Water securitySierra snowpack could drop by nearly 80% by end of century

A future warmer world will almost certainly feature a decline in fresh water from the Sierra Nevada mountain snowpack. Now a new study by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) that analyzed the headwater regions of California’s 10 major reservoirs, representing nearly half of the state’s surface storage, found they could see on average a 79 percent drop in peak snowpack water volume by 2100.

What’s more, the study found that peak timing, which has historically been April 1, could move up by as much as four weeks, meaning snow will melt earlier, thus increasing the time lag between when water is available and when it is most in demand.

LBL says that the article, published recently in the journal Geophysical Research Letters, aims to answer when and how the snowpack and snow melt will change – including whether there are variations by region or elevation – by analyzing climate simulations at mid-century and the end of the century across five different regional climate models.

“This study is unique in that we’re sampling across a community of models so we can see if models disagree at mid-century and end of century across a number of different snowpack measures, such as peak timing, total water volume, and melt rate,” said Alan Rhoades, a Berkeley Lab postdoctoral fellow and lead author of the study. “What we found is the models usually disagree more at mid-century, but by end century they are pretty much in unison with another that under a high-emissions scenario there will be a dramatic decline in Sierra Nevada snowpack by 2100.”

What was also distinctive about this research is that the scientists worked directly with water managers with the aim of producing “actionable science.” That included getting feedback from water managers on what metrics would be most useful for resource planning purposes.

“Water managers are constantly competing between how much flood risk can they handle with reservoir storage and how much supply they can provide for urban and agricultural users,“ Rhoades said. “We engage with them, and say, hey, is this a useful way to look at mountain snowpack issues?”