Drought in Perspective

 

Planning for Drought

Aerial view of Lake Mead sandwiched between hills.

Caption plum: Reservoir level at Lake Mead during recent drought conditions

To maintain the high standard of living enjoyed by Phoenix residents, a strong plan for how to respond to drought conditions is essential.

The City is committed to:

  • Keeping customers informed and educated about our water resources;
  • Helping our customers learn more about how to use water efficiently;
  • Managing our water supply portfolio to meet current and future demand; and
  • Increasing planning efforts to ensure reliability during drought conditions.


Why plan for drought?

In the recent past, the southwestern United States experienced persistent moderate-to-severe drought conditions. 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.

How is Phoenix planning for drought?

Though the City of Phoenix continues to have adequate water supplies to meet its future demand, it is taking steps to avert potential impacts from severe, sustained drought.

 

  • Phoenix maintains a diverse water portfolio 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 5 percent is groundwater pumped from city-owned wells. In recent years, reclaimed water has become the major irrigation supply for several parks and golf courses.
  • The watersheds that supply surface water to Phoenix are much larger than the city or metropolitan area. The Salt and Verde River watershed encompasses 13,000 square miles in the eastern and north central portions of Arizona. The CAP watershed includes much of seven states.
  • These watersheds receive precipitation mainly in the form of snow in the mountains. When there is insufficient snow, spring runoff is low and soil moisture decreases, leading to drought conditions for the watersheds and in the desert valleys.
  • Reservoirs on the river systems help balance naturally occurring fluctuations in snowfall and runoff to better match availability of water with water demand. However, long, continuous periods of reduced snowfall and scarce rains 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.

How is Phoenix faring?

Phoenix city skyline showing large skyscrapers at sunset.

Caption plum: Diligent water planning keeps Phoenix prepared for future droughts

Diligent water planning keeps Phoenix prepared for future droughts

 

  • The water supply planning efforts by Phoenix and surrounding municipalities over the last 100 years have successfully managed available supplies to meet water demand and enhance quality of life for the region. Diversified Salt/Verde watershed and Colorado River supplies, coupled with groundwater and water conservation, allow Phoenix to meet demand even in severe drought.
  • About two-thirds of Phoenix's water serves residential uses, including landscape irrigation. The remaining one-third goes to commercial, industrial and institutional customers. More than 60 percent of Phoenix's overall water demand is for outdoor water use (primarily landscape irrigation).
  • Water demand (based on the overall use per capita) has decreased by 21 percent in the last 25 years. Some of this water savings comes from homes built with low-water-use plumbing fixtures and appliances, landscape restrictions requiring the use of desert-adapted plants, use of reclaimed water on golf courses and parks, and water conservation programs.

What does the future hold?

Although Phoenix currently benefits from a diversified water supply portfolio, we are not immune to drought. Reductions in allocations of Colorado River water to Arizona or future reductions in SRP allocations could result in a supply shortage for Phoenix. Understanding the factors that drive drought response is an important first.

Response to growth. Since 1980, Phoenix's population has grown by 77 percent, while its water use has grown by only 35 percent. Due to new water-saving systems and landscape strategies, less water is used on average in new Phoenix houses than in older houses. Commercial and industrial customers also have become more efficient in their use of water. The City and other public agencies, including city facilities and parks, implemented many water conservation measures that have reduced indoor and outdoor use.

Growth forces are offsetting the cost of the acquisition and development of new water supplies. 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. The growth "pays its own way" strategy ensures that growth does not increase the city's vulnerability to drought.

Sharing water. 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 - 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).

CAP diverts 1.5 million acre-feet of the state's Colorado River allocation. If Arizona's allocation is cut, 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 first. Current estimates are that water available to cities would not be curtailed until CAP is cut by at least one-third (or 500,000 acre-feet).

Water planners and managers are continuing to study the possible timing and impacts of these potential curtailments. Barring some unforeseen legal or political action that affects allocations of the Colorado River, the Central Arizona Project estimates that there will be adequate Colorado River storage and flows to meet Phoenix's normal CAP water orders through at least 2015.

Planning for the future. Through conservation and planning for flexibility in times of shortages, the Phoenix water supply system can continue to supply water during drought conditions. Regular updates to Phoenix's Water Resources Plan and maintenance of a Water System Master Plan ensure reliability during water supply shortfalls and 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. However, during extended long-term drought conditions, Phoenix may need to institute mandatory water use restrictions.

Where can I find out more?