#ColoradoRiver mainstem streamflow on downward trend against average in this century #COriver

View of Lake Mead and Hoover dam. Photo credit BBC.

From The Desert Sun (Ian James):

After a 17-year run of mostly dry years, the Colorado River’s flow has decreased significantly below the 20th century average.

Lake Mead, the largest reservoir in the country, now stands just 39 percent full. The level of the reservoir behind Hoover Dam has been hovering a bit above historic lows during the past year, helped by a bigger snowpack last winter and strides in water conservation.

But with scenarios of the reservoir falling to critical lows looking very possible in the coming years, managers of water agencies in California, Arizona and Nevada have signaled their interest in finalizing a deal under which they would take less water from Lake Mead in an attempt to head off severe shortages.

It’s not clear how much longer it might take for officials at water districts in the three states to agree on the details of the proposed Drought Contingency Plan, which they’ve been discussing since 2015. But given the enormous strains on the river, the disconnect between its flow and the amounts diverted, and the growing impacts of climate change, experts say this sort of agreement seems a necessary first step toward preparing for a hotter and drier future in the Southwest.

“It’s great to have the structural deficit taken care of, and that’s frankly what the Drought Contingency Plan does is take care of that,” said Brad Udall, a water and climate scientist at Colorado State University. But if the flow of the river decreases more in the coming years — by say, more than 20 percent, for example — he said those measures won’t go far enough in “dealing with the conflict that will fall out of such declines.”

In March, Udall and fellow climate scientist Jonathan Overpeck published research in which they found that reductions in the river’s flow averaged 19 percent per year between 2000 and 2014. They estimated that somewhere between one-sixth and one-half of that loss in flow was due to higher temperatures — 0.9 degree Celsius, or 1.6 degrees Fahrenheit, above the average over the previous 94 years.

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