Resivoirs

Published October 24, 2012

Arizona

Storage in most reservoirs across the Southwest declined in the last 12 months as a result of lower-than-average precipitation and above-average temperatures. In Arizona, total reservoir storage in San Carlos Reservoir on the Gila River and in the Salt and Verde river reservoir systems decreased by about 305,700 acre-feet during the 2012 water year (Table 2). The La Niña event, which began in September 2011 and persisted through April 2012, robbed Arizona watersheds of much-needed winter snow. That event also affected the Colorado River, where combined storage in Lakes Powell and Mead decreased by 3.65 million acre-feet (maf; Figure 3). The 2012 water year inflow to Lake Powell was 4.91 maf, or about 46 percent of average, placing 2012 as the third driest water year on record—only 2002 and 1977 registered lower inflows.

New Mexico

In New Mexico, total reservoir storage was about 431,700 acre-feet less than it was one year ago, not including changes in storage for El Vado and Heron reservoirs, which did not report storage values in October 2011. Like in Arizona, back-to-back La Niña events in the 2011 and 2012 winters helped steer storms north of the state, starving headwaters of snow and contributing to substantially lower reservoir levels than those recorded in 2010 prior to the onset of La Niña conditions. In New Mexico’s largest reservoir, Elephant Butte, storage decreased by 95,000 acre-feet, halving the amount of water that was stored in the reservoir at the beginning of the water year. As a result of low reservoir levels, irrigators in the lower Rio Grande Valley received only 10 inches of surface water—a full allotment is 36 inches. It was the ninth time in the last 10 years irrigation allotments were low. In the Navajo Reservoir in the San Juan River Basin, the state’s second-largest reservoir, storage declined by more than 293,000 acre-feet, or about 17 percent (Table 3). Reservoir storage on the Pecos River also fell by more than one-third during the water year, dropping by 6,800 acre-feet.