The University of Arizona

Arizona Reservoir Volumes | CLIMAS

 SW Climate Outlook

Arizona Reservoir Volumes

Data through August 31, 2013. Data Source: National Water and Climate Center

Combined storage in Lakes Mead and Powell stood at 45.7 percent of capacity on August 31 (Figure 6), a decrease of 395,000 acre-feet from the previous month and about 9 percent lower than one year ago. The water elevation of Lake Powell peaked in mid-June and will continue to decline until spring. Monsoon rainfall has given boosts to some Arizona reservoirs, including the San Carlos Reservoir. Combined storage in the Salt and Verde river basins decreased by about 31,000 acre-feet and currently stands at 54.4 percent of capacity, down by 4.2 percent from last year.

In water-related news, the worst 14-year drought period in the last 100 years has contributed to changes in the amount of water released from Lake Powell to Lake Mead, according to the U.S. Bureau of Reclamation (BOR). Based on the best available projections of reservoir elevations and in accordance with the Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, the BOR will release 7.48 million acre-feet (maf) from Lake Powell to Lake Mead between October 1, 2013 and September 30, 2014. In recent years, releases amounted to 8.23 maf per year. As a consequence, water levels in Lake Mead will continue to decline, resulting in a 50 percent chance that the water elevation will fall below 1,075 feet above sea-level in the next two years, triggering mandated conservation strategies.


The map gives a representation of current storage for reservoirs in Arizona. Reservoir locations are numbered within the blue circles on the map, corresponding to the reservoirs listed in the table. The cup next to each reservoir shows the current storage (blue fill) as a percent of total capacity. Note that while the size of each cup varies with the size of the reservoir, these are representational and not to scale. Each cup also represents last year’s storage (dotted line) and the 1971–2000 reservoir average (red line).

The table details more exactly the current capacity (listed as a percent of maximum storage). Current and maximum storage are given in thousands of acre-feet for each reservoir. One acre-foot is the volume of water sufficient to cover an acre of land to a depth of 1 foot (approximately 325,851 gallons). On average, 1 acre-foot of water is enough to meet the demands of 4 people for a year. The last column of the table list an increase or decrease in storage since last month. A line indicates no change.

These data are based on reservoir reports updated monthly by the National Water and Climate Center of the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS).