Jan 21, 2018

Nevada researchers warn of more ‘snow droughts,’ even in wet years

Sierra Nevada, California
USA
by
Henry Brean
,
Las Vegas Review-Journal
The view from the east side of Washoe Lake on Jan. 7 shows what snow drought looks on Slide Mountain and Mount Rose near Reno. Photo: Benjamin Hatchett, DRI
The view from the east side of Washoe Lake on Jan. 7 shows what snow drought looks on Slide Mountain and Mount Rose near Reno. Photo: Benjamin Hatchett, DRI

Periods of below-average snowpack have become increasingly common in some Western mountain ranges, and more frequent snow droughts are likely as global temperatures continue to rise, according to Benjamin Hatchett, a postdoctoral fellow in meteorology and climatology at the Desert Research Institute in Reno.

Hatchett and fellow DRI climate researcher Daniel McEvoy are studying trends and changes to mountain snowpack and their impact on regional watersheds and the economies in places where winter recreation fuels tourism.

...

In a paper published recently in the journal Earth Interactions, they used hourly, daily and monthly data to analyze the progression of eight historic snow droughts that occurred in the northern Sierra Nevada between 1951 and 2017. What they found were two distinct types of snow drought: the familiar “dry” variety caused by low levels of precipitation and a “wet” drought that results when mountain areas usually blanketed with snow get rain instead.

Hatchett said the most recent drought in the Sierra was “pretty similiar” to previous dry spells in terms of precipitation, “but it was this increase in temperature that really exacerbated the severity.”

“As the climate grows warmer and more precipitation falls as rain instead of snow, we are seeing that we can have an average or above-average precipitation year and still have a well-below-average snowpack,” said Hatchett, who has noticed the difference firsthand over a lifetime of backcountry skiing.

In November, he published research outlining a 1,200-foot rise in the average snow level — the elevation at which rain turns to snow — in the Northern Sierra over the past 10 years. Over that same period, the region was experiencing its warmest decade on record, he said.

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Snowpack is crucial even in communities that rarely see any snow. The Las Vegas Valley draws 90 percent of its water supply from Lake Mead, and nearly all of that water comes from snowmelt in the mountains that feed the Colorado River.

Hatchett said the Colorado is more susceptible to the dry form of snow drought because the mountains that feed the critical watershed are higher and farther inland. The river also benefits from having “a bigger catcher’s mitt” of mountain ranges feeding into it, so it might be dry in some areas but wet in others, he said.

A dam emergency

But Hatchett said warming temperatures also can lead to an increase in so-called “rain-on-snow events,” in which powerful and unseasonably warm rainstorms cause the snowpack to melt all at once. Suddenly, “water is moving through the system very quickly and has to be dealt with as a hazard, not a resource,” he said.