Drought in Perspective

Most of the western United States has experienced moderate to severe drought conditions for the last ten years and evidence shows drought conditions could continue for as long as 20 to 30 years; this includes Arizona.

Long-range planning, investments in water supply alternatives, and a history of successes in water conservation have allowed the city of Phoenix to weather this drought without resorting to mandatory water use restrictions or prohibitions. However, the city is prepared to establish such restrictions in future years if necessary.

Though Phoenix has an adequate supply of water, residents and business owners are encouraged to review their water use, and to plan for changes in how they use water to avoid more serious impacts should drought become more severe. [Why so Dry? Science @ NASA]


Caption plum:Lake Mead, August 2003

Phoenix Water Services and Drought

In Arizona this current drought has now surpassed the worst drought in the last 110 years of recordkeeping. Beyond the written record, tree ring research reveals that 20 to 30 year droughts were not uncommon over the past 1,000 years in the major watersheds serving the city of Phoenix and surrounding municipalities.

During this current drought, Phoenix has been able to manage its available water supplies to meet the community's water demands. However, this record-setting drought is a warning. Given that we could experience another 10 or more years of drought, we all need to become more aware about the facts of drought and what the future possibilities and impacts from drought could be.

Though the city of Phoenix has adequate water supplies to meet the community's water needs for the next several years even if drought continues, it is important to be aware of the steps that can be taken now to avert potential future impacts from severe, sustained drought. This report provides an overview of the facts about the current and possible future conditions of drought and what actions can be taken to reduce the impact of continuing drought.

Phoenix’s Water Supply Portfolio

The city of Phoenix maintains access to several types of water supply including: surface water, groundwater, and effluent or “reclaimed” water. For normal years (in which our supplies are unaffected by drought), about 95 percent of customer drinking water demand is met with surface water from two major sources. Salt River and Verde River surface water is delivered through the Salt River Project (SRP) and Colorado River water is delivered via the Central Arizona Project (CAP) canal. The remaining five percent is groundwater pumped from city-owned wells. In addition, in recent years, reclaimed water has become the major irrigation supply for several parks and golf courses.

Drought and Our Source Watersheds

The watersheds that supply surface water to Phoenix are much larger than the city or the metropolitan area as a whole. The Salt and Verde river watersheds encompasses 13,000 square miles in the eastern and north central portions of Arizona, and the CAP watershed encompasses much of seven states.

NOAA National Drought Monitor Map 
(click on the above map to see the most current conditions)

These watersheds receive precipitation mainly in the form of snow in the mountains. When there is insufficient snow, runoff flows are low, soil moisture decreases, and drought conditions exist both on the watershed and in the desert valleys.

Reservoir storage on the river systems helps balance out naturally occurring fluctuations in snowfall and runoff from year to year, to better match availability of water with water demand. Long, continuous periods of reduced snowfall and scarce rains, however, have a cumulative effect on the reservoir storage and reduce the ability of the storage system to even out the good and bad precipitation years.

Most of the Southwestern United States continues to experience persistent moderate to severe drought conditions. The Verde River and the Salt River combined have had only two adequate runoff seasons in the past eleven years. This drought constitutes the longest in the past 110 years of recordkeeping.

As of early March 2006, SRP reservoirs are at 76 percent of capacity, up from 42 percent two years ago. However, runoff is expected to be well below normal for the year. SRP may choose to purchase excess CAP water in 2006 to help preserve SRP reservoir storage. Seven tears of drought on the much larger Colorado River system have left that storage system at 57 percent of capacity. While well below normal, this is an improvement from 2004 when the combined reservoir storage was at a historic low point of 50 percent of capacity. The much larger size of these reservoirs has allowed downstream users, including Arizona, to continue to draw water at normal levels. In 2003 and 2004, Phoenix and other area water providers were able to take higher than normal quantities of CAP to help SRP in preserving reservoir capacity and to make up for lower in-state runoff. Phoenix may do the same in 2006 since ample CAP water exists.

Although each successive year of continued drought lowers the probability that the drought will continue, that does not mean that the end of the drought is in sight. Tree ring research, such as conducted by the University of Arizona, indicates that during the past millennium, droughts of 20-year to 30-year duration were not uncommon for the west.


How is Phoenix Faring?

Fortunately, due to visionary water supply planning efforts over the last 100 years, Phoenix and surrounding municipalities have successfully managed available water supplies to meet growing demands with little if any impact on the economy and quality of life for the region. Abundant (though currently diminishing) storage in major reservoirs on the Colorado River and on the Salt and Verde Rivers and the ability to pump groundwater has allowed our region to continue to thrive despite the recent drought conditions.

About two-thirds of Phoenix’s water serves residential uses, including landscape irrigation. The remaining one-third is used for commercial, industrial and institutional purposes. More than 60 percent of Phoenix’s overall water demand is for outdoor water uses (primarily landscape irrigation).

Demand, based on the overall GPCD (gallons per capita per day), has been reduced by about 21 percent in the last 25 years. This can be attributed to a number of factors, including new homes built with low water use plumbing fixtures and appliances, new landscape restrictions requiring the use of desert adapted plants, increased use of reclaimed water on new golf courses and parks, and water conservation education programs.

Though drought has affected both systems, the Salt/Verde watershed is much more sensitive to drought given the smaller watershed size. This smaller size means that local weather conditions have a greater impact on water yield. On larger regional watersheds, localized weather phenomenon has less impact on the watershed as a whole.

Low storage conditions in the Salt and Verde River reservoirs prompted SRP to reduce allocations to users by one-third in 2003 and 2004 for the first time in 50 years. However, the heavy runoff season of 2004-2005 led to a return to normal SRP allocation levels. During the term of the reduction, high priority water rights available to the city helped minimize the impact of these reductions on Phoenix. To date, similar allocation cutbacks have not been necessary on the Colorado River/CAP system due to the more substantive storage. Because Phoenix has access to additional CAP supplies beyond current demands for that water, the city has been able to use this water to compensate for impacts caused by the SRP reduction in areas outside the SRP service area. As a result, Phoenix customers have not been impacted by this reduction. These compensating supplies are expected to remain available for at least the next five to 10 years, even with continuing drought conditions. In addition, groundwater pumping from city wells can be accelerated to help offset reductions in surface water supplies.

Future Uncertainties

Although Phoenix currently benefits from a diversified water supply portfolio, we are not immune from drought. It is possible that reductions in allocations of Colorado River Water to the State of Arizona or future more severe reductions in SRP allocations could result in the city of Phoenix incurring a supply shortage in meeting the community's normal water demands. While determining the precise timing and nature of these impacts is not possible, identification of the factors and uncertainties that bear on drought conditions is an important first step in preparing for these potential water supply shortfalls. Key uncertainties are:

  • Growth rate within our service area;
  • How the seven Colorado River Basin states, and groups of water users within Arizona, will respond to system shortages;
  • The degree to which customer demands can be reduced through permanent conservation or through temporary point-in-time demand reductions to meet drought conditions;
  • How long this drought will last.

The Growth Factor

Most new development utilizes low water use systems and landscaping. Thus, the average household water use of a new house is less than the average household water use of existing houses more than 10 years old. Commercial and industrial uses are also more efficient than past uses. The result is that in the city of Phoenix, the rate at which total water consumption is increasing is lower than our growth rate. To illustrate, the city's population has grown by 77 percent since 1980, though the water use has grown by only 35 percent.

For the last 16 years, Phoenix has required new development to pay a water resources acquisition fee to help fund new water supply acquisition and development. This means growth forces are offsetting the cost of the acquisition and development of new water supplies. In a drought situation, such water supply development may prove critical. Thus, growth "pays its own way" in ensuring that it does not increase the city's vulnerability to drought.

Over the last five years there has been a great deal of community discussion about growth. The general consensus is that while the community does not like some of the negative effects of growth (such as congestion and declining air quality), it welcomes the economic benefits. We want those benefits to continue, but we want to manage growth to limit its negative effects. Phoenix’s General Plan, as well as the General Plans for most cities in the region, is structured around this basic strategy.

That Phoenix has a healthy economy is fueled in large measure by regional growth. The city of Phoenix population has been steadily increasing at a rate of approximately three percent per year. The regional growth rate is 3.9 percent per year outside Phoenix’s city limits. The city’s strategy is growth management, not zero growth. Stopping growth would negatively impact the well being of the city’s and the region. It would cause dislocations in employment throughout the region, and significantly dampen commercial activity, manufacturing, and service industries.

Through long-range water resource planning efforts, the city continually strives to ensure that the demands of this growth can be met far into the future. These efforts involve both management of our existing supplies and acquisition of new supplies. As the drought depends, this becomes especially critical in protecting our local economy.

Shortage Sharing on the Colorado River

Under the current "law of the river," the Colorado's flow is divided by compact between upper basin and lower basin states. The lower basin states – California, Nevada and Arizona – enjoy an entitlement of 7.5 million acre feet of water per year from the river, plus enough additional water to assure the minimum flow-through of 1.5 million acre feet to comply with U. S. treaty obligations to Mexico. Arizona is entitled to 2.8 million acre-feet of Colorado River water. However, about 1.7 million acre-feet of this allocation has junior standing on the system. What that means is that a shortage in the lower basin allocation dictates that Arizona is cut back first. California and Nevada (4.4 million acre feet and 300,000 acre feet respectively) will be affected only after Arizona loses its entire 1.7 acre-feet of "junior" status water (more than half of the state's total allocation).

The CAP diverts 1.5 million acre-feet of the state's Colorado River allocation. If Arizona's allocation is cut back, the CAP supplies and other junior-status water uses along the Colorado River will be curtailed first. Within the CAP, the non-Indian agricultural sector will be cut back first. Current estimates conclude that water available to cities would not be curtailed until the CAP was cut back by at least one-third (or 500,000 acre-feet). Water planners and managers are continuing to study the timing and impacts of these potential curtailments. Barring some unforeseen legal or political action which affects allocations of the Colorado River, the Central Arizona Project estimates that there will be adequate Colorado River storage and flows to meet the city of Phoenix's normal CAP water orders through at least 2015. However the city of Phoenix, in an effort help manage our water supplies through 2011 and beyond, may require its customers to begin water reductions earlier than the occurrence of actual CAP shortages.

City Water Distribution Infrastructure

The city of Phoenix water supply system has been designed specifically to provide water during shortage conditions. The water system design allows flexibility in how to respond as drought conditions change. The growth of our city and recent drought conditions have prompted a re-evaluation of the capabilities of this system under extreme shortages. The city's Water Resources Plan Update presents an evaluation of several potential future drought scenarios as well as numerous strategies for responding to drought. The city also is updating its Water System Master Plan. These plans call for additional water system features and water supplies to increase reliability during water supply shortfalls.

Long Term Objective

The basic strategy of the Phoenix Water Services Department is to ensure that adequate supplies are available to meet Phoenix’s existing and new water demands, and to minimize the effects of drought on our economy and quality of life. Under normal conditions (including short-term dry periods), Phoenix has adequate sustainable water supplies to meet the State of Arizona's 100-Year Assured Water Supply standard. This includes growth in Phoenix's system water demand over the next 20 years or more.

It is possible, however, that during very long term drought conditions, Phoenix would have to institute mandatory water use reductions. If, as some climatologists have predicted, the current drought is actually a return to “normal” conditions from a very long wet period, many temporary drought measures may have to become permanent. It could be that we will never return to what we have come to expect as “normal” weather conditions.

The challenge for urban water planners is to creatively manage existing supplies – and acquire supplemental supplies as needed – to maintain the region’s growth-dominated economy in a sustainable manner.

Phoenix Actions to Date

Phoenix has taken measures to cut water use by requiring city departments to decrease water consumption by five percent, and by turning off city landscaping water features, such as fountains. Additional steps have included:

  • Reductions in irrigation in parks, city golf courses and streetscapes;
  • Changes in water use for dust control;
  • Changes in the cleaning of streets and sidewalks around city buildings;
  • Audits and changes to how the city uses water for cooling;
  • Elimination of over-seeding city-controlled turf facilities with winter ryegrass.

City actions, combined with increased rainfall in 2003 resulted in a drop of more than 11 percent in the city’s own water use. Phoenix has requested five percent reductions from all residents and has increased conservation education and awareness to assist the public in cutting its water use.

The provision of an adequate water supply through prolonged drought requires advanced planning for the distribution and storage of water for later use and effective management of this valuable resource.

Drought Response Strategy

Recognizing that long-term drought is possible, and that water flows can worsen during a drought, the city of Phoenix has been developing a long-term drought response strategy to better position the city to respond to changing conditions. It is only prudent for the city to plan responses for all drought stages should they become necessary in future years.

The city of Phoenix will accomplish this by doing the following:

  • Manage our water supply portfolio to meet the community’s water needs today;
  • Increase efforts to plan for water needs under conditions of continuing drought;
  • Educate our customers about the situation now and possible future conditions, and;
  • Help our customers plan and implement conservation measures they can undertake now to soften the impacts of a more lengthy and severe drought.

While conservation is something all desert dwellers should engage in at all times, it is particularly important to managing water supplies during drought conditions. Preparing and planning for drought today will ensure the proper level of drought response in the coming years.

By being careful about how you use water you can help slow down the effect drought has on our water supply. There are a number of websites with information on water conservation.

Visit the City of Phoenix Water Services Department home page for information about a variety of water issues and water conservation.

The Water - Use It Wisely website lists more than one-hundred water saving tips for our area.