Report: Climate change could cut river flows

Climate change may result in about a 9 percent drop in average Colorado River flows over the next half-century, the U.S. Bureau of Reclamation says in a new report.

Drought frequency and duration are expected to increase under a climate-change model, one of several water-supply scenarios being considered by the agency in an ongoing study of supply and demand in the Colorado River Basin.

“Droughts lasting five or more years are projected to occur 40 percent of the time over the next 50 years” under the climate-change assumption, it says.

The projected drop in flows is for average natural flows at Lees Ferry in Glen Canyon. Natural flows are flows that would occur if not for upstream water diversions and reservoir storage.

The report projects continued warming in the basin, with the biggest changes in spring and summer and in Upper Basin rather than Lower Basin states. One result will be more rain and decreased snowpack.

The river’s watershed irrigates almost 4 million acres in the basin, which produces about 15 percent of U.S. crops and 13 percent of its livestock, the report says. It also meets the municipal water supply needs for more than 30 million people in basin states. But there’s already an imbalance between supply and demand in the basin, it notes.

“This imbalance will grow in the future if the potential effects of climate change are realized and demands continue to increase,” it says.

The interim report is the first in a series that the bureau plans to release as the study continues. The study is being funded by the bureau and basin states.

The study will explore solutions that could include water conservation and reuse, changes in reservoir operations, desalinization, groundwater development, conversion of agricultural water to urban uses, water-supply augmentation, and cloud seeding, according to the report and a news release from the Colorado Water Conservation Board.

The Environmental Defense Fund, a conservation group, praised the report but said future reports should look at how to sustain healthy river flows and related recreation and tourism industries.


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