Tip Sheets

The ‘missing puzzle piece’ to the American West’s water future: precipitation

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Jeff Tyson

An ongoing water crisis in the West has seven states struggling to agree on how to divide water from the Colorado River, leaving the federal government to forge a plan that will likely lead to litigation. Meanwhile, scientists are forecasting all-time low levels in the nation’s largest water reservoirs, Lake Mead and Lake Powell, and a recent report warns that Utah’s Great Salt Lake is “on track to disappear in five years.” 

Flavio Lehner

Climate scientist and assistant professor of earth and atmospheric science

Warming temperatures help set the stage for continued water decline, but much of the West’s water future hinges on the future of precipitation — a factor researchers are still trying to better understand, according to climate scientist Flavio Lehner, who has monitored water supply in the Southwest for about a decade.

Lehner says:

“Warmer temperatures decrease the portion of precipitation that ends up in the Colorado River and in the reservoirs. So even if precipitation remains constant, we expect a decline in available water. That’s why there is little hope for things to return to ‘normal’ this century - we’re seemingly locked into a drier future. Unfortunately, over the past 40 years, we’ve also seen a decline in precipitation over this region, making things bad much quicker. 

“Therefore, despite the clear influence of warming, the real elephant in the room is precipitation. Warming alone typically does not cause a drought. It can make a drought worse, yes, but it typically starts with a precipitation deficit. While warming is guaranteed to continue with further greenhouse gas emissions, we don’t know yet what’s going to happen to precipitation.

“If precipitation continues to decline in the Southwestern U.S., things will get worse quickly. If it rebounds, we might get a short breather to figure out a sustainable way to manage the Colorado River. Research into what will happen to precipitation is thus critical - it’s the missing puzzle piece to the water future of the Southwest.” 

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