Climate change threatens Colorado river and the water supply for 40 million people

The Weather Channel | Jan Wesner Childs Climate change has dramatically decreased natural flow in the Colorado River, jeopardizing the water supply for some 40 million people and millions of acres of farmland, according to new research from the USGS. The decline is expected to continue unless changes are made to alleviate global warming and the impacts of drier, hotter temperatures. The natural flow of the river decreased by 20% between 1913 and 2017, Chris Milly, a USGS scientists and lead author on a new study on the river, told weather.com on Friday. About half of that is attributed to higher temperatures while the rest is due to lack of precipitation, both of which are widely seen by scientists to be the results of climate change. Milly’s study specifically looked at trends toward decreasing snowpack in the Colorado River basin. “As climate warms, there is less snow cover,” he said in an email. “Because snow reflects light so well, its reduction means that the basin absorbs more sunlight.” That sunlight, in turn, fuels higher evaporation from the snowpack. “More evaporation coming off the basin means less water left to feed into the river and supply the demands of 40 million people and more than 5 million acres of irrigated cropland,” Milly said.

Climate Change Threatens Colorado River And the Water Supply for 40 Million People

By Jan Wesner Childs, weather.com, Climate Change Threatens Colorado River Basin Water Supply

Tens of millions of Americans face water shortages, as climate change threatens to dry-up a major source of water for the Southwest. At a Glance

• The Colorado River’s natural flow has decreased 20%.
• It goes down by about 9% with every 1.8 degrees in temperature increase, according to new research.
• Much of the decline is related to snowpack and evaporation.

Climate change has dramatically decreased natural flow in the Colorado River, jeopardizing the water supply for some 40 million people and millions of acres of farmland, according to new research from the USGS.

The decline is expected to continue unless changes are made to alleviate global warming and the impacts of drier, hotter temperatures.

The natural flow of the river decreased by 20% between 1913 and 2017, Chris Milly, a USGS scientists and lead author on a new study on the river, told weather.com on Friday. About half of that is attributed to higher temperatures while the rest is due to lack of precipitation, both of which are widely seen by scientists to be the results of climate change.

Milly’s study specifically looked at trends toward decreasing snowpack in the Colorado River basin.

“As climate warms, there is less snow cover,” he said in an email. “Because snow reflects light so well, its reduction means that the basin absorbs more sunlight.”

That sunlight, in turn, fuels higher evaporation from the snowpack.

“More evaporation coming off the basin means less water left to feed into the river and supply the demands of 40 million people and more than 5 million acres of irrigated cropland,” Milly said.

(MORE: NASA Images Show Dramatic Melting During Antarctica Heat Wave)

The study, published Thursday in the journal Science, estimated that river flow declines by about 9% with every 1.8 degrees in temperature increase.

The Colorado River drainage basin covers some 246,000 square miles, including all of Arizona and parts of California, Colorado, New Mexico, Nevada, Utah, and Wyoming. The river stretches some 1,450 miles from Colorado and Wyoming and across the border into Mexico. It includes two major reservoirs – Lake Mead and Lake Powell – and is an important source of water for several cities including Denver, Salt Lake City, Albuquerque, Los Angeles, and San Diego, as well as agricultural lands in California and Mexico.

Much of the basin’s region is in moderate drought conditions with some areas facing severe drought, which also exacerbates the problem.

“Besides temperature, acting mainly through the snow cover, the other big factor is precipitation,” Milly said. “As warming proceeds, gradually acting to reduce the flow, the natural ups and downs of precipitation cause ups and downs of flow, which are superimposed on the gradual decline caused by warming.”

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