Even the way snow is falling and melting is changing — Bloomberg

Westwide SNOTEL basin-filled map Janiuary 18, 2018 via the NRCS.

From Bloomberg (Daniel Rothberg):

“Water and climate change are joined at the hip,” said Brad Udall, a researcher at Colorado State University who published a paper earlier this year showing how climate change has reduced flows in the Colorado River. “One of the primary impacts of a warming atmosphere are changes to our water cycle.”

Snowpack is 50 percent lower than the average at this point in the winter at dozens of basins in the region. It’s a major concern in a region with a growing population where water supplies are often pushed to their limits, even in good years. In addition to fueling the West’s winter tourism industry, the snow provides a steady supply of water for the Colorado River, which serves 40 million people spread from Denver to Los Angeles.

The problem is not just a lack of snow, but changes in how it is falling and melting. Think of the snowpack as a natural reservoir. During the winter, it freezes in place. When temperatures rise in the spring, the water within is released gradually, filling reservoirs through the rest of the year. That pattern is fracturing around the world. A study released Wednesday by the University of Potsdam also found less available water from snowpack in High Mountain Asia from 1987 to 2009.

In the western U.S., the snow line is receding to higher elevations—typically above 8,000 feet. Below that line, rain is often falling instead of snow, meaning less precipitation is stored in the snowpack. A big storm might send water to reservoirs, but many pools weren’t built to hold a deluge of rain. As a result, they often have to release the water to avoid flooding.

Without predictable snowpack melts, “it reduces reliability on the supply side,” said Demetri Polyzos, a senior engineer for the Metropolitan Water District, the wholesale water agency for Southern California.

There have been bad starts to the snow season before, and climatologists say it’s too early to rule out the possibility that the Western snowpack will bounce back. But even if it does return to average—or above average—levels, researchers said it is unlikely that critical waterways like the Colorado River would get their normal runoff.

“As it warms, you get less runoff,” said Jonathan Overpeck, a climate scientist at the University of Michigan who co-authored the Colorado River drought paper with Udall.

The short-term effects may be manageable. Because 2017 was a wet year, most reservoirs have enough stored water to satiate municipal and agricultural demand through even a dry, hot summer. But water managers still need to respond to the long-term threat.

Western snowpack could decrease by an average of 60 percent over the next 30 years due to anthropogenic warming and natural climate trends, according to an article published last year in Nature.

Detailed Colorado River Basin map via the U.S. Bureau of Reclamation.

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