Feb 20, 2020

Climate change has stolen more than a billion tons of water from the West’s most vital river

Colorado
Arizona
California
New Mexico
Utah
Nevada
Wyoming
USA
by
Juliet Eilperin
,
Washington Post
Climate change is decreasing snowpack, which is increasing evaporation in the Colorado River.
The Colorado River near Peach Springs, Arizona. Credit: Justin Sullivan/Getty Images

Climate Signals Summary: Increasing temperatures due to climate change cause snowpack to melt earlier and more precipitation to fall as rain rather than snow, both of which leads to overall snowpack decline. Reduced snowpack is affecting water resources in the western United States. 


Article Excerpt: The Colorado River’s average annual flow has declined by nearly 20 percent compared to the last century, and now a new study has identified one of the main culprits: Climate change is causing mountain snowpack to disappear, leading to increased evaporation.

Four recent studies have found that up to half of the drop in the Colorado’s average annual flow since 2000 has been driven by warmer temperatures. Now, two U.S. Geological Survey researchers have concluded that much of this climate-induced decline — amounting to 1.5 billion tons of missing water, equal to the annual water consumption of 10 million Americans — comes from the fact that the region’s snowpack is shrinking and melting earlier. Having less snow to reflect heat from the sun, known as the albedo effect, creates a negative feedback loop, they say.

...

The new findings are significant because about 40 million Americans living across the West depend on water from the Colorado River, which supports $1 trillion in economic activity each year. The water is shipped as far away as California’s Imperial Valley and central Arizona, where farmers use it to irrigate crops, as well as across the Rockies to supply drinking water for Colorado’s biggest cities.

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The region is poised to warm even more in the years ahead, Milly said, and it isn’t “likely” that precipitation can compensate for these hotter and drier conditions. Comparing the Colorado River’s historic flow between 1913 and 2017 to future conditions, he added: “That flow, we estimate, due to the warming alone would be reduced anywhere from 14 to 31 percent by 2050.”

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Under a 1922 compact, Upper Basin states — Colorado, Utah, Wyoming and New Mexico — must deliver an average of 8.25 million acre-feet of water in 10 consecutive years to the Lower Basin states — California, Arizona and Nevada — and Mexico. (An acre-foot is what it takes to cover an acre of land in a foot of water, or roughly 325,000 gallons.)

But now that the Colorado River’s average annual flow is nearly 20 percent below its historic average, this has put pressure on the system. Its two biggest reservoirs, Lake Powell and Lake Mead, are just under half full.

The current operating rules for the river expire at the end of 2026, and negotiations over how to share the water going forward start this year.

Udall said that in light of current projections, policymakers need to consider crafting an agreement where all the major players in the West will use less water than they do now.