The orange color reflects on the Colorado River, seen from the Ocean to Ocean Highway Bridge and Southern Pacific Railroad Bridge in East Imperial, Calif., as the sun rises over Yuma, Arizona, Tuesday, Jan. 10, 2017. The guard tower at Yuma Territorial Prison State Historic Park can be seen through the Union Pacific Railroad bridge at right.

(Randy Hoeft/The Yuma Sun via AP)

At a Glance

The Colorado River is shrinking, and climate change is at least partially to blame, scientists say.They say it's only going to get worse in the latter half of the century if greenhouse gas emissions are not reduced.

The Colorado River, one of the most important waterways in the United States, is shrinking as a result of climate change and the worst is yet to come, two scientists say.

According to a , the scientists determined that the river's volume has dropped more than 19 percent during the drought that has gripped the region since 2000, and the shortage of precipitation can only account for about two-thirds of that decline.

Hydrologists Brad Udall of Colorado State University and Jonathan Overpeck of the University of Arizona say the rest of the decline is due to a warming atmosphere induced by climate change. The researchers used existing climate models to determine that the decline in precipitation should have only produced a reduction of about 11.4 percent in the river flow, not the 19.3 percent that actually occurred.

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They say the discrepancy can be attributed to higher temperatures, which "increased evaporation from water and soil, sucked more moisture from snow and sent more water from plant leaves into the atmosphere."

The scientists note that "future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur."

The scientists also said impacts of further shrinking of the important waterway could create enormous problems for cities and farmers.

"The Colorado River Basin encompasses seven states and northern Mexico and is home to 22 federally recognized tribes," said the scientists. "The river provides municipal and industrial water for 40 million people distributed across every major Southwestern city both within and without the basin, including Los Angeles, San Diego, Las Vegas, Phoenix, Tucson, Salt Lake City, Denver and the entire Front Range of Colorado, Albuquerque and Santa Fe."

For their study, Udall and Overpeck analyzed temperatures, precipitation and water volume in the basin from 2000 to 2014, comparing the data with historical data, including a drought that lasted from 1953 to 1967, the Associated Press noted. Temperature and precipitation records date to 1896, and river flow records to 1906.

Temperatures in the 2000 to 2014 period were a record 1.6 degrees Fahrenheit above the historical average, while precipitation was about 4.6 percent below average, they said.

Udall and Overpeck foresee a wide range of economic and social implications if the river continues to shrink.

"With reduced water supplies, much will have to change in these agreements to address equity, economics and social concerns on regional, state, basin-wide and even national levels," the researchers conclude. "Climate change threats to western water supplies are very realand should prompt great concern and urgency among both water managers and the citizens of the Southwest."

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Aerial image of the winding Colorado River meeting the Pacific Ocean in Baja, Mexico. (Jassen Todorov/Caters News Agency)