread still lingers in the rich green croplands and
sprawling new housing developments of the American Southwest.
Life is good in these warm, sunny, roomy places. But life there also
brings the reminder of relentless and inescapable challenge. The
challenge of water. The fear of running dry.
Arizona’s Sun Corridor—the Central Arizona Urban Region including
Phoenix and Tucson—is one of these places. In the summer of 2010,
residents read in The Arizona Republic that their region was among
the most threatened in the U.S. from global warming.1 A study for
the Natural Resources Defense Council (NRDC) found the Sun
Corridor at “extreme risk” because of a likely widening gap between
precipitation and water demand.2 A few months later The New York
Times announced that “Water Use in the Southwest Heads for Day
of Reckoning,” highlighting the dropping water level of Lake Mead.3
In October, the Times summarized a study by an organization called
Ceres about the risk to municipal bonds of water and electric utilities.4
The view that large populations should not settle in places of little
rainfall sounds reasonable, yet it is clearly at odds with the choices
made by millions of migrants to the Southwest over the past hun-dred
years. In response to their arrival, water in this region has been
pumped, dammed, moved, hoarded, litigated, and fought over to the
point that it has come to define the American West—“Beyond the
Hundredth Meridian.5”
Some insist that Phoenix and Tucson should never have been built.
Others assure us with equal certainty that there is plenty of water if
managed carefully. Both, it seems, cannot be right.
“What about the water?” was one of the questions Morrison Institute
for Public Policy asked in its 2008 study, Megapolitan: Arizona’s
Sun Corridor. That report looked at the potential growth of the Sun
Corridor as Tucson and Phoenix merge into one continuous area
for economic and demographic purposes.
The clearest conclusion of Megapolitan was that no “Sun Corridor-wide”
thinking was taking place. Metro Phoenix and metro Tucson
are consistently regarded as utterly separate places—separate
statistically, culturally, politically, and economically. One significant
goal of the report was to foster “Corridor wide” thinking about issues.
The challenge of water supply and use is the best place to start
this kind of regional thinking. The three core counties of the Sun
Corridor—Maricopa, Pinal, and Pima—are already bound together by
the Central Arizona Project and the limitations of the Groundwater
Management Act.
With its brief review of the water situation in urban Arizona, Mega-politan
left a number of questions unanswered:
• Are population projections for the Sun Corridor still meaningful
in light of the current economic downturn?
• How many people can be supported by the Sun Corridor’s
water supplies?
• What happens if the conventional assumptions about water
availability prove inaccurate?
• How should the impact of climate change be assessed?
• How would lifestyles have to change by dramatically
decreased water use?
• Does more efficient water reuse stretch existing supply?
• What water supplies are available for the future?
This report will consider questions like these in more detail in order to
examine the Sun Corridor’s water future. This topic has received less
sophisticated public discussion than might be expected in a desert
state. Arizona’s professional water managers feel they are relatively
well prepared for the future and would like to be left alone to do their
job. Elected officials and economic-development professionals have
sometimes avoided discussing water for fear of reinforcing a negative
view of Arizona. Public campaigns about water conservation—by
brushing our teeth differently or shutting off public fountains—leave
many residents worried that Arizona faces an immediate shortage.
The result of these different viewpoints has often left the public con-fused:
Is there a current crisis or not? Why do we keep encouraging
growth if there is no water? For the most part, as long as water
comes out of the tap, there is not a widespread discussion of where
our water supply comes from, how much there is, how it is used, and
what will happen in the future. Watering the Sun Corridor seeks to
contribute to this understanding, and to a more open and informed
conversation about the relationship of water and future growth.
Introduction
8 | Wat e r i n g t h e S u n C o r r i d o r
Megapolitan Redux
For generations, Arizonans have talked about the potential merger of
Phoenix and Tucson into a single urban area. The expectation was that
the two would blend together seamlessly, much the way Phoenix and
Mesa did, or like the continuous metropolis now lining the nation’s
East Coast. This has not happened. It probably will never happen,
due to some of the realities Western cities face, such as the Indian
reservations and public lands that lie between Phoenix and Tucson.
More recently, researchers have concluded that an actual physical
merger may not be as significant as an economic one. The real ques-tion,
they say, is what constitutes a single functioning economy.
It was in this context that scholars at the Metropolitan Institute at
Virginia Tech took up the “more than metro” banner while trying to
determine where the next hundred million U.S. residents might live.
Their conclusion was that most growth would be in 20 “megapoli-tan”
areas that together would account for roughly 60% of the U.S.
population living in 10% of its land area. Virginia Tech’s megas reflect
areas that by 2040 are expected to have the U.S. Census Bureau’s
“combined statistical area” designation. The main criterion for this
category is economic interdependence among two or more metro-politan
areas as shown by overlapping commuting patterns. The
working definition is when two or more adjacent metropolitan counties
have an “employment interchange measure” of at least 15%. Elec-tronic
commuting is obviously becoming more prevalent by the day.
But urban areas are necessarily defined by geographic proximity, so
the “employment interchange factor” of overlapping commuting is
the best current thinking on a reasonable means of defining the limits
of a “megapolitan area.”
The Sun Corridor
Michigan Corridor
Lake Front
New England
Mid-Atlantic
Chesapeake
South Florida
Texas Gulf
Central Florida
Texas Corridor
Metroplex
Sun Corridor
Southern
California
Puget Sound
Carolina Piedmont
Southern Piedmont
Front Range
Steel Corridor
Ohio Valley
Northern
California
Williamette
Valley
A Megapolitan Nation is Taking Shape
Source: Metropolitan Institute at Virginia Tech Alexandria.
I
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 9
In its 2008 report, Megapolitan: Arizona’s Sun Corridor, Morrison
Institute applied this methodology to the Phoenix-Tucson area and
concluded that by 2030 the Sun Corridor would include five Arizona
counties: Yavapai, Maricopa, Pinal, Pima and Santa Cruz.
By 2030, the report projected nearly 8 million people living in a 32,000
square-mile region, an 82% increase over the 2000 population.
The report’s principal purpose was to provoke more regional thinking
about the future of urban Arizona. For too long, Phoenix and Tucson
have competed with each other, not realizing that their real competi-tors
are other urban areas in the U.S. and the world. By beginning to
cooperate in analyzing demographic and economic trends, Tucson
and Phoenix may be able to set aside this historic rivalry and begin to
think about their shared identity in an increasingly global economy.6
Megapolitan identified two critical issues related to the environ-mental
sustainability of the Sun Corridor: water resources and the
tradeoff between population growth and quality of life. Both of these
concerns focus on resource limitations, an issue that animates much
of the current discussion about sustainability and the future of the
planet.7 Without massive human intervention to move water and air-condition
buildings, Arizona’s urban growth would have stopped far
short of its current size.
2005 2000 Projected 2030 Projected
Regions and Areas Anchor Metros Population Square Miles Population Population Increase % Change
Northeast 51,601,118 62,612 49,948,064 62,427,070 12,479,006 25.0
New England Boston/Providence 8,276,116 12,320 8,133,219 9,873,668 1,740,449 21.4
Mid-Atlantic New York/Philadelphia 33,527,905 31,027 32,656,309 39,072,196 6,415,887 1 9.6
Chesapeake Washington/Baltimore/Richmond 9,797,097 19,265 9,158,536 13,481,206 4,322,670 47.2
Great Lakes 34,267,189 68,992 33,641,220 39,536,775 5,895,555 17.5
Steel Corridor Cleveland/Pittsburgh 7,067,896 16,320 7,140,287 7,434,689 294,402 4.1
Ohio Valley Cincinnati/Columbus 5,344,052 15,256 5,198,100 6,374,776 1,176,676 22.6
Michigan Corridor Detroit 8,969,861 19,313 8,835,742 10,070,142 1,234,400 14.0
Lakefront Chicago/Milwaukee 12,885,380 18,103 12,467,091 15,657,168 3,190,077 25.6
Piedmont 13,953,787 47,226 12,633,926 19,096,474 6,462,548 51.2
Carolina Piedmont Charlotte/Raleigh 7,012,769 26,175 6,460,338 9,431,809 2,971,471 46.0
Southern Piedmont Atlanta 6,941,018 21,051 6,173,588 9,664,665 3,491,077 56.5
Florida 13,823,188 26,189 12,474,423 20,312,554 7,838,131 62.8
Central Florida Tampa/Orlando 7,851,525 18,126 6,975,772 11,352,506 4,376,734 62.7
South Florida Miami 5,971,663 8,063 5,498,651 8,960,048 3,461,397 62.9
Texas Triangle 18,187,772 70,842 16,525,203 25,598,697 9,073,494 54.9
Texas Gulf Houston 6,247,170 20,801 5,699,704 8,535,961 2,836,257 49.8
Texas Corridor San Antonio/Austin 3,965,018 16,690 3,573,621 5,870,470 2,296,849 64.3
Metroplex Dallas-Fort Worth/Oklahoma City 7,975,584 33,351 7,251,878 11,192,266 3,940,388 54.3
Front Range Denver 3,880,126 20,880 3,582,688 5,594,523 2,011,835 56.2
Sun Corridor Phoenix/Tucson 4,988,564 31,906 4,295,516 7,839,873 3,544,357 82.5
Cascadia 7,350,438 35,746 6,901,160 9,927,217 3,026,057 43.8
Puget Sound Seattle 4,106,956 14,628 3,892,016 5,556,154 1,664,138 42.8
Willamette Valley Portland 3,243,482 21,118 3,009,144 4,371,063 1,361,919 45.3
Northern California Bay Area/Sacramento 11,288,313 24,644 10,788,599 15,057,719 4,269,120 39.6
Southern California Los Angeles/San Diego 21,720,656 49,301 20,326,831 27,796,900 7,470,069 36.7
Megapolitan Total 181,061,151 438,338 171,117,630 233,187,802 62,070,172 36.3
U.S. Total (lower 48 states) 296,410,404 3,007,400 282,193,477 378,302,736 96,109,259 34.1
Megaregions are shown in bold. Anchor Metros rank in the top 50 U.S. Metropolitan Areas.
Source: Metropolitan Institute at Virginia Tech, U.S. Bureau of the Census, ESRI and Woods & Poole Economics, Inc. Morrison Institute for Public Policy, ASU.
Mega Places are Found Across the U.S. from East to West and North to South
10 | Wat e r i n g t h e S u n C o r r i d o r
What Happened to the Growth?
The 2008 Sun Corridor report was written as the scope of the
national economic collapse was emerging. But population projec-tions
for Arizona and the Sun Corridor were based on “boom time”
numbers, still reflecting the assumption that the state’s growth would
always outstrip even optimistic projections. Then the magnitude of
the economic bust became clear. From 2005 to 2010, the prices
of homes in Metro Phoenix, for example, fell by almost 50%8. Arizona
as a state went from creating 121,000 jobs between October 2005
and October 2006 to losing 183,000 jobs in 20099. The Sun
Corridor’s traditionally homebuilding-based economy saw housing
construction plummet.
In light of the realities of the 2008 economic collapse, Morrison
Institute commissioned Marshall Vest, director of the Economic and
Business Research Center at the University of Arizona’s Eller College
of Management, to revisit the population projections. This is a tricky
task. The 2010 census numbers had not been released when Vest
did his projections. Even in normal economic times, Arizona’s popu-lation
is unsettled, dynamic, and transient. It is clear, however, that
population growth has dramatically slowed. But whether the trend
line has changed slope, or just suffered a blip, is not entirely clear.
Vest’s 2008 projections for Maricopa, Pima, and Pinal counties called
for 10.1 million residents in 2040 as the “most likely” population pro-jection.
The “low” scenario was 8.9 million. The new projection is for
a “most likely” 9.0 million—virtually identical to the old “low” number.
Vest concludes that overall population growth will ultimately return to
the Sun Corridor at about a 2% annual rate from 2015 to 2040. Net
migration—people moving into the Sun Corridor minus those moving
out—will return to an “average” of 80,000 per year by 2015. In March
2011, census data was released showing that from 2000 to 2010
Arizona’s population grew by 25%, but housing supply increased by
30%. Housing stats have tended to be viewed as a proxy for popula-tion
growth, leading in this decade to an overestimate. Phoenix, which
had touted itself as the fifth largest city in the country, fell back below
Philadelphia when the numbers were counted.
Despite the slowdown, the projection of a 9 million person Sun
Corridor by 2040 remains the most likely possibility.
-50%
-25%
0%
25%
50%
‘86 ‘87 ‘88 ‘89 ‘90 ‘91 ‘92 ‘93 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘04 ‘05 ‘06 ‘07 ‘08
Arizona
Maricopa
Source: Arizona Indicators, 2009, Morrison Institute for Public Policy, ASU.
HOUSING UNITS AUTHORIZED, PERCENT CHANGE from prior year
9 million person Sun Corridor by 2040
remains most likely Population projection
0
2
4
6
8
10
12
2008
“Most Likely”
2008
“Low”
2011
“Most Likely”
9.0
Million
8.9
Million
10.1
Million
Source: Morrison Institute for Public Policy, ASU.
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 11
Challenges of Geography
and Time Frame
Like Vest’s population projections, this report will focus on the three
big counties at the heart of urban Arizona: Maricopa, Pima, and
Pinal. The original Sun Corridor report included Santa Cruz and
Yavapai, and both of those counties are likely to fit the megapolitan’s
employment-interchange factor in the near future. However, given the
current growth of central Arizona, its three principal counties pose
the biggest challenge. Maricopa, Pima and Pinal are also the coun-ties
with the best relevant statistical data and with locations in the
Central Arizona Project service area. Indeed, the CAP is the closest
thing there is to a Sun Corridor-wide institution. In this report, the
term “Sun Corridor” will generally refer to the more focused three-county
area.
Is there enough water for the Sun Corridor to continue to grow?
To answer that question, we will focus primarily on the three counties
as a single unit. Questions of allocation of water within the Corridor
among competing areas and uses are obviously of huge importance in
shaping urban Arizona.
Knowledgeable “Water Buffaloes” (as they often call themselves)
are likely to find this report’s overview simplistic, as it avoids the
complexity of issues in different parts of the Corridor. They will also
argue that it ignores legal constraints that prevent all water from
being equal. These are valid concerns—some water is usable only in
certain locations, or only for certain purposes, or only by a particular
party or only after decades of negotiation.
The clearest example is the Salt River Project (SRP). SRP, one of the
two big suppliers of water to the region, is legally limited to deliver-ing
to an area referred to as “on project,” which covers only a portion
of the Phoenix Metro area, and therefore only a fraction of the Sun
Corridor. Limiting the size of SRP’s irrigable area was a deliberate
step taken in the early twentieth century to assure adequate water
supplies. Due to these early efforts, and consistent defense of the
limits, this area has the most robust water supplies in all of Arizona.
By aggregating all of the water supplies together and viewing the three-county
“Corridor” as a whole, this report significantly understates the
intra-region challenges which will arise. Will people move to living at
higher densities in the water-rich areas? Will water supplies migrate to
less water-rich areas? Will tension arise between have and have-nots?
How will long-distance infrastructure systems be financed? These
internal equities will be sorted out over coming decades.
The appropriate time frame for analysis is another major consider-ation.
Most analysis of the Sun Corridor’s water situation has tended
to look out to about 2030. Up to that point, known supplies seem
generally adequate to most observers. Beyond that point, popula-tion
projections are extremely speculative, as are assumptions about
lifestyle, commuting patterns, industrial and economic development,
climate change, and virtually any other variable.
Many urban areas—perhaps most in the arid West—do not even look
as far as 2030 in planning water supply. Urban Arizona has been
able to feel responsible, maybe even proud, for its willingness to plan
decades into the future.
Today it is important to look beyond 2030, despite how difficult projec-tions
become. The stress from climate change alone probably makes
that horizon insufficient. Between now and 2030 every assumption
will likely be challenged and changed—including the classic formula-tion
of “predict and plan” that underlies water management. We now
need to derive multiple scenarios, not just a “most likely” alternative,
and will need to constantly adapt to new conditions.
MOHAVE
COCONINO
NAVAJO APACHE
GREENLEE
GRAHAM
PINAL
PIMA
MARICOPA
YUMA
SANTA
CRUZ
COCHISE
YAVAPAI
LA PAZ
Phoenix
GILA
Tucson
Casa
Grande
Nogales
Prescott
Sierra Vista
Five-County Area Three-County Area
Arizona’s Megapolitan: The Sun Corridor
Source: Morrison Institute for Public Policy, ASU.
12 | Wat e r i n g t h e S u n C o r r i d o r
1. Rainfall in the Sun Corridor has little to do with water supply.
Water is brought to this desert from the mountains, where it
rains and snows a lot more. Rainfall does directly impact demand
for water use for landscaping.
2. The renewable water supplies to the Sun Corridor provide “on
average” 2.5-3 million acre feet (an acre foot is 325,851 gal-lons)
of water which could theoretically support a population
of 8-10 million people. But “average” in the context of water
supply does not mean “reliable.” Water supply in an arid region
is highly variable, which is why water management has been
so important.
3. The Sun Corridor’s plumbing systems include reservoirs in
Arizona, bigger reservoirs on the Colorado River and ground-water
banking. Together, these can typically store 4 to 5 years’
worth of urban Arizona’s water demands.
4. Climate change will probably increase variability of supply, and
may reduce the “average” number by as much as 15%. One
bright spot is that our watering systems are designed to handle
high variability.
5. More than half of Sun Corridor water is still used to grow crops.
Agricultural use has provided a buffer during droughts, when
water for farming can be cut back to protect urban use.
6. Groundwater is subject to far more regulation in urban Arizona
than in most states. We have purposefully put significant
amounts of water back underground for the last decade. Even
so, the long-term goal of “safe yield” is a challenge to achieve
and sustain.
7. Per capita use of water has been declining since the 1980s.
The Phoenix area uses much more water for landscaping than
Tucson. This reflects historical and climate differences in the
two cities. But both urban areas have been consistently reduc-ing
consumption.
8. Reuse of urban water will be an important means of stretching
water supplies in the future. Cities in the metro Phoenix area
are among world leaders in reusing effluent, both for landscaping
and for cooling water at the Palo Verde Generating Station.
9. 2.4 million acre feet of average annual water supply appears to
be a reasonable estimate for planning. At the current rates of
consumption, 2.4 million acre feet of annual water could sup-port
about 9.5 million residents in the Sun Corridor. That level
includes no commercial agriculture.
10. The Sun Corridor won’t run out of water, but it faces serious
challenges about how to strike the right balance between pop-ulation
growth and lifestyle.
10 Things Residents
of the Sun Corridor Should
Understand About Water
Recent national media reports echo a number of popular misconceptions about Arizona’s water and water future. In brief,
here are 10 things every Sun Corridor resident should understand:
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 13
Three Concepts: Supply,
Stationarity, and Variability
Supply. There are almost as many ways of defining water supply
as there are reports written on the subject. Sometimes it is thought
of as being the amount of rain that falls within a geographic area.
By this measure, the Sun Corridor long ago outgrew its “water
supply.” Some places treat lakes as water supply. If you are sitting
on the shore of Lake Michigan, the availability of that vast body of
fresh water would seem to resolve any questions about water for
Chicago’s future. In Arizona, major lakes are really reservoirs, man-made
impoundments of water. They are not limitless, or natural, and
are designed to go up and down. In this sense they are not really
“supply,” but rather a management device to store water in times of
plenty for use in times of need.
Groundwater presents another conundrum. Groundwater is pumped
from below the earth’s surface, having percolated there over millennia.
Most of urban Arizona has existed in a state of overdraft—using
groundwater in excess of the amount naturally recharged every year.
Some reports consider effluent reuse a potential water supply
(generally, a significantly unused water supply) for future needs. But
effluent does not represent new water; rather, its use is a manage-ment
technique to make existing water supplies go further. Similarly,
conservation does not represent a new water supply, but rather a
form of “demand” management to stretch available water.
In this report, we will define the Sun Corridor’s water supply as
physical water inputs. These include rain, surface water that can
be transported and made available, and the amount of pumped
groundwater that is naturally replaced every year. Everything else—
lakes, effluent, artificial groundwater recharge, conservation—will
be treated as management techniques.
Stationarity and Variability. Water managers have long
operated under an assumption of “stationarity.” This means that
natural systems operate within a fixed range. Based on historical data
about rainfall, river flows, temperature and so on, reasonable predic-tions
about system behavior can be made. The stationarity principle
includes such concepts as the 50- or 100-year flood event and
the “standard record drought.” Based on stationarity, flood control
systems have been designed, water rights allocated and reservoirs
built. The notion that the past helps to predict and plan for the future
is deeply embedded in water management culture and technology.
In the arid climate of central Arizona, stationarity includes a very high
degree of variability. Sometimes rivers are dry and sometimes they
are at flood. This is the main difference between Arizona and many
other, wetter, parts of the U.S. In places where it rains a lot more,
the stationarity assumption has a much narrower range of variability.
In Arizona, we are used to, and have built our systems upon, wild
swings in conditions. But more recent thinking has challenged even
that highly variable stationarity assumption. One obvious example is
the potential “over allocation” of the Colorado River. When the cases,
statutes, and compacts divided up the Colorado River among Western
states in the 1920s and 1930s, it was assumed that on average the
river would flow at about 17½ million acre feet10 per year. But analysis
of tree ring records now suggests that the 17½ million figure was
inaccurate. The actual average annual flow of the Colorado may be
only 12-15 million acre feet or less.11
The Water Sources
Rain
It does not rain much in the Sun Corridor. The average annual rainfall
at several points throughout the Corridor is shown in the chart below.
Average annual rainfall in inches
Source: Federal Research Division, Library of Congress, Country Studies-Arizona Weather.
Throughout the Sun Corridor, the average is probably about 8-9
inches per year. Analysts looking at the sustainability of places like
the Sun Corridor tend to focus on the balance between rainfall and
water use within a geographic area. This is the formulation used in
the 2010 Tetra Tech report Climate Change, Water, and Risk: Current
Sources of Water for the Sun Corridor
13.3
7.9
8.7
8.0
9.5
12.9 12.5
New River Phoenix Chandler Maricopa Casa Grande Marana Tucson
II
14 | Wat e r i n g t h e S u n C o r r i d o r
Water Demands are Not Sustainable, commissioned by the Natural
Resources Defense Council (NRDC). That report looks at each
county in the United States and analyzes how much water is used
in that county compared to how much rain falls in that county.
The report then goes on to add some assumptions about the impact
of climate change on the differential between “use” and “supply,”
defined as rainfall. By this metric, Maricopa County may be among
the most challenged places in the United States from climate change.
The reality is that Maricopa County’s water use already far exceeds
annual rainfall. Any urban area is by definition a concentration of people
who draw upon a larger area of resources for support. Urban areas
consume many commodities from a larger geographic base. In the
arid West, this includes water.
In the Sun Corridor, like most large metro areas, the average annual
rainfall has little to do with the actual water supply serving the area.
Rainfall levels are more dramatically felt on the “demand” side of
the equation: In times of drought we need more water delivered
for landscape and irrigation. However, in this report we will ignore
rainfall within the Corridor itself as a source of water supply. Rather,
rainfall will be built into the calculus in two ways. First, to the extent
that rainfall replenishes groundwater aquifers on an annual basis,
we will consider the amount of natural groundwater recharge avail-able
to the watering systems. Second, some amount of annual
rainfall is captured by the surface water flows that are managed
within the Sun Corridor. We will therefore analyze water supply in
terms of groundwater and surface water supplies and not add input
for other rain sources.
The Salt and Verde Rivers
The Sun Corridor got its start as an urban area when the Hohokam
began settling on the banks of the Salt River. The Salt, as it flows
through Phoenix, has already merged with its principal tributaries, the
Verde River and Tonto Creek. Well west of the Phoenix metropolitan
area, it flows into the Gila River, which ultimately reaches the Colo-rado.
The flow of the Salt River is highly variable. Its water comes
from the mountains of central and eastern Arizona, a watershed of
about 13,000 square miles. The watershed is fed by both rainwater
and snowmelt. The highly variable runoff in the Salt River, Tonto Creek,
and Verde River watershed is shown by the graph below for the period
from 1913 through 2008. During that 100-year period, flows ranged
from less than 300,000 acre feet to more than 4,200,000.
The average combined flow during this period was 1,199,000 acre
feet. The highly variable nature of this flow may have been part of
what ultimately doomed the Hohokam civilization. Building a society
based on an average flow with this degree of variability is very risky
without storage to “normalize” the flow.
Based on historical stationarity and variability assumptions, how-ever,
it seems reasonable to assume that the Salt and Verde system
delivers on average approximately 800,000 acre feet each year to
the Sun Corridor.
Other Surface Water
One of the least thought-about pieces of the Sun Corridor’s water
supply is the potential availability of other surface water sources.
0
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
‘13 ‘18 ‘23 ‘28 ‘33 ‘38 ‘43 ‘48 ‘53 ‘58 ‘63 ‘68 ‘73 ‘78 ‘83 ‘88 ‘93 ‘98 ‘03 ‘08
Source: Salt River Project.
Salt River, Tonto Creek, and Verde River Combined Annual Inflow, In Acre feet 1913-2008
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 15
These resources, like all surface water flow in the desert Southwest,
are extremely volatile. Variability goes beyond even that of the Salt
River system because many of these sources are ephemeral washes,
which often have no flow at all. This extreme variability means most
of these sources would not be appropriate candidates for dams,
reservoirs, or other intensive human management. Furthermore,
many of these sources have environmental benefits in creating the
part-time riparian environments so critical to the life of the Sonoran
Desert. Many, if not all, of these flows also disappear into the ground,
thereby recharging aquifers.
From a variety of sources, a conservative estimate of these other
surface water supplies emerges:
• Phoenix Active Management Area (AMA) Within the
Phoenix AMA, surface water not counted within the Salt and
Verde system includes the Agua Fria River, New River, the
Hassayampa River, Skunk Creek, Centennial Wash, Cave
Creek, Queen Creek, and the Indian Bend Wash. These
are estimated to produce around 50,000 acre feet in mean
annual flow.12
• Tucson AMa In the Tucson AMA, additional surface water
resources include the Santa Cruz River, Sonoita, Tanque Verde,
and Rincon Creeks, the Canada del Oro, Pintano, Sabino,
Rillito, Aravaica, Brawley, and Altar Washes. These may total
around 50,000 acre feet of mean annual flow.
• Pinal AMa The largest potential additional water supply to
the Sun Corridor is the upper Gila River, before it joins with
the Salt. The river is currently diverted at the Ashhurst-Hayden
Dam. From 1930 to 1986, diversions averaged 230,000 acre
feet per year. Kohlhoff and Roberts13 indicate that as much as
110,000 acre feet of upper Gila River water exists that might
theoretically be available for urban uses. Virtually all of this
water is currently dedicated to agriculture in Graham and
Greenlee counties. Pre-development flows on the Gila River
into the Pinal AMA are estimated to have been as high as
500,000 acre feet per year.14 This suggests that somewhere
between 100,000-200,000 acre feet might be available for
the Sun Corridor from the upper Gila, though using this water
for urban growth would be very politically controversial.
In the aggregate, other surface water supplies available to the Sun
Corridor are probably in the total range of 200,000-300,000 acre feet
per year. For simplicity’s sake, we will estimate these at 250,000 af/yr.
Groundwater
Groundwater use in the Sun Corridor began with the Spanish and
Anglo-American settlements. Some of the earliest wells were drilled
in Tucson. Water was abundant there when the U.S. Army established
Fort Lowell in 1873. The area had a system of canals that brought
water from the river, windmills that pumped groundwater from nearly
35 feet below, and storage tanks sufficient to supply water to all
of the Fort’s major buildings. Several additional wells were installed
in the area by the early 1890s.15 Significant groundwater use in
the Sun Corridor did not occur until the widespread adoption of the
turbine pump after the Second World War. There are now more than
50,000 wells in the Sun Corridor.16
The groundwater supplies in the Sun Corridor have been estimated by
Arizona Department of Water Resources (ADWR) down to a depth
of 1,000 feet at approximately 180 million acre feet.
Phoenix AMA 80 million acre feet
Pinal AMA 35 million acre feet
Tucson AMA 65 million acre feet
TOTAL 180 million acre feet
This estimate is not especially reliable, however, because the science
of groundwater measurement is not particularly well understood.
Fully “dewatering” aquifers causes severe negative consequences
such as subsidence, fissuring, and degraded water quality. In the
three-county Sun Corridor area, approximately 1.6 million acre feet
(MAF) of groundwater were withdrawn for all purposes in 2006. At
the 2006 rate of withdrawal, and based on the estimated 180 MAF
of groundwater available, existing groundwater would be exhausted
in about 112 years if no recharge took place. However, if we treat
groundwater the same as surface water from a sustainability stand-point,
the only safe level of groundwater withdrawal would be that
equal to the annual natural and incidental recharge. DWR estimates
this number for the three AMAs to be about 260,000 acre feet.17
The Sun Corridor has thousands of miles of infrastructure serving commercial agriculture,
such as this irrigation headgate in Marana.
16 | Wat e r i n g t h e S u n C o r r i d o r
Colorado River Water
The Colorado River does not flow anywhere near Arizona’s Sun
Corridor, yet it represents a relatively sustainable source of water
for it. In fact, over 30 million people in seven Western states18 and
over 3 million acres of land—producing some 15% of the nation’s
crops and about 13% of its livestock—rely on Colorado River water.
Fourteen million acre feet of Colorado River water is used in the
United States and Mexico each year.
Bringing Colorado River water to the Sun Corridor was the dream of
generations of Arizonans. It became reality when the Central Arizona
Project canal started delivering water to central Arizona in 1985.19
Through a long series of Congressional acts, interstate compacts and
court decrees, Arizona has won the right to 2.8 million acre feet per
year from the Colorado River. Of that total, uses along the river itself
amount to about 1.2 million acre feet per year; the CAP receives
the balance. The CAP canal was designed to move approximately
1.5 million acre feet to Maricopa, Pinal, and Pima counties. Actual
deliveries since full operation of the canal began are shown in the
chart below. Based on this relatively brief history, 1.5 million acre feet
appears to be a reasonable assumption to use for Colorado River
supplies, at least before delving further into CAP issues.
CAP Deliveries by end user
in volume of Acre feet, 1985-2011
* Forecasted.
Source: Central Arizona Project.
The Need
for Better Numbers
on the Colorado
One of the most critical pieces of research needed for planning
Arizona’s water future is an assessment of the probable long-term
water supply from the Colorado River. The original assumption
used to allocate the flow among the seven basin states and
Mexico is universally acknowledged to have been unrealistic
even when it was made, and the potential challenges of climate
change may well throw the river even further into a condition of
“over allocation.”
A multi-state cooperative effort led by the U.S. Bureau of Rec-lamation
is developing a comprehensive new study of Colorado
River supply and demand. The Colorado River Basin Water
Supply and Demand Study is designed to provide a long-term
look at demand and supply among the seven basin states in the
context of historic, observed and future conditions that could be
associated with climate change.
Each of the basin states is working with the Bureau throughout
2011 to refine water supply and demand information. The study
will develop scenarios for water availability based on hydrologic
projections and the projected demands of other Colorado River
users, including the amount of water likely to be available to
central Arizona via the Central Arizona Project. The first interim
report was released in June of 2011. The final report is expected
by the end of 2012.20
This effort may result in the best estimates to date of what the
water future of the Colorado basin states really looks like.
Arizona’s participation in the Basin Supply and Demand study has
been largely the result of an effort by a group of private funders
working with ADWR. For information on the study, or to help fund
its completion, contact ADWR at www.azwater.gov.
The conclusions of the completed study may well prompt
Arizonans to revisit the question of water supply for the future of
the Sun Corridor.
‘85
0
250,000
500,000
750,000
1,000,000
1,250,000
1,500,000
1,750,000
2,000,000
‘87 ‘89 ‘91 ‘93 ‘95 ‘97 ‘99 ‘01 ‘03 ‘05 ‘07 ‘09 ‘11*
Agricultural Indian Municipal & Industrial
Direct Recharge Exchange
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 17
Summary of Existing Sun Corridor Supplies
Based on conventional stationarity (meaning with no adjustment for
climate change) assumptions, the supplies of “sustainable” water
available to the Sun Corridor can be summarized as follows:
Salt/Verde 800,000 Average Af/Yr
Other Surface Water 250,000 Average Af/Yr
Natural Groundwater Recharge 260,000 Average Af/Yr
Colorado River 1,500,000 Af/Yr
TOTAL 2,810,000 Af/Yr
This summary undoubtedly includes some overlap; much of the
“other” surface water, for example, is likely currently viewed as “natural
recharge.” Another caveat: This number is a potentially misleading
average produced by widely varying amounts of rain and runoff. The
best historical data on variability is probably that from the SRP system,
which has varied from 30% to 400% of average. The challenge of
managing this variability is discussed in Section III.
Climate Change
The classic stationarity assumptions made about water supply in
places like the Sun Corridor did not consider the potential effects
of long-term climate change. A 2008 article in Science magazine
declared “Stationarity is dead” because climate change may produce
results well outside of historic ranges.21 Stationarity may indeed be
dead, or merely challenged; underlying assumptions may have to be
changed, or not. In any case, it seems clear that a greater range of
variability has to be assumed in the future.
Some studies suggest that the Colorado River system yield could
be reduced by as much as 30% over the coming decades. A recent
work by the National Oceanic and Atmospheric Administration and
the National Center for Atmospheric Research suggests a range of
decline of 10-20%.22 The most recent Colorado River projection of
the possible impact of climate change suggests a 9% decline in
flow by mid-century.23 There is a tendency to assume that, because
the Sun Corridor is already so hot and dry, “global warming” will
disproportionately negatively impact the area. Certainly if summer-time
temperatures continue to rise, at some point Arizona becomes
a less attractive place to live, regardless of how much water there is.
But on the other hand, the Sun Corridor is better prepared to deal
with highly variable rain and snowfall conditions than most places
on the planet. As noted above, this is the underlying principle upon
which the water supply of the Sun Corridor has been built.
Besides increasing variability, climate change may well reduce the
long-term average amount of available water. If an aggressive 15%
decline in the average Colorado River flow is also applied to the
Sun Corridor’s other water sources, the nearly 2.8 million acre feet
of “average” annual input to the Corridor could drop to 2.4 million.
Arizona occupies a “junior position” for Colorado River water entitle-ment,
which puts it at greater risk. Together, California, Nevada, and
Arizona are entitled to 7.5 million acre feet (MAF) from the Colorado.
The Sun Corridor’s rights—to 1.5 MAF of CAP water—is assigned
the lowest priority position among all these uses.24 Theoretically
then, ignoring storage, a major reduction in Colorado River supply
could severely curtail CAP water deliveries to the Sun Corridor.
Future Water Supplies
for the Sun Corridor
Because of Arizona’s dramatic growth, its historic challenges and
the potential impact of climate change, water managers have begun
analyzing where future Sun Corridor supplies might come from. The
Central Arizona Project has conducted a long-term dialogue, called
“ADD Water,” engaging numerous stakeholders in the region.25
Future supplies were analyzed with regard to physical, legal, and
political constraints, and compared against a series of various con-tractual
and political demands for future supply. Implementation of
any effort to obtain new supplies means a multi-decade effort in the
complex diplomacy of western water.
One analysis of future supplies created “tranches” of future supplies
labeled “highly likely,” “likely,” and “possibly available.”26 One large
potential source—though one with huge political ramifications—
would be moving some Colorado River water from western Arizona
agriculture to the Sun Corridor. There may be 200,000 acre feet
or more available annually. Another potential source is groundwater
imported from places in Arizona that are unlikely to urbanize; there
may be another 200,000 acre feet or more available annually from
such isolated sources. Though, like all groundwater, it is exhaustible,
and its transportation controversial.
The ultimate solution for the arid West is generally assumed to be
de-salinization plants built on the Pacific Ocean. This is usually
touted as a way to bring vast additional supplies to Los Angeles
or San Diego—or even to Las Vegas, which could use more of
California’s Colorado River supplies if California could pull from
the ocean. These cities are more immediately challenged for future
supply than is the Sun Corridor. De-salting the ocean is an expen-sive
proposition. Reverse osmosis, the most commonly considered
technology, uses huge quantities of electricity to force seawater
through a membrane, leaving behind the salt. Costs can run in the
$1,500-$2,000 range for each acre foot produced.27 As technology
improves, the cost of desalted seawater will drop—in some parts of
the world it is now below $1,000/af. As total water supplies grow
scarcer, existing costs will rise. The lines will eventually converge,
reflecting once more that, in the history of the urban West, “water
flows toward money.” But desalted ocean water will not be coming
to the Sun Corridor anytime soon.
A Cautionary Note for
Sun Corridor Water Planners
Ray Quay and Patricia Gober, Decision Center for a Desert City (DCDC), Arizona State University
At first glance, this report’s message about the Sun Corridor water
supply appears positive. But water managers and urban planners
should proceed with caution. That’s because first, climate change
may reduce supplies in the long term; and second, because our
region does not depend upon one big bucket of water, but on many
smaller pails linked to individual water providers. The Sun Corridor
thus confronts two quite distinct futures: Will it emerge as a coop-erative
region in which surpluses are shared and risks from drought
and climate change are more evenly distributed? Or will it succumb
to the challenges posed by an uncertain climate, unsure supplies,
and a concentration of risk in places of rapid growth?
Climate change should be on water planners’ radars, but no easy
answers come from climate models, which are notoriously uncertain
about the impacts of climate change on surface supplies at local
and regional levels. They tend to agree that the future climate will
be warmer, but disagree about future rainfall and runoff conditions.
DCDC’s analysis of the Intergovernmental Panel on Climate
Change’s 2001 model finds an estimated temperature rise for
central Arizona of between 2.4 to 5.6°C, using 2050 greenhouse
gas emissions. These increases, along with widely varying rainfall
estimates, suggest future ranges in runoff for the Salt-Verde water-shed
between 50% and 127% of historical levels. Similar studies
for the Colorado River showed flow ranging between a decrease to
61% and an increase to 118% of historical flows, averaging around
90% of mean flows.
However, recent DCDC work does point to the differing impacts of
shortages on individual providers in Maricopa and Pinal counties.
Some will be able to manage even the most extreme shortages;
others would be seriously challenged by only moderate shortages.
Nor will water-sharing resolve all problems. Another DCDC study
showed that spot shortages can be largely ameliorated through
cooperation during moderately severe climate-change conditions.
But such strategies have little effect under the most extreme sce-narios
because no communities have surpluses to share.
The second critical issue facing the region is the fragmented nature
of water governance—the fact that myriad providers make individual
and generally uncoordinated decisions. The Sun Corridor’s water
budget hardly consists of one big bucket. Instead, there are 285
water providers, ranging from major players to irrigation districts. The
municipalities that rank as the largest of the Phoenix-area providers
supply in excess of 50,000 acre feet annually. At the other end are
providers delivering a few thousand acre feet to outlying communities.
Their vulnerability to future climate change varies enormously
depending upon our supply portfolios, lifestyle and landscaping
preferences, and potential for future growth.
Irreducible uncertainties—about drought-induced water shortages,
regional growth patterns and climate change impacts—suggest that
the future could be far from normal for all parts of the Sun Corridor.
Looking 20 to 40 years ahead, water shortages from long-term
drought could have temporary but significant impacts on the region’s
groundwater supply. In the 40-to-60-year horizon, climate change
could increase temperatures and decrease stream flows, enhance
the length and severity of drought conditions, and boost the intensity
of storms. It’s clear that under these changing conditions the Sun
Corridor faces serious water challenges. These sobering possi-bilities
require us to think seriously about the adequacy of existing
infrastructure, the relevance of operational rules and the sustainability
of projected growth patterns and lifestyles.
The old adage of “predict and plan” worked well when the systems
were stable, time periods were 20 years or less, the impact of being
wrong was not catastrophic, and financial resources were fairly
plentiful. None of these conditions now holds true. New decision-making
strategies that envision and plan for a wide range of futures
are thus needed today more than ever. Individual planning will not do
it. Indeed, the Sun Corridor’s fragmented form of water management
risks creating winners and losers rather than sharing risk and benefit.
Recent studies by the City of Phoenix and the East Valley Water
Forum showed that communities that rely heavily on groundwater
may face significant problems during long-term drought conditions.
The interconnected nature of the groundwater system means that
such communities could in turn jeopardize the water future of neigh-bors
that had planned judiciously for their future. This may or may not
be considered legal, or fair, but it’s clearly not the future Sun Corridor
any of us want.
18 | Wat e r i n g t h e S u n C o r r i d o r
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 19
The Sun Corridor’s challenge has been to create a water supply for
desert cities that is reliable and sustainable. With abundant sunshine
and plenty of arable land, the Sun Corridor attracted its earliest
Native American inhabitants because it was a good place to grow
crops. The Hohokam built an extensive irrigation system in central
Arizona based on the waters of the Salt and Gila Rivers, but their
system lacked a large-scale means of storing water. This meant that
their delivery system was subject to both drought and flood—a fact
that may well have been the ultimate source of their demise. In the late
19th century, Jack Swilling and other early settlers built an irrigation
system atop the Hohokam canals. But until the creation of large-scale
storage by the federal government early in the 20th century,
the variability swings remained a serious challenge.28
Today, three key elements of the Sun Corridor’s water supply are
intensely managed toward a goal of smoothing variability. These are
the surface waters of Central Arizona (managed through the Salt
River Project), the Colorado River (managed by the Central Arizona
Project), and groundwater (managed under the Groundwater
Management Act).
Managing a Desert Water Supply:
From Variable to Reliable
SRP Reservoir System, Salt River Reservoir District, and City Boundaries
Source: Salt River Project.
III
20 | Wat e r i n g t h e S u n C o r r i d o r
The Salt River Project
The Salt River Project is one of the great water-management success
stories of the United States. It also is a notable legacy of the federal
government’s “reclamation” policy to advance settlement of the arid
West by storing and moving water. Landowners in the Salt River
Reservoir District put their land up as collateral in the early 20th
century to build a series of dams. Establishing the reservoir district
and water rights within it helped to ensure the Valley’s water supplies
for more than 100 years. The first of SRP’s storage dams, Theodore
Roosevelt, was the largest in the world at the time.29 Today, SRP
is both a water provider and an electrical utility; it operates eight
dams, 251 groundwater wells, and 1,300 miles of canals and later-als
serving about 250,000 acres. The area was once agricultural, but
is now more than 90% urbanized. SRP water must be used within
the SRP service area, including deliveries to a host of cities. These
deliveries give users with SRP rights robust water portfolios and
management flexibility.
In 2010, SRP’s reservoirs were at 96% of capacity.30 In total, they can
store about 2.3 MAF of water, or about two years’ worth of runoff from
the watershed.31 More than 70% of this is stored in Roosevelt Lake.
The chart below shows SRP surface water deliveries for the period
from 1950 to 2009.
The Salt River Project also controls significant groundwater resources
within its territory. For planning purposes, this groundwater is oper-ated
like another “reservoir” with a current annual maximum delivery
capacity of about 325,000 acre feet, or just over 1/3 of the annual
water demand in the SRP service area.32 Operationally, SRP uses
mainly surface water when the reservoir system is full, thereby enabling
it to store as much water as possible for future use. As storage levels
decrease, groundwater pumping is increased until a productive
runoff season refills the reservoirs. If storage levels continue to
decrease, deliveries by SRP are reduced to save the surface water for
as long as possible. As agriculture in the SRP territory has declined,
so generally has groundwater pumping.33 Balancing deliveries of
water in this way has made the Salt River Project supply very reliable.
During the last 60 years, SRP has been able to deliver a full allocation
of water to its shareholders 93% of the time. In four of the 60 years,
SRP reduced the allocation for two years in a row, during the worst
droughts in the Project’s 100-year history. Deliveries to water users
from SRP’s system have totaled, on average, about 950,000 acre
feet per year.
The Central Arizona Project
The CAP system is also a surface water-delivery system, but on a
scale quite different from SRP’s. The Colorado River serves multiple
states, including some of the fastest-growing and driest urban and
industrial areas in the United States. The futures of these communi-ties
and economies is tied, in whole or part, to water availability from
the Colorado River. Over the next 40 years, the population depen-dent
on the Colorado River could grow by 25 million or more, leading
to an increase in water demand of perhaps 5 million acre feet.
The Central Arizona Project is only one piece of the Colorado River
delivery system, and does not even represent all of Arizona’s demand
on the Colorado. The overall system has truly vast reservoirs, Lake
Powell and Lake Mead, each of which can store about 25 million
acre feet. Theoretically, storage on the Colorado amounts to more
than three years worth of average annual flow. In order to win federal
authorization for the CAP, Arizona had to agree that its CAP alloca-
‘50 ‘60 ‘70 ‘80 ‘90 ‘00 ‘09
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
4,000,000
4,500,000
Total Deliveries Salt, Tonto and Verde Inflows
Source: Salt River Project.
SRP deliveries from completion of Horseshoe Dam through the present
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 21
tion would be the “junior most” priority on the river and, therefore, the
most susceptible to interruption in times of shortage. This concern
has animated much of Arizona’s recent policy in dealing with the
Colorado. While a shortage has never been declared in the lower
basin, negotiations among the basin states have resulted in guide-lines
for shortage sharing among the lower basin states. Shortage
sharing is triggered based on year-end water level elevations in Lake
Mead as indicated below.
Lake Mead’s elevation was approximately 1,092 feet as of January
2011.34 This means that it was only about 41% “full.”35 The pro-longed
drought on the Colorado River has left Lake Powell at about
57% full.36 Recent releases from Powell to Mead will rebalance
the reservoirs, and the large 2010-11 snowfall will rebound both
reservoirs somewhat. The Colorado system has been considered
in drought conditions for over ten years, and yet deliveries have
not been curtailed, demonstrating the intended function of these
huge reservoirs. The contrast between the Colorado system and
the Salt system is an inherent part of the reliability and sustainably
strategy of the Sun Corridor.37 Deriving water from two different
geographic areas (the mountains of central Arizona and the Rockies
in Utah, Colorado, and Wyoming) was long thought to create a more
balanced and sustainable supply. Tree ring data analysis shows a
higher degree of drought correlation between central Arizona and
the Colorado system than was previously thought.38
Colorado River water users, led by the U.S. Bureau of Reclamation,
produce models of the operation of the Colorado in an attempt to
determine the probability of shortage. Recent model runs (August
2010) indicate there is no more than a 20% probability of shortage
in 2012. Current models project that shortages would not impact
CAP municipal and industrial or Native American contractors until
about 2020 and then only under “worst case” conditions.39 Even
with a reduction of 432,000 acre feet, the highest level of
reduction considered in the current shortage sharing guidelines,
CAP would still receive around one million acre feet. Today, CAP’s
long-term (mainly municipal) contractors use just over 800,000
acre feet. “Excess” contractors, including most farmers, use another
nearly 800,000 acre feet of water. So most reductions—even severe
ones—would be absorbed by agriculture.
Despite this huge cushion of agricultural use, however, CAP’s junior
position means that in times of shortage, it would take most of
the first cut—before California agricultural use, before Nevada, and
before Arizona on-river use. While there have been suggestions to
change this system, it remains in place. A decrease in availability on
the Colorado could greatly impact the Sun Corridor.
A highly variable system, the Colorado River is subject to dramatic
change in runoff from year to year. CAP may experience some level
of shortage during the next 20-25 years. While the magnitude and
duration of a shortage cannot be predicted, CAP’s own analysis
suggests that its municipal users are not likely to experience a sig-nificant
reduction in supply during this period. However, a prolonged
shortage would seriously reduce the amount of water available for
agricultural users and limit the ability to bank water for future use.
Year-End Lake-Level Elevation
(Feet above Sea Level) Reduction in Acre-Feet
333,000
	 Arizona’s Share: 320,000
	 CAP’s Estimate Share: 288,000
	 417,000
	 Arizona’s Share: 400,000
	 CAP’s Estimate Share: 360,000
	 500,000
	 Arizona’s Share: 480,000
	 CAP’s Estimate Share: 432,000
	 Secretary Consults with Basin States
Summary of Reductions in Colorado River
for Arizona and CAP
0
5
10
15
20
25
30
‘64 ‘66 ‘68 ‘70 ‘72 ‘74 ‘76 ‘78 ‘80 ‘82 ‘84 ‘86 ‘88 ‘90 ‘92 ‘94 ‘96 ‘98 ‘00 ‘02
Colorado Flows
Salt, Tonto and Verde Flows
‘04 ‘06 ‘08
Source: U.S. Bureau of Land Reclamation, Current Natural Flow Data 1906-2008 and Salt River Project.
Colorado and Salt, Tonto and Verde Flows, in million acre feet
Below 1075 but Above 1050 Feet
Between 1050 and 1025 Feet
Below 1025 Feet
Below 1000 Feet
22 | Wat e r i n g t h e S u n C o r r i d o r
Managing Groundwater
For decades in Arizona, groundwater was simply treated as a resource
available to anyone who wanted to pump it from beneath their land.
Legally, groundwater was thought of as being separate and distinct
from surface water and was largely unregulated. This remains true
today in most of the United States. But excessive and continuous
groundwater pumping raises a number of problems. Groundwater
depth in a place as dry as Arizona is often great enough that drill-ing
is expensive and risky. Excessive and continuous groundwater
pumping can lower the water table; as water is removed, the soil
can collapse and damage buildings and infrastructure. At some point
excessive pumping of groundwater leads to the depletion of a finite
resource that accumulated over hundreds of thousands of years.
Groundwater is in this sense similar to oil.40
In 1980, due to years of pumping for agriculture and to meet increasing
urban demands, the Arizona State Legislature adopted the Ground-water
Management Act (GMA) and created the Arizona Department
of Water Resources (ADWR) to protect groundwater supplies for
the future. The GMA was also insisted upon by the U.S. Secretary
of the Interior before agreeing to fund the Central Arizona Project.
In fact, part of the rationale for the CAP was to replace long-term
groundwater pumping with renewable surface water. The GMA ranks
among the most innovative policy initiatives undertaken by Arizona.
The GMA designated areas of the state where groundwater pump-ing
was heaviest as “Active Management Areas” (AMAs). The Sun
Corridor, as we use the term here, lies within these AMAs. The chart
below shows the change in the rate of groundwater withdrawal for
the three counties since passage of the GMA.
change in the rate of groundwater withdrawal
for the three counties since passage of the GMA,
In acre feet
Source: ADWR.
0
200,000
400,000
600,000
800,000
1,000,000
1,200,000
‘85 ‘90 ‘95 ‘00 ‘05 ‘06
Phoenix AMA
Pinal AMA
Tucson AMA
The Future
of ADWR
Water management is frequently cited as something Arizona has
done exceptionally well. Indeed, water issues have historically been
dealt with by a broad, non-partisan consensus of Arizona leaders
and institutions. But the state’s precarious budget situation has
put that strong legacy in jeopardy.
The Arizona Department of Water Resources was created in
1980 in the Groundwater Management Act. In the 30 years since,
ADWR has:
• quantified and protected groundwater rights
• adopted conservation plans
• facilitated groundwater storage
• ensured that new residential developments have
a 100-year supply
• defended Arizona’s Colorado River rights against
other users
• protected endangered streams and rivers
• acted as the focal point for discussion of state water issues.
Since 2008, ADWR’s budget has been cut by 70%. In 2011,
its budget has dropped below 1984 levels. Full-time-equivalent
employees have declined from more than 235 to 95. Programs
have been completely eliminated; offices outside of Phoenix have
been closed. Some $47 million in funds collected to store water
for future shortages, implement Indian water settlements and
protect remaining streams was “zeroed out” by the Legislature
and shifted to general state operating funds.
Ultimately, a legislative bargain was struck through which cities
agreed to pick up a major share of DWR funding. These costs
will be built into municipal water bills.
Public funds are unquestionably scarce. Still, shrinking ADWR
and potentially jeopardizing our history of careful water manage-ment
do not seem the best way to celebrate Arizona’s centennial.
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 23
In Pima and Maricopa counties, the GMA was intended to reduce
pumping toward a “safe yield” condition and thereby end ground-water
mining. The Pinal AMA, however, was originally designed to
allow groundwater depletion to preserve agriculture for as long as
possible while reserving a supply for future urbanization.
Safe yield represents a balance in groundwater supplies in the
aquifer between what leaves (generally through pumping) and what
is returned to the aquifer (through natural or artificial recharge). The
goal of safe yield has proved to be elusive. As of 2006, 45% of the
three-county supply still comes from groundwater pumping.
While current evaluations indicate that safe yield has been achieved
in the Phoenix AMA, and that the Tucson AMA has come close, long-term
projections indicate that without more aggressive water manage-ment,
the ability to maintain safe yield will not be realized.
Part of this shortfall derives from a water-accounting anomaly:
water being artificially “recharged” back into the aquifer (which is dis-cussed
below) is not counted against withdrawals, but is “banked”
for future use. In addition, because physical delivery of CAP water is
too difficult in many areas, the CAP supply has not always replaced
groundwater pumping in the direct manner that was probably originally
envisioned. But the biggest reason is probably simple economics:
pumping groundwater is cheap. We still live under long-standing
federal policies that provide low-cost electricity for agricultural
pumping, a remnant of the reclamation era.
Arizona continues to be among the most active and innovative
states in groundwater management. One important tool for securing
groundwater supplies in the AMAs has been the requirement that new
developments demonstrate secure physical, legal, and continuous
access to a 100-year assured water supply . This is a stricter standard
than California’s, which requires a 20-year access (and only for large
subdivisions).41 The 100-year supply in Arizona should generally come
from surface water, preserving groundwater for when surface water is
not available. In practice, this provision was designed to push devel-opment
in the Sun Corridor to areas with access to municipal water
based on a municipal system with a CAP contract. Theoretically, this
should have resulted in containing and compacting development in the
Sun Corridor and making it more difficult to develop far outside of
municipal boundaries.42
Since 1993,43 developers have been able to meet the renewable
supply requirement by enrolling in the Central Arizona Groundwater
Replenishment District (CAGRD). This program allows groundwater
to be pumped for a new development as long as it is replaced with
water from the CAP or other non-groundwater supplies through
artificial recharge. This enables development to continue without
investing in expensive water acquisition and transmission facilities or
water treatment plants.
The CAGRD has been criticized as a “shell game” that allows
groundwater pumping in the expectation that replacement water will
be available to be recharged somewhere else in the AMA; but this
recharge could occur so far from the development that in practice it
circumvents the requirement of renewable water availability for de-velopment.
44 At the height of the development boom, the CAGRD
proved much more successful than originally envisioned, with nearly
265,000 lots entitled through this mechanism. The downturn in
development has dramatically slowed enrollment, but it is likely that
either the availability of this mechanism will be curtailed in the future,
or the costs will dramatically increase, or both.
Arizona has also been at the forefront of large-scale institutional
groundwater recharge. Starting in 1986,45 the state began recharging
underground aquifers with available surface water. The initial impetus
was to use the otherwise unused portions of Arizona’s CAP allo-cations
to keep them away from California. In addition, in order to
satisfy California’s thirst, the U.S. Secretary of the Interior in the late
1990s declared a series of “surplus conditions” on the Colorado River
resulting in the release of additional water that Arizona could take
for its own purposes. Because Arizona’s population had not grown
enough at the time to consume even its base CAP allocation, a series
of mechanisms for using extra water were created. Spreading basins
were built in dry riverbeds where water can be poured out onto the
desert, allowing it to percolate back into the aquifers. Another mecha-nism—
indirect recharge—displaces legal and cheap groundwater for
agriculture with surface water. The surface water is used to water crops,
and the un-pumped groundwater is counted as indirectly recharged
surface water which can be recovered in the future.
Since the mid-1990s, the Arizona Water Banking Authority (AWBA)
has been storing excess CAP water to shore up supplies during a
shortage. The AWBA has even banked water on behalf of Nevada.
When Nevada needs that water, it will withdraw directly out of Lake
Mead, and Arizona can pump the banked water to satisfy needs that
would otherwise have been met directly with CAP deliveries.46 These
various mechanisms have resulted in more than 4 million acre feet of
water being put back underground in central and southern Arizona.47
Groundwater banking is ultimately a management technique just like
reservoirs: a means of smoothing out a highly variable water supply.
But it is a less flexible and longer-term solution. Getting the water ex-actly
where and when it’s needed in the future may pose challenges.
But the fact that urban Arizona has managed to save millions of acre
feet of groundwater for future use clearly improves the reliability of
the Sun Corridor water supply.
24 | Wat e r i n g t h e S u n C o r r i d o r
Reclaimed Water
The issue of reusing wastewater from urban households is becoming
increasingly important—but remains a tricky category of water to think
about. Some commentators discuss it as a significant new source
of water “supply” that is more effectively and readily developed than
other new sources.48 But this is really not “new” water. Rather, it is a
management technique for stretching an existing supply.
There are several different categories of wastewater that can be
reclaimed in urban areas: storm water runoff, power plant cooling
water, agricultural return flows, household gray water (dishwashing
or showers), and sewage. Techniques for treating and reusing
effluent are becoming more sophisticated. Some effluent—like city
sewage—is better treated on a large scale, while other types may
be reclaimed by individual households. Additional questions include:
Is the reclaimed water to be used for landscaping? Fiber crop
irrigation? Food crops? Aesthetic purposes like fountains or artificial
lakes? Can the water be reused for body contact? What about for
flushing toilets?
In 2009, Governor Jan Brewer appointed the Arizona Blue Ribbon
Panel on Water Sustainability. That panel reviewed water reuse by
area around the state, and concluded that the percent of treated
wastewater reused or recharged in the Sun Corridor was:
Pinal AMA 58%
Phoenix AMA 49%
Tucson AMA 15%
The Panel also noted that Arizona’s gray water rules have been
referred to throughout the U.S. by gray-water advocates as the “model
to emulate.”
Because so much Sun Corridor water is used for landscaping, the
most readily available reuse is effluent treated to the level that it can
be used on plants and supplant the use of potable water. This approach
became prominent in the Sun Corridor in the 1980s and 90s with the
use of reclaimed effluent on golf courses. Scottsdale and Tucson pio-neered
this use. A large effluent line specifically serving golf course
development has been built in north Scottsdale, and throughout the
city about 12 million gallons per day of reclaimed water is used to
irrigate golf courses. But even this reuse poses some problems. For
example, another source of water must periodically be used to flush
from the soil the salts concentrated in reclaimed water. It is thus
difficult for any landscape use to exist on 100% effluent. A second
problem, particularly for some golf courses, is that the seasonal demand
for water and the seasonal production of reclaimed water do not
always coincide. Snowbirds produce effluent in the wintertime, but
golf courses need most water in the summer.
It is also important to note that there is an inverse relationship between
interior conservation and effluent production. As household plumbing
fixtures become more efficient in conserving water that is initially
used, the per capita amount of effluent produced decreases. With
the advent of ever lower-flush toilet fixtures, waterless urinals and other
appliances, in-home per capita production of available wastewater
has been falling.
As water has become more valuable, an initial concern was owner-ship
and control over effluent. In an Arizona Supreme Court decision,49
the court determined that treated wastewater would be the property
of the entity that treats it, since it is no longer of the same character
as the source water. The court also found that treatment facilities are
not obligated to discharge treated effluent for any downstream user
even if it initially came from surface water.
A recent master’s thesis at ASU, which extensively examined reclaimed
water issues, estimates that the Phoenix AMA in 2006 generated
approximately 315,000 acre feet of effluent.50 This would suggest that
the total Sun Corridor effluent production today may be approaching
500,000 acre feet. The Sun Corridor is one of the nation’s better-performing
urban areas with regard to the reclamation of urban
water. The City of Phoenix asserts that well over 90% of its effluent is
reused. This includes delivery to turf facilities for irrigation contracts
and, most importantly, for cooling at the Palo Verde Nuclear Generating
Station. The multi-city 91st Avenue Treatment Plant delivers annually
about 60,000 acre feet of effluent to Palo Verde.51 Other treated
effluent from the plant is discharged into the Salt riverbed, where it
forms the Tres Rios Riparian Area. In fact, because in Arizona efflu-ent
cannot be discharged into the ocean or another huge body of
water, it is in some ways appropriate to think of all effluent as being
“reused”—as it ultimately winds up recharging underground aquifers.
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 25
Conclusions on
Supply and Reliability
As noted, the most sustainable water supply for the Sun Corridor
is surface water. Because precipitation within the Sun Corridor is
low, most of its surface water supply is imported. Arizona law since
the 1980 Groundwater Management Act has strongly preferred that
urban growth occur based on this surface water supply. However,
the high variability of surface water supplies poses risks. The solution
has been to smooth out the water supply through large-scale
storage. In Section II, we concluded that annual water inputs to the
Sun Corridor total an average of about 2.8 million acre feet. Preliminary
climate-change assumptions currently suggest possibly reducing
that level by 15%, to 2.4 million. But variability makes such “averages”
risky to rely upon. The junior status of CAP rights further exacerbates
that risk.
Storage systems are designed to increase reliability. The SRP system
can theoretically store nearly one full year of the Sun Corridor’s
supply—2.3 million acre feet. Arizona’s “share” of the Colorado River
reservoirs is not separately quantified; but, if full, they theoretically
impound almost 4 years’ worth of lower basin entitlement. So the
aggregate reservoir system serving the Sun Corridor is capable of
storing between five and six years of the “average” annual input.
Artificial groundwater recharge to date adds another 1 ½ years.
Is this enough? Should we save more? Should we be comfortable
with the current low levels on the Colorado but a full SRP system?
Given the watering systems of the Sun Corridor, we typically store
4-5 years’ worth of supply—maybe as much artificial storage as any
place on the planet. Metro Atlanta, in contrast, had less than thirty
days of water supply on hand at one point in 2008.52
The Sun Corridor reservoirs have functioned successfully, and the
public seems to understand the general concept. But Arizonans
are less clear on how to think about the role of groundwater. We
have shifted our thinking from an era which regarded groundwater
as hydrologically separate from surface water which could be used
whenever needed. Today, by contrast, there is a tendency to believe
that groundwater should never be used as a water supply. If reser-voirs
are the “savings,” we should think of recharged groundwater
the same way, though perhaps more like a “certificate of deposit”—
slightly harder to withdraw. In this analogy, prehistoric groundwater
is our “inheritance”—a kind of trust fund that is available in emer-gencies,
but that we would prefer to leave for future generations. In
the face of past assumptions about variability—a storage system of
five years supply or so has been reasonable and sufficient. But in
the face of potentially much greater future challenges from climate
change and altered assumptions, our savings are starting to feel a
bit thin. Looking out to 2060 and beyond, as population and urban
demand increase and harden, the margin becomes troubling.
So does the Sun Corridor have enough water for the future? Does
your family have enough money for the future? The answer to these
questions is the same: it all depends.
Spreading basins, such as the Granite Reef Underground Storage Project above, allow water to
percolate into the soil and are used to recharge the groundwater tables.
26 | Wat e r i n g t h e S u n C o r r i d o r
Urban Water Use
Where does the Sun Corridor’s water go? While there are many
different ways to slice the pie, the most typical one separates water
use into three categories: municipal, agricultural, and industrial. Most
Arizona water still goes to irrigated agriculture.
The “industrial” category includes a range of users like electronic
chip manufacturing plants and electric power generation. In Arizona,
“industrial” also includes some golf courses, because direct ground-water
pumping by a golf course requires an industrial permit. But many
manufacturing and employment-related water uses are not actually
captured by the “industrial” category because these uses are directly
served by municipal water providers. It seems more useful, there-fore,
to group water use into two categories: “urban” (municipal and
industrial) and agricultural (meaning commercial irrigated agriculture).
The urban category represents the Sun Corridor as an emerging
megapolitan region.
Each of the three principal counties in the Sun Corridor has a different
water use profile.
Since the 1980 Groundwater Management Act, the shorthand way
of explaining municipal water use has been in gallons per capita per
day or “GPCD.” GPCD takes the water delivered by a municipal
utility and divides it by the population the utility serves. The chart
to the right shows the GPCD rate as usually compared for the three
central Arizona AMAs.
Based on these typical numbers, each acre foot of non-agricultural
water in the Sun Corridor appears to support about 5 people (4.2 in
the Phoenix AMA; 5.5 in the Tucson AMA in 2008).
Gallons per Capita per Day Rates
for Central Arizona AMAs
Source: ADWR.
The downward trend in GPCD water use in all three AMAs is signifi-cant.
This is in large measure the intended result of the Groundwater
Management Act. More efficient use of water has been achieved
through education, increased water rates, and a variety of regulations
on specific uses.
It is difficult to compare per capita water use from one region to
another. Different cities, states and countries include different uses
in their calculations and a huge difference results simply from the
variation in rainfall in different places. The U.S. Geological Survey
cites the U.S. national average as 150 GPCD, with Vermont the
lowest state at below 100.53 Of urban arid regions, Australia, in the
depths of a drought crisis, dropped residential use from 70 GPCD
to 34 in 2007-08.54 Urban Arizona’s decreased GPCD has been
Demand: Where Does the Water Go?
Agricultural Industrial Urban
Municipal
70%
8%
22% 53% 47% 96%
4%
68% 32%
Source: Arizona Water Atlas, Vol. 8 (2010). Arizona Department of Water Resources.
Water use profiles for Arizona and three counties
Arizona Maricopa Pinal Pima
1985 1990 2000 2008
Phoenix Pinal Tucson
246
228
176
253
219
175
259
220
181
216
192
163
1985 1990 2000 2008
Phoenix Pinal Tucson
347
313
248
352
297
243
344
296
246
272
313
219
IV
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 27
the result of deliberate incremental changes over three decades, not
an immediate response to a crisis. We can expect to see continuing
improvement in these numbers.
There is a tendency to take these per capita numbers and use them
as a proxy for all “urban” water use. So if an acre foot/year supports
about 5 people, 1,000,000 acre feet should support a population of
5,000,000? Not exactly.
In the Sun Corridor, there are non-farming water uses which are not
included in GPCD calculation. These include things like factories and
mining supplied by their own pumps, rather than city water. Untreated
water delivered for flood irrigation of homeowners’ lawns, a feature of
some parts of metro Phoenix within the SRP boundaries, is also left
out. Golf courses with their own water supply are not counted. Dairies,
high water users, are also omitted. These uses should be grouped into
the “urban” category.
These other urban uses cannot simply be inserted into the per capita
numbers and rebalanced. Some of them have little or no relation-ship
to population growth. Copper mining, for example, occurs in
the Sun Corridor because of ore locations. Water use for copper
mining is independent of local population, and fluctuates with global
demand. Sand and gravel mining, on the other hand, is related to
nearby construction, and it does therefore correlate more closely
to increased population. Using untreated water for flood irrigation
of lawns is largely a historic remnant and is likely to decline over
time. While these uses all have different characteristics, the most
convenient shorthand is to treat them as “non GPCD” uses distinct
from commercial agriculture. In 2006, the latest year for which
aggregated figures are available, the non GPCD uses for the three
AMAs totaled about 175,000 acre feet.55
Using the 2008 GPCD numbers and the 2006 non GPCD “urban”
consumption, the Sun Corridor’s urban water uses, including every-thing
but commercial irrigated agriculture, can be approximated.
current Approximate “urban”
water use in the sun corridor
Residential
Tucson is one of the most water conservation conscious communities
in the United States. Per capita water use rates in the Tucson AMA
have long been among the lowest in the arid states. Phoenix has also
made significant progress in reducing its urban water use, though
it remains far more water consumptive than Tucson. The difference
between the two communities is largely historic. Phoenix has always
been a farming town with immediate access to a flowing river that,
while highly variable, generally had a low flow rate nearly four times
that of Tucson’s local natural surface water supply.56 Even though
Phoenix is both drier and hotter than Tucson, it was this difference
that made Phoenix a location for irrigated agriculture.
As Phoenix urbanized, it generally transformed flat, agricultural land
into subdivisions. This made the importation of non-native species
and a Midwestern landscape palette of grass and deciduous trees a
logical choice for early settlers. As the city grew, the Hohokam canal
system became a template for providing agricultural water. The Salt
River Project was the nation’s first use of federal funding for creating
an ever greater capacity for irrigated agriculture. The size and reliability
of that water supply continued to support the urbanization of land in
an “oasis” urban form.
Tucson, by contrast, consciously urbanized as a desert environment
rather than an oasis. Its more meager water supplies meant that agri-culture
was never an important part of its economy. Its milder climate,
higher elevation, and more varied topography gave Tucson a “desert
living” character that Phoenix lacked. The result of these differences
is the dramatically different water consumption of the two cities: It is
all about the landscape. Interior home water use is now approximately
60 gallons per capita per day in both cities. In newer subdivisions,
because of advances in water conservation technology in bathrooms
and kitchens, this number is even lower. It is likely that inside home
water use will continue to decline slowly on a per capita basis.
In the Phoenix metro area, about half of residential water use occurs
in the landscaping outside the home. This ratio used to be higher,
with estimates as high as 60-70%,57 but smaller lots, xeriscaping,
higher water prices, and educational efforts have consistently reduced
the percentage in recent years. New subdivisions use markedly less
outdoor landscaping water than older parts of town. The most recent
City of Phoenix estimates place outdoor use citywide at 46%.58
Some other cities in the metro area are likely higher, because of
larger lots, higher overall GPCD numbers, and older landscape. In
the Tucson AMA, the ratio is significantly lower, with outside use
arguably below 30%.59
On a Sun Corridor wide basis, there is no clear way to estimate
exactly what percentage of residential use is going into outdoor
landscaping, but it is likely to average about 45-50%.
Many Sun Corridor cities have created educational and regulatory
programs to encourage a desert or “xeriscape” landscape palette.
300,000
600,000
900,000
1,200,000
1,500,000
Non-GPCD 175,000af (2006)
GPCD Uses 1,120,000af (2008)
(200 GPCD average x 5,000,000 population)
Total “Urban” Uses 1,295,000af
28 | Wat e r i n g t h e S u n C o r r i d o r
Pima and the Politics of Water
Sharon B. Megdal, Water Resource Research Center, University of Arizona
The adage “local policies reflect local values” is certainly true in
Tucson, where front lawns are rare, xeriscape is common and water
conservation has long been an intense public concern. In truth, of
course, every community within the Sun Corridor is distinct, with
different histories, cultures and local challenges. Yet our destinies are
inextricably, and increasingly, linked. This is why it’s crucial for all of us
to develop an understanding of each others’ resources and needs.
It’s equally crucial that we understand local political and economic
landscapes. Water management, especially in semi-arid regions, can
be a complex and high-stakes affair.
Lines of ownership, authority and jurisdiction are often scrambled.
Tucson Water, for example, serves about 80% of the municipal water
demands, but more than one-third of its customers reside outside
the city limits. These residents do not elect the Mayor and Council,
who set the water rates, nor vote on water bonds or initiatives that
would change the City Charter. Several other public and private
water providers exist in the region. Pima County provides waste-water
treatment for most of the region, but the City owns a large
portion of the treated wastewater in an arrangement unique in
Arizona. Finally, the U.S. Secretary of the Interior controls 28,200
acre feet of the region’s effluent, which it manages for the benefit of
the Tohono O’odham Nation.
Against this complex backdrop, the arrival of CAP water in Tucson
made the early 1990s a turbulent time. Tucson Water had planned
to be the regional provider of CAP water, but this was derailed by
the formation of several new smaller utilities by residents outside the
Tucson city limits as well as by nearby municipalities of Oro Valley
and Marana. Local control of water assets and supply became a
focus of citizen activism. The real trouble came when Tucson Water
first delivered treated CAP water to its customers. The overnight
switch to treated CAP water for over half the utility’s customers was
disastrous. Pipes burst, water was brown, and fish died. In 1995,
city voters approved a citizen-developed initiative that forced Tucson
Water to abandon plans for direct delivery of CAP water after treat-ment.
Instead, a strategy dependent on recharge and recovery has
taken hold, and recharge basins have been built to the northwest
and south of Tucson. In other words, the landscape—literally as well
as politically—sharply changed.
But all was not conflict. Several efforts to think and plan regionally
about water were launched during the 1990s, with mixed outcomes.
A legislatively authorized regional water district was not made per-manent.
The Southern Arizona Water Users Association (SAWUA),
an affiliation of water interests, established itself as a regional voice
for water providers and large water users. The Water Conservation
Alliance of Southern Arizona (Water CASA) formed so that the
smaller utilities could collaborate on water conservation programs.
The northwest area water providers began to collaborate on efforts
to utilize CAP water. The key issue of CAP reliability was resolved in
2010 with a plan based on recharge rather than a surface storage
facility. Yet several other CAP issues still remain unresolved, such
as a pipeline to bring this renewable water supply to the Sahuarita-
Green Valley area.
Effluent remains another unresolved issue. The City of Tucson and
Pima County have had their differences regarding how treated waste-water
should be reclaimed and reused. They agreed to set aside a
pool of effluent for environmental purposes; yet nearly 10 years later
the use of the pool appears undetermined. The city and county also
worked together for three years to develop water and wastewater
recommendations that would benefit the region, including its natural
environment. In addition, the multiple owners of effluent have worked
collaboratively on effluent recharge in the Lower Santa Cruz River.
The people of Pima County realize how critical water management
is for their future and know that they must work together on shaping
that future. Citizen awareness of water scarcity is widespread and
intense, as is residents’ desire for water policies that balance human
and environmental needs. But while Tucson is “different,” this same
need for collaboration among water interests, public decision-makers
and citizens exists throughout the Sun Corridor. Harmonizing the
water policies of the Sun Corridor’s distinct regions will require the
time and effort necessary to acknowledge our differences as well as
recognize our commonalities. Tucson’s experience is showing that,
with patience, persistence and public education, it can be done.
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 29
The results have been significant, if not always as dramatic as
expected. An ASU study concluded that drip irrigation systems
often do not save as much water as anticipated because of their high
maintenance problems, frequent leaks, and the tendency of home-owners
to overwater desert plants.60
Commercial/Industrial Uses
Cities and municipal providers have also sought to encourage con-servation
by commercial and industrial users, and have incorporated
water use into their economic-development policies. Arizona became
a magnet for silicon chip manufacturing in the 1970s because
Motorola and Intel found it a good environment for building clean
rooms and for attracting a skilled workforce. Chip manufacturing
uses large amounts of water, though the industry has promoted
extensive conservation and reuse techniques.
Scottsdale and other Valley cities encouraged construction of golf
courses for another major economic-development activity and “export”
industry—tourism. Over time, water-use regulations have prompted a
significant decrease in the amount of turf planted, the development of
new kinds of turf and the use of recycled wastewater.
Nationally, the most water-intensive industry is arguably electric
power generation, which diverts about 48%61 of the nation’s annual
supply. But this number includes cooling water that flows through
plants and is returned to streams and rivers. In Arizona, only about
5% of the water supply goes to power plants, and much of it is
reclaimed water to begin with.
Mining is a significant industry in Arizona and a significant water
user—about 1% of the state’s general usage and somewhere around
40,000 acre feet in three counties. There are proposals to signifi-cantly
expand mining in the Tucson and Pinal AMAs. Historically,
mining has primarily used groundwater.
Agriculture
Since at least the time of Marc Reisner’s Cadillac Desert 62 it has
been politically expedient to criticize most large-scale irrigated west-ern
farming as wasteful. A recent Stockholm Environment Institute
report63 continues this view, and is especially critical of Arizona’s
situation, which on a statewide basis the authors see as 77% of
water supply going to agriculture, with 54% of that share being used
for high-water/low-value hay production. Reisner’s own bleak vision
predicted that massive confrontations between agricultural and urban
interests would potentially devastate western politics.64
Arizona has been fortunate to avoid such cataclysmic confrontation
because as the Sun Corridor has urbanized, farm land and water
have been converted to subdivisions in the same place: the Sun
Corridor. This land use evolution has seemed natural, logical, market
driven, and relatively sustainable, since houses often use less water
than crops.
Within the Sun Corridor, about 1,800,00065 acre feet of water per
year are still used for irrigated agriculture. Agriculture in Maricopa and
Pinal counties peaked in the late 1980s and has been declining since
then, but more than 95%66 of Pinal County water still goes to farming.
Total number of Acres planted for
all agricultural purposes by County
Source: Morrison Institute for Public Policy, ASU; data from the U.S. Department of
Agriculture, National Agriculture Statistics Service, 2007.
0
100,000
200,000
300,000
400,000
500,000
‘60 ‘65 ‘70 ‘75 ‘80 ‘85 ‘90 ‘95 ‘00 ‘05
Maricopa
Pima
Pinal
Phoenix Tucson
While Phoenix has moved toward a more desert landscape palette, a large percentage of homes still include grass and non-native trees. The houses of Tucson have long embraced
a more indigenous landscape. Tucson Photo Source: Community of Civano, LLC.
30 | Wat e r i n g t h e S u n C o r r i d o r
Pinal Perspective: Life in Transition
Agriculture, Depletion, and Urbanization
David Snider, Pinal County, District 3 Supervisor
One of Arizona’s more enduring items of conventional wisdom has
been that Phoenix and Tucson will grow together just like most
of southern California. Ground Zero for that projected growth is,
of course, Pinal County. The time frame was vague. The concept,
depending on where you lived, was greeted with healthy skepticism
(and mild distaste) or a shrug of inevitability. But Pinal County’s
hyper-growth of the last 10 years has transformed that notion into
a matter of urgent importance.
Pinal has relied on agriculture to act as steward of its aquifers while
both the Arizona State Land Department and the federal government
manage much of its open spaces. The county contains three Active
Management Areas—two with a goal of “safe yield,” and one with a
goal of “planned depletion.” Agriculture still accounts for approxi-mately
25% of the county’s economy and nearly 90% of the Pinal
AMA’s water budget. However, the agricultural portion of this budget
is diminishing as activity in the municipal and industrial sectors
increases. Virtually all of the county’s manufacturing is also located
in the Pinal AMA.
But “planned depletion” does not mean “let agriculture de-water the
AMA to a depth of 1,000 feet”—as many planners may have thought.
The goal is actually: “to allow development of non-irrigation uses and
to preserve existing agricultural economies in the AMA for as long as
feasible, consistent with the necessity to preserve future water sup-plies
for non-irrigation uses.” The AMA’s irrigation districts (excepting
the San Carlos Irrigation District) have been using CAP water for the
most part during the past 20 years. This has mitigated depletion of
the AMA’s aquifers while bolstering groundwater supplies.
The AMA’s water budget includes additional supplies of renewable
water from the conversion of non-Indian ag water rights to Municipal
and Industrial (“M&I”) purposes as well as significant naturally
occurring renewable sources of water. However, the municipal and
industrial sector has relatively small contract amounts of M&I priority
CAP supplies (approximately 15,000 af) at present which, in turn,
presents a significant challenge for Pinal AMA water resource plan-ners.
In addition to pondering the adequacy of water supplies, water
resource and land use planners debate the merits of moving water to
growth, or growth to water.
County officials have been responding to these challenges. County
Supervisors and staff initiated a revision of their Comprehensive
Land Use Plan in 2007, three years earlier than required. A Morrison
Institute study cited Pinal County residents calling overwhelmingly
for open spaces, green and sustainable communities, and balanced
growth and development. As a result, the newly revised plan called
for more serious consideration of water resources as development
projects move through the zoning process. The rules concerning
assured and adequate water supplies for the Pinal AMA were revised
several years ago to promote the movement of growth to water (i.e.,
lands currently used for irrigated agriculture) as opposed to water
moving to growth. And the Pinal County Water Augmentation
Authority is assuming a larger role in the pursuit of additional renew-able
water supplies for M&I uses.
Tribal water settlements have been negotiated and finalized for two of
Pinal County’s four Native American communities: the Ak-Chin Indian
Community and the Gila River Indian Community. Most of the claims
asserted by the Tohono O’odham Nation have also been resolved.
Discussions with the San Carlos Apache Tribe have been ongoing
for some time and show no signs of conclusion. For the most part,
these settlements have allocated significant supplies of Colorado
River water to tribal control and ownership; water leases are rare,
but exist as potential components to Pinal and Arizona short- and
medium-term planning.
County leadership is also working with economic development
organizations to market the county and to recruit manufacturing and
transportation-related prospects. Pinal County is looking forward
to the energy and synergy of the Sun Corridor. We are, however,
determined to create a future that retains the county’s unique iden-tity.
That future will include manufacturing, agriculture, green tourism
and mining—together providing employment in a blended ratio of
county-residents-to-jobs. In other words, residents who live in Pinal
County will be able to work in Pinal County. That future will also
enable residents to appreciate agriculture as a key part of the county’s
economy, its commitment to conservation and to the preservation of
open space, and its respect for its cultural heritage.
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Arizona has no official policy about preserving agriculture; except
in the Pinal AMA where we seek to: “…preserve the agricultural
economy for as long as feasible.” Most Arizonans have assumed
that agriculture in the Sun Corridor would be priced out of busi-ness
as land is converted to subdivisions and water converted to
urban uses. Because of our reliance on elaborate irrigation systems,
Arizona farms have tended to be large, often corporate, and have
generally focused on fiber rather than food. In recent years, agricul-ture
has existed as a kind of holding zone—something to be done
with land until it is urbanized. The common refrain has been that an
acre of houses uses less water than an acre of crops—which is not
entirely accurate as it depends on development density, landscaping
and other amenities.
More significantly, there is a fundamental difference between agricul-tural
and municipal water. Municipal water must be highly reliable. It
must be always available, and cannot be easily reduced. Agricultural
water, on the other hand, may be interrupted if there is a need or a
higher value to which the water can be put. This is not true for long-term
crops like citrus or pecan trees, but is a relatively widespread
practice with cotton, alfalfa and other row crops. In the drought of
the past decade, Phoenix metropolitan residents have not suffered
mandatory cutbacks (unlike Las Vegas or other arid cities) because
agricultural deliveries can be curtailed, preserving water for the
cities.67 As agriculture declines in the Sun Corridor, however, its
availability as a buffer will diminish.68
In the late 1990s, under pressure from the federal government, the
CAP, ADWR, SRP, and others sought to resolve the claims of cen-tral
Arizona’s tribes—principally the Gila River Indian Community—
to Gila River water. The Salt and the Verde rivers are the main
tributaries of the Gila, but their flows have been fully used by SRP’s
shareholders. The only significant unallocated water source available
to satisfy the Gila community’s claims, therefore, was the CAP. Some
653,500 acre feet of water from various sources, including CAP
allocations, was dedicated to the tribe.69 This water will flow to the
375,000-acre reservation lying in the middle of the Sun Corridor
between Phoenix and Tucson.70 This report includes this water in
calculating the Sun Corridor supply, since the Gila River community’s
land is in the Sun Corridor and the water is dedicated to that use.
Absent some new policy intervention, the Gila reservation may well
be the only long-term significant agriculture to remain in the Sun
Corridor. The water can potentially migrate either temporarily or
permanently to urban uses.
Price and Conservation
Conservation is best thought of as demand management. Reducing
per capita consumption stretches existing supplies and allows popu-lation
to increase without finding new supply.71 Three strategies have
traditionally been pursued. The simplest is educating consumers to
use more care in water use inside and outside the home. Phoenix, for
example, has successfully educated existing customers and devel-opers
of new subdivisions about conservation techniques.
The second major conservation technique involves regulations on
water use. Examples include requiring low-flow plumbing fixtures in
new construction, limiting landscaping and restricting artificial lakes.
The Groundwater Management Act has imposed some of these
regulations in the Sun Corridor, such as restricting landscaping in
public rights-of-way and limiting turf on golf courses. Cities have
imposed regulations through their building codes and in individual
zoning cases. Las Vegas has pursued an approach to the extent of
paying residents to remove their lawns.
Sun Corridor cities also use pricing mechanisms—the third ap-proach—
to promote conservation. Water remains a relative bargain
here, even compared to other parts of the U.S. Water is inevitably
becoming more expensive throughout the U.S. But increasing its cost
is politically difficult, and can raise tough questions of social equity.
Municipal water prices are extremely complex, and include huge com-ponents
for infrastructure costs, treatment costs, and maintenance
and delivery. Often “water bills” also include other city services such
as sewage and even garbage collection.
Tucson has been a national leader in aggressive “block pricing.” This
makes a minimum block of water available at relatively low cost. A
single family homeowner pays less than $2 per 1,000 gallons for
the first 11,000 gallons of monthly use—an amount sufficient for use
inside most homes. After that, however, the price nearly quadruples.
Applying Tucson’s four-level pricing structure to Phoenix would
achieve dramatic reductions in use, while also causing dramatic
changes in landscaping.72
This kind of price signal causes permanent behavioral changes, and
reinforces conservation far more dramatically than regulation or educa-tion.
Higher prices are undoubtedly a part of the Sun Corridor’s future.
Typical Monthly Water Bills: Rank Among 50 Largest
U.S. Cities. Rank from Lowest (1) to Highest (50)
3,750 Gallons 7,500 Gallons 15,000 Gallons
Phoenix 21 28 26
Tucson 22 14 49
Albuquerque 12 7 5
Atlanta 49 50 50
Chicago 2 2 2
Denver 5 4 10
Las Vegas 20 8 4
Los Angeles 29 40 40
Seattle 50 49 49
Source: Black and Veatch 2009/2010 50 Largest Cities Water/Wastewater
Rate Survey.
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The comparisons of municipal water bills from U.S. cities reflect
these complexities and a myriad of considerations having little to
do with the actual price of developing water resources. Water is
very expensive in Seattle, for example. But it is not needed there for
landscaping, so per capita consumption is low. In most of the cities
of the arid Southwest, water rates have been kept intentionally low
to protect a lifestyle made possible only by subsidized water—first
for agricultural settlement, and then for urbanization. When the City
of Phoenix sought a 7% increase in January of 2011, it was met with
a howl of protest from the citizenry.
The Natural Environment
In the development of the plumbing systems for the Sun Corridor, in-deed
for most of the Southwest, the place of free flowing streams and
rivers has generally been treated as an afterthought. When we tote up
how water is “used” whatever is left over for nature was historically
regarded as the next source of supply. In the Sun Corridor, water
flowing in a river bed is an unusual circumstance, and in an attitude
inherited from the reclamation era, was long viewed as “wasted.”
Water management decisions greatly impact natural environments
throughout Arizona. Fresh surface water and groundwater are the
foundation of social, cultural and economic well-being. Healthy fresh-water
ecosystems provide clean water, food, and fiber for humans,
as well as energy and habitat for animals and plants. In the long
term, sustainable uses of water resources must acknowledge that
preserving and restoring hydrological systems and natural habitats
accrue multiple economic benefits to local communities through
tourism revenues, enhanced groundwater recharge, water quality
protection, reliable water supplies, improved flood control and storm
water management, increased air quality, moderated ambient tem-peratures,
recreational benefits, and improved public health.
Surely some of the water supply of the Sun Corridor should be
protected and dedicated to the environment. If such a provision is
not made, conversion of the full supply to urban uses will seriously
degrade the quality of life for all those who live here. How this balance
should be struck is one of the central questions of the region’s growth.
But assigning a number of acre feet to preserve in-stream flows and
protect the environment is beyond the scope of this report.73
Salt River
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Many of the national negative views of the Sun Corridor’s water
supply are based on simply analyzing rainfall vs. use and conclud-ing
there’s a big imbalance. This is true of the TetraTech and Ceres
reports cited in the introduction. Sustainlane.com criticizes urban
Arizona’s sustainability because water comes from far away. The
Stockholm Environment Institute looks at all water use, including
commercial agriculture, and concludes that it can’t continue forever
at current levels.
None of these critiques are on point. The population of central Arizona
has outstripped rainfall since the time of the Hohokam. Arizona water
policy is built around preferring imported, and therefore renewable,
surface water. Agricultural use has been steadily, and largely intention-ally,
converting to urban use.
In fact, these critiques are so far off base that many Arizona water
managers have never even bothered to respond. If any response is
made, it’s usually based on the assertion that we have enough water
supply to serve a significantly greater population than currently lives
here—up to 10 or 12 million people.
The simplistic assertion that there is plenty of water for the Sun
Corridor’s future is based on this sort of equation: 3 million acre
feet x 5 persons/acre foot = 15 million people. This is unrealistic.
Even with our reservoirs, groundwater banking and other reliability
mechanisms, we cannot assume that 3 million acre feet is a reliable
number. Any allowance for climate change implies a further reduc-tion
in the reliability of existing systems. And the future presents
an equation in which supply becomes more variable while demand
becomes less variable.
It is also inappropriate to use the GPCD number as a proxy for the full
urban economy of the Sun Corridor (meaning water uses except for
commercial irrigated agriculture). Somewhere between 200-255,000
acre feet are currently being used outside of the GPCD statistic. If we
add agriculture to the “urban” chart shown earlier, the total current
water use picture looks something like the chart which follows.
This chart shows that the Sun Corridor currently uses about 3 million
acre feet every year. The number is in excess of what we concluded
was an “average” sustainable supply. Of course some years are
above average, but consistent use at this level is the result of ground-water
mining. This chart is also a useful graphic demonstration of
the place of agriculture as a historical but declining sector of the
Corridor’s economy. As population increases, irrigated agriculture
will continue to diminish. Agriculture is a rational “optional” use. The
portion of the chart that shows Indian agriculture is likely to grow as
a result of the CAP settlements. Non-Indian agriculture has been on
a long decline as the result of both land and water being urbanized.
Indian agriculture will likely not follow the same trajectory, since the
land is not likely to urbanize with subdivisions.
current Approximate TOtal
water use in the sun corridor
Even if we supposed that all farming—even Indian farming—went
away, the question of what population can be reasonably supported
by existing water supply remains.
Let us take 2.4 million acre feet as the “supply” assumption, as sug-gested
in part II, and freeze the non-GPCD urban uses at their 2006
level of 175,000 acre feet. That would essentially mean that things
like mining, golf courses, and industrial uses will not increase in the
future, unless they do so based on a municipal supply that is captured in
the GPCD numbers. That may not be a completely realistic assumption,
but these uses do not strictly track population growth, so some
assumption is necessary. The remaining supply of 2.2 million acre feet
becomes the “sustainable” base against which varying per capita use
can be considered. This allows us to create a very simplistic matrix of
the theoretically supportable population of the Sun Corridor:
The Dilemma of the Sun Corridor:
How Shall We Choose to Live?
Water Supply 1,800,000af 2,000,000af 2,200,000af
Per Capita Use 	 Approximate Population
200 GPCD 8,182,000 9,100,000 10,000,000
(.22 af/yr)
150 GPCD 10,588,000 11,765,000 12,941,000
(.17 af/yr)
Indian Agriculture
390,000af (2006)
0.5m
1.0m
1.5m
2.0m
2.5m
3.0m
Non-Indian Agriculture
1,638,000af (2006)
Non-GPCD
175,000af (2006)
GPCD Uses
1,120,000af (2008)
(200 GPCD average x 5,000,000 population)
Commercial
Farming
2,028,000af
“Urban” Uses
1,295,000af
V
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Running out of water is not imminent. Nor is it conceivable that resi-dents
of the Sun Corridor will turn on their taps and have nothing
come out. The existing vast plumbing systems, storage mechanisms
and redundant supplies are all designed to protect urban domestic
use as the paramount water demand. But how we use water in the Sun
Corridor is—and will remain—the defining characteristic of this place.
The question ultimately becomes how much Sun Corridor residents
should adjust their lifestyle and uses of water to accommodate more
residents. Using less water per capita will change the way people live.
But it will also mean that the water supply can be stretched further.
This essential tension manifests itself in numerous policy choices.
• Agriculture. The simplest explanation of the Sun Corridor’s
relatively comfortable water situation is that half of its water
is used to grow crops. That huge amount can potentially be
rededicated to urban populations and can, therefore, support
long-term growth. The assumption has been that the growing
megapolitan’s future water supply will come from the gradual
transfer of water from agriculture to urban uses. But agricul-tural
water and urban water are often not the same commodity,
and shifting from the former to the latter “hardens” the demand
and erodes management flexibility. In other parts of the country,
preserving local agricultural suppliers is an important issue of
sustainability, healthy lifestyles, maintaining historic cultures,
land use and open space preservation, and anti-globalization
trends. All of those issues deserve greater discussion in the
Sun Corridor, but the issue of water-management flexibility
may well be far more important.
Suppose, for example, that 500,000 acre feet of Indian water is
permanently used for farming. This policy choice might be made
by central Arizona’s tribal communities. At an average use of
150 GPCD, that’s 2.9 million fewer people to be accommodated.
• Economic development What kind of an economy do we
want to have? How does water use support or limit our econo-my?
Electronics manufacturing, still a staple of the East Valley’s
economy, uses a lot of water, but does so efficiently and adds
high economic value. Growing alfalfa uses a lot of water and
has relatively low economic value. Golf courses are high water
uses, but if coupled with resort hotels, are a mainstay of tourism,
which “imports” dollars into the Sun Corridor. Solar power is
a current piece of the state’s economic development strategy,
but some kinds of solar power generation are high water users.
Expanded copper mining—it was, of course, a preeminent
member of the “five C’s”—uses a lot of water, often in ways
that are not fully accounted for in GPCD projections.
How water supports the economy we want to build must be
more carefully integrated into economic development planning.
• Where should we grow? All parts of the Sun Corridor are
not equal. The big cities of the Phoenix metro area, especially
those parts within the boundaries of the Salt River Project, have
the largest, most reliable and most flexible water supplies. But
most recent growth has taken place in smaller municipalities
on the west side, and in the high-growth mid-Corridor geog-raphy
of Pinal County. Over the long term, this may not be a
sustainable growth pattern. Either new (and potentially less
reliable) water supplies will be needed to support urbanizing
areas, or existing supplies will need to flow toward develop-ment,
or development will need to migrate to areas with firmer
supplies. This may well be manifest in a clash between market
forces pushing homebuilding outward and legal and institu-tional
protections of existing water rights pushing additional
development into older neighborhoods.
• urban form. If development is to move where the most reli-able
supplies are, the existing built up areas of the Corridor
must become more dense. The single-family detached home
has been the essential building block of the Arizona lifestyle.
But there is evidence that this may begin to change because of
price and consumer preferences. Higher-density developments,
ranging from patio homes with community swimming pools to
multilevel condominiums, consume less water on a per capita
basis.74 Smaller lots present less landscaping area and have
a higher percentage area covered by impervious surfaces like
roofs and driveways. At significantly higher densities, in multi-family
apartments or condominiums, landscaping per resident
is even further reduced and may be subject to professional
management. Work by Professor Patricia Gober at ASU sug-gests
a dramatic decline in per capita water use at increasing
density. But her colleague Ray Quay cautions that recent Phoenix
data suggests a need to revisit this relationship. Density may
not always be the critical variable; income can be as significant
at higher densities as it is in single-family developments.
Water use is related to residential densities
Source: DCDC. Water duties from Salt River Project (2003) Canal Available Capacity
Report, Table 2, 1995 Urban Water Duties in AF/Acre. Population densities based on
land use classifications from Maricopa Association of Governments 1995 Land Use
Classifications, http://www.mag.maricopa.gov/.
0
0.1
0.2
0.3
0.4
0.5
0 20 40 60 80
Water Duty
Log (water duty)
0.6
People per Acre
Water Use per Person, Acre Feet
Mo r r i s o n INs t i t u t e f o r p u b l i c p o l i cy | 35
• Landscaping. If Phoenix were to stop watering its existing
Midwestern plant palette, the grass and trees would die and the
area would become markedly more barren. Some of the trees
that would die are 50 years old and more. Some are located on
old golf courses, in historic neighborhoods with an agricultural
heritage, in city parks or on the ASU campus. Should some of
this landscape go? Phoenix will only reach Tucson’s per capita
consumption range through such drastic action. Doing so is
at odds with Phoenix’s history—and may exacerbate the “heat
island” effect. But reducing our water use for landscaping
remains the most effective way to stretch the water supply. Do
we give up the “oasis” nature of the older parts of the city in
order to accommodate even more residents?
• The Lifestyle of Affluence. Low-density single-family
homes, lush landscaping , golf courses and multiple cars are all
pieces of the lifestyle of affluent twentieth century Americans.
In the hot desert of central Arizona there’s another simple proxy
for that lifestyle: nearly 30% of metropolitan Phoenix residents
have private backyard pools,75 one of the highest percentages
in the world. Many of them consider their pools essential to
a bearable summer. The average backyard pool holds about
16,000 gallons of water.76 Evaporation uses nearly 10,000
gallons or more per pool each year.77
Private swimming pools are an icon of a lifestyle of abundance
that may be coming to a close for a variety of reasons related to
average income, the price of housing, the end of cheap petro-leum
and a host of deep changes in the nature of society. This
particular use of relatively cheap, apparently abundant water
also crystallizes a sense of choices and priorities about living
in the Sun Corridor. Will the day come when pool construction
is limited to those serving larger numbers of people? Or is it
more important to continue allowing individual pools? Is this
an issue to be resolved through regulation or price or evolving
social preferences? Are you willing to give up the right to a
backyard pool so that we can have a more reliable supply, or
maintain local agriculture, or support natural ecosystems, or
allow more people to move into the Sun Corridor?
• Aesthetics and Urban Environment. On July 20, 2010,
the rubber dam that held back the Tempe Town Lake cracked
and burst. Nearly a billion gallons of water moving at 15,000
cubic feet per second rushed down the Salt River channel.78
Following the break, some people called for not refilling the
lake because it was a “waste of water.” Tempe, however, cites
the lake as the second most-visited tourist attraction in Ari-zona
(after the Grand Canyon). The city also views the lake
as an engine of economic development because apartments,
condominiums and other development have occurred along
its shores. Perhaps most importantly, the lake has become a
gathering place in an urban area that too often seems merely
a seamless web of beige houses and big-box retail centers. If
the Sun Corridor is to offer the kind of urban excitement and
amenities other cities have, it will require punctuation marks
throughout the urban fabric that concentrate populations and
convene people for social and artistic reasons. Harbors, rivers
and lakes have always been places where people congregate.
Is this an appropriate use of Sun Corridor water? Similar uses
exist in Scottsdale’s Indian Bend Wash and Phoenix’s riparian
habitat, among others. All are examples of how water can be
used to focus the celebration of human life. True, a less water-consumptive
alternative to Tempe Town Lake might have been
possible, but using water to celebrate life in an arid environ-ment
is a basic notion of shared civilization. We can and should
integrate water into our urban environment in a way that is both
efficient and also provides amenities and supports natural sys-tems.
Canals run throughout many urban areas and can serve
as paths and trails. Historically, many canals were lined with
trees that we cut down to save water—only to use that water
to plant new trees in our backyards. Cutting off all celebration
of water for its life-giving quality in the desert simply to support
more residents is not a rational choice.
�� The Natural Environment. The most fundamental trade-off
of all is the question of to what extent the natural environ-ment
of ephemeral desert washes, free-flowing streams and
riparian habitats deserves to be protected. In the era of manifest
Lush, exotic landscaping Native plants, xeriscaping
Generally, higher-density developments use less water per capita. But landscape choices still highly influence per capita water use.
36 | Wat e r i n g t h e S u n C o r r i d o r
destiny and the settling of the West that question was clearly
answered: uses for people, in farming and building settlements
trumped all natural things. Dams, canals, pumping, irrigation
and long-distance conveyance of water are all pieces of that
decision. In the Sun Corridor there isn’t much natural use of
water left. But the pressures to continue building a huge urban
area in the desert will increasingly require dewatering an ever
larger area. It is often said that the era of dam and great canal
building is over, partly because many of the best sites are already
used, partly because of today’s environmental demands, and
partly because America’s appetite for building great public
works seems diminished. But to what extent will we try to protect,
or even restore natural environmental benefits in the use of
water in the future?
These questions represent the crux of a debate about water use in
the Sun Corridor that must unfold over the next decade or more. The
future involves complex societal choices which will necessarily be
made through a combination of market forces, government regula-tion
and behavioral attitudes. The better informed we are about water
issues, the more likely that careful decisions will emerge.
Every bit as important as the potential “answers” to these questions
is the process by which they are considered and debated. Arizona,
and the Sun Corridor in particular, has long dealt with its water
issues through complex, fragmented, overlapping institutions. Cities,
counties, water agencies, public and private providers, special districts,
the Arizona Department of Water Resources, the United States Bu-reau
of Reclamation, tribal governments, nonprofit organizations and
a host of associations have all played a role in the water decision-making
process. This multiplicity of actors is sometimes inefficient
and slow moving. But it has served us well. Having issues debated
over and over, dissected, fragmented, and reexamined is beneficial
when thinking about very long-term consequences and planning
horizons. Making decisions in small increments is a good system for
avoiding a big mistake. As challenges mount and increase in velocity,
however, it may be time for some institutional change. A host of
questions about decision making structure needs to be part of the
debate. Should more “Sun Corridor wide” thinking be represented
by new entities? Will the Department of Water Resources ever be
rebuilt to its former capacity? Should municipalities more deliber-ately
coordinate their regulatory and pricing policies for consistent
goals and administration? What about the consistency of messages
to the public?
Decisions about water are inherently political, but often require
larger-scale and longer-term thinking than is typical of political bodies.
Institutional evolution has occurred in Arizona’s past: SRP, CAP and
ADWR were all political creations within this challenging context.
Dealing with the challenges of the Sun Corridor’s future will spur
further evolution.
As choices are made and decisions i