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UA researchers predict future drought for the southwest

Arizona Summer Wildcat

New pressure pattern may put more severe strain on water

The southwest may be entering a severe 10-year drought do to a change in pressure patterns, according to research from UA climate scientists.

"We all should begin thinking seriously about the impacts of extended dry conditions, and what viable alternatives exist for coping, what contingency plans we need," said Barbara Morehouse, director of the University of Arizona's Climate Assessment Project for the Southwest.

This region may be shifting into a new phase of the Pacific Decadal Oscillation. The long-term Pacific sea temperature and sea surface pressure pattern has a large impact on the climate of the western United States.

The Pacific Decadal Oscillation is a relatively regular pattern of high and low pressure systems off the coast of western Canada. This pattern operates on a 20- to 30-year time cycle.

A severe drought occurred in this region in the 1950s and scientists are worried how a similar drought might affect the water supplies of Phoenix and Tucson in the year 2025.

Past shifts in this pattern occurred in 1925, 1947 and 1977. Climatological data has suggested to some that another shift occurred in 1995.

Researchers know that this pattern is tied to the moisture patterns of western North America, Morehouse said.

Since 1977, the southwest has had relatively wet winters and this winter precipitation is the major means by which this region receives moisture. If this pressure system did shift to its alternate phase in 1995, the Southwest may be short on renewable water for the next several decades, Morehouse said.

UA scientists have modeled the effects of such a drought on water supplies in Phoenix and Tucson based on the 10-year drought conditions that occurred in the 1950s and the Arizona Department of Water Resources estimates of Phoenix and Tucson water needs in 2025.

Even assuming full availability of Central Arizona Project water, the water demand could exceed the renewable water supply by 39 percent, according to the CLIMAS study.

That's a 15 percent increase above the 24 percent overdraft already projected for Phoenix for 2025, Morehouse added.

Assuming the wet conditions that have been present over the past few decades, a period that has seen tremendous growth in the Phoenix and Tucson area, will continue into the future contradicts information about the climatological history of the southwest, according to researchers.

This project is funded by the National Oceanic and Atmospheric Administration.