With the exception of Arizona and New Mexico, snowpack across a large part of the U.S. West is looking pretty average as the season winds down. While that doesn’t conjure up visions of greatness, this is a case where reality alters perception.
“The one thing that people forget is how bad a lot of the West has been,” said Brad Rippey, a meteorologist with the U.S. Department of Agriculture. “From the perspective of a lot of folks, an average year looks fantastic this year.”
A year ago, just about 60 percent of 11 western states suffered some degree of drought, according to the latest report of the U.S. Drought Monitor in Lincoln, Nebraska. That has dropped to just over 34 percent.
That doesn’t mean things aren’t precarious. When the parts of the West listed as abnormally dry are added to the total, almost 68 percent of the land is parched. In California, where drought is moving into its fifth year, just under 99 percent of the state reaches that threshold. El Nino rain has helped some of its reservoirs reach historical average levels, but most are still low.
While people in the Eastern U.S. can rely on rain falling 12 months a year, in the West it’s a different story, said Sarah Kapnick, a research physical scientist with the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey.
Most of the region’s precipitation falls during autumn and winter, and in order to get through the year a portion of that has to fall as snow, so the moisture can be released in the spring. This isn’t just true for the U.S. West: According a 2005 paper in Nature, about one-sixth of the world’s population lives in areas where this cycle contributes to their drinking water supplies.
“Snow provides a natural reservoir to store water that falls during the cold months and then melts during the spring-summer,” Kapnick said.
All the rain can’t just be caught in human-built reservoirs, because they would fill up and there would be no way to control flooding if more precipitation fell.
A year without snow can be a bad thing. But what might be worse is when the snow melts too early, as it did this year in Arizona and New Mexico. February and March have been warm across the Southwest and the pack has been “completely lost,” Rippey said.
Spring, at least the warm temperatures associated with the season, is coming a week or two sooner in the mountains than it did in the 1950s because of a changing climate, Kapnick said.
“The fact the snowpack is melting earlier means less of it is stored for later on in the season,” she said. “If water falling from the sky fell as rain instead of snow, we would lose that natural reservoir.”
This complicates the life of city and state water managers and can dash the hopes of farmers who see the promises of a snowcapped mountain melt away.
For this year, though, for most of the West, the news is better than it has been, Rippey said. It may just be an average year, but “it is the best thing they have seen since 2011.”