The #ColoradoRiver and #ClimateChange #COriver

From KUNC (Jackie Fortier):

“Every major city gets water out of this basin. 40 million people, seven states, two nations, 22 federally recognized Indian tribes — everybody depends on it,” said Brad Udall, senior water and climate research scientist at Colorado State University.

According to a new study by Udall and Jonathan Overpeck, a climatologist at the University of Arizona, this essential river is seeing its water levels drop due to climate change.

The researchers contrasted the most recent drought on the river — from 2000 to 2014 — with another one from the mid-1950s to about 1967. The earlier drought’s primary cause was a sharp fall in precipitation. In the most recent drought, however, the primary factor was heat.

“Since 2000, the Colorado River has been in a drought. The flows are down about 20 percent. We say that about a third of that reduction is due to the higher temperatures that we are now experiencing in the 21st century,” Udall said.

Since 2000, temperatures have risen on average 1.6 degrees Fahrenheit above normal in the Upper Colorado River Basin annually. Udall and Overpeck found that the hotter weather stripped the river of at least 500,000 acre-feet of water. That’s enough water for half a million families of four for a year according to the U.S. Bureau of Reclamation.

Where is the water going? Into the atmosphere, ecosystem and human consumption and agriculture.

“We now have snowmelt two to three weeks earlier, so you have a longer period of time for plants to use water, you have hotter conditions so the plants use more water and the atmosphere as the climate warms demands more water. It’s a bigger suck, if you will, for moisture,” Udall said.

The researchers predict that as weather continues to warm over the next three decades, the water in the Colorado River will decline by about a quarter. That would be a dramatic impact on a river that supplies water to 40 million people in seven western states, including Colorado. By the end of this century, the river could drop by more than half, far more than federal water managers have predicted.

But some scientists aren’t so sure.

“So this is my question: is this drought, are we going to recover, is it climate change and we’re not going to recover, how much of each — the paper doesn’t quite address that. It certainly doesn’t do the science to get at the bottom of it,” said Martin Hoerling, a research meteorologist specializing in climate dynamics at NOAA’s Earth System Research Laboratory in Boulder, Colorado. He was not involved in the study.

“That’s a big deal. Now, I’m saying this like it’s a certainty — it’s not. But the aggregate, the average, of all the models do indicate a wetter climate,” Hoerling said. “Why? Well it may simply be the water vapor content is going to be more abundant, so when storms come they will be able to bear more moisture and when they drop that moisture there will be more snowpack as a result in the core of winter in the upper Colorado River Basin. That effect is enough to compensate for most of the warming.”

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