Climate change will increase irrigation requirements and evaporation in the #ColoradoRiver Basin

Lake Mead water levels via NOAA
Lake Mead water levels via NOAA

From the Las Vegas Review-Journal (Henry Brean):

The Colorado River faces a dual threat from climate change as rising temperatures increase the demand for irrigation water and accelerate evaporation at the river’s two largest reservoirs.

So says a new report from the U.S. Bureau of Reclamation, which predicts an 8 percent increase in irrigation demand on the lower half of the Colorado River Basin and a 10 percent increase in evaporation from Lake Mead by 2080.

The upper half of the basin, above Glen Canyon Dam in Arizona, is expected to see demand for agricultural water jump by almost 23 percent, while Lake Powell loses 7 percent more water to evaporation than it did during the last half of the 20th century.

The estimates are based on a projected temperature increase of about 5 degrees across the region.

In a statement announcing the report Friday, Reclamation Commissioner Estevan Lopez said the findings will help regulators and stakeholders address the challenges that lie ahead.

“Understanding how climate change will impact crop irrigation demand and reservoir evaporation provides vital information for the development of alternatives and solutions to meet those challenges and support the nation’s economy,” Lopez said.

Agriculture accounts for roughly 80 percent of all the water diverted from the Colorado River, so even a small increase in demand can have a significant impact on the system.

The new report is the latest in a series of region-wide risk assessments looking at the impacts of climate change on water resources in the West.

A previous bureau study predicted a 9 percent decline in the Colorado’s flow by 2050 as a result of climate change…

In all, the Bureau of Reclamation’s new report looks at 12 reservoirs on seven river systems west of the Mississippi. Its outlook is also bleak for the Truckee and Carson Rivers, which supply water to farms and communities in northwestern Nevada, Reno among them.

According to the report, rising temperatures will drive up agricultural demand on the Truckee and the Carson by more than 14 percent over the next 65 years, while evaporation will increase by 14 percent at Lake Tahoe and by 7 percent at Lahontan Reservoir.

The bureau’s projections of future irrigation demand do not account for changing crop patterns or efficiency improvements at farms.

More Colorado River Basin coverage here.

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