The Central Arizona Project is helping to relieve water shortages caused by this season's drought. And because of increased CAP deliveries Arizona will likely come close this year to using its full allocation of Colorado River water.

Despite recent July rains dry conditions continue in Arizona, fulfilling earlier expectations that this would be a very dry summer. La Niña effects were evident early in the year, and the period of January through March was the driest on record. Rain in early April provided some relief but not enough to mitigate developing drought conditions. CAP has been preparing for possible increased water demands since January by pumping extra water into Lake Pleasant. In May, storage at the lake was about 741,000 acre-feet or 13 percent above the normal storage limit of 654,000 acre-feet.

Although Arizona is experiencing drought conditions a water surplus has been declared on the Colorado River, the source of CAP water. This situation reflects the shift of storm patterns in the region. A season of heavy snow in the Rockies generally means the Arizona mountains are left high and dry, and vice versa. Interpreted hydrologically, low flow on the Salt, Agua Fria, Verde and the Gila generally means abundant flow on the Colorado River. The workings of weather favor CAP's role as a provider of drought relief.

July Rains Bring Relief, but State Still Dry Areas of Arizona received varied monsoon rainfall in July: 0.94 inches in Yuma, 2.05 in Safford, 2.9 in Phoenix and 6.8 in Tucson. The rainfall helped reduce the precipitation deficit, although precipitation over the last 12 months remains below normal. Because of last month's precipitation, drought conditions in areas of the state have eased, although a dry August could reverse the promising situation.

Although the short-term situation has improved, prospects for the fall remain in doubt. In the tropical Pacific, water temperatures are below normal, with signs of dropping further. This means the ongoing La Niña will likely linger into a second year. As a result, above normal temperatures and below normal rainfall would likely begin in September and continue into the winter. Signs point, however, to La Niña not being as strong as last winter. The warmth and dryness of the coming months then might not be as great as occurred last winter at the beginning of the drought.

Because of the dry conditions the runoff that Salt River Project normally receives between January through May was minimal this year. In fact, the period was the eighth driest on record. As a result, SRP's reservoir system, the source of much of the water for the Phoenix area, is 30 percent below normal for this time of year. As part of a strategy to cope with the water shortage SRP purchased 75,000 acre-feet of CAP water. The 75,000 acre-feet is about equal to another Saguaro Lake.

The utility also requested an additional 66,500 acre-feet of in-lieu Water Bank water, to replace groundwater that would otherwise have been pumped. Despite dipping into these water sources the utility will still need to pump 300,000 acre-feet of groundwater. This represents about a third of SRP's total annual supply. During years of more normal precipitation the utility generally pumps 50,000 to 100,000 acre-feet.

CAP water also is being used to keep San Carlos Lake from drying up. The water level of the lake is sufficiently low that reservoir releases to serve the San Carlos Irrigation and Drainage District (SCIDD) and the Gila River Indian Community (GRIC) threaten the fish population in the lake. Even with the recent rains the lake is a meager 4.4 percent of capacity. CAP will deliver 31,590 acre-feet to SCIDD and GRIC, to be used instead of lake water. This marks the second time CAP water was used to preserve the lake. In 1997, CAP delivered 17,000 acre-feet to the irrigation districts. In addition, both SCIDD and GRIC are purchasing CAP water to supplement the sparse supply from the Gila River.

Increased use of CAP water means Arizona will come closer to using its full Colorado River allocation of 2.8 million acre-feet. Current records for deliveries were set in 1997 when about 2.854 million acre-feet were used. An unmeasured return flow estimated at 246,000 acre-feet reduced this amount to an actual net use of 2.6 million acre-feet. The boost in CAP water use that year was mainly attributable to the Arizona Water Bank having come on line. CAP water use was down in 1998 because of the excess El Niño precipitation.

The May water use forecast this year anticipated 2.785 acre-feet for calendar year 1999. Actual use will probably be somewhat higher, but return flow credits again are expected to reduce this figure. Drought conditions account for the increased demand this year.

The increased CAP demand also is providing an opportunity to demonstrate the system's delivery capacity. This summer, CAP has set new daily flow records, measured in cubic feet per second (cfs). In fact, peak deliveries on June 30 and July 1 were about 3,900 cfs which at maximum flow locations along the canal exceeded the 3,000 cfs design capacity of the canal. At times last month a steady 3,600 cfs flow has been maintained, with canals on the west end of the system running about 400 cfs and about 3,200 cfs of deliveries down stream from Lake Pleasant. This is fullest capacity the canal has operated, and CAP officials say it demonstrates that the canal can run safely and efficiently at that level.