Saturday, May 13, 2017

Warmer Temperatures Drying the Rio Grande

Snowpacks in the Upper Rio Grande provide water used by cities and farms downstream. (Credit: Flavio Lehner) Click to Enlarge.
The intensifying effects of warming temperatures on water shortages have been detected in remote northern New Mexico, where melting snowfall feeds one of the Southwest’s most important rivers.

Researchers seeking to improve forecasts for how much water from the Rio Grande will be available for 5 million people each year found that rising temperatures are causing less of each winter’s snowpack to flow down the river as water.

The discovery showed how a warming climate “exacerbates the dry conditions whenever there's not a lot of snow to begin with,” said Flavio Lehner, a climate scientist at the National Center for Atmospheric Research who led the research.

Water in the rugged region comes in booms and busts, with boom years flush with winter storms that dump snow that melts to feed rivers in warmer months.  The effects of warming are being exacerbated in the bust years, evaporating water that’s in short supply.

“For a wet year like this year, I don’t think the effect is that big,” Lehner said.  “Whenever you have a dry year to start out with, and it’s also warm — which will become more likely in the future — then you will end up with even less water in the river.”

The effects of warm temperatures on the Rio Grande flow can be seen in measurements going back to the 1940s.  To look back to the 1570s, the scientists turned to studies of tree rings to probe the connections between temperatures, snowfall and riverflow each year.

Temperatures have risen at the Upper Rio Grande to nearly 2°F since the 1980s, a rapid rise caused by natural weather variation and global warming.  The scientists found that the low efficiency with which Upper Rio Grande snowpacks have been turning into river water since then was unprecedented for at least 445 years.

The findings were published in Geographical Research Letters this week, pointing to worsening problems for water supplies in the region and elsewhere.

Read more at Warmer Temperatures Drying the Rio Grande

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