Spring heatwaves deplete the water supply in the Western US

In a new study from the Desert Research Institute, experts have determined that a spring heatwave in April 2021 caused record snow melt across the western United States. This phenomenon disrupted the natural water cycle, and contributed to severe water supply shortages in the region. 

Record-breaking snowmelt rates were documented at nearly 25 percent of all mountain snowpack monitoring sites in the western states. This loss of snow depleted a natural water reservoir that is critically need during the hotter months. 

“One thing that stood out was the spatial pattern. It wasn’t just one single mountain range or one part of the West – there were snowmelt records across the entire Western U.S., in all 11 states,” noted said study co-author Dr. Daniel McEvoy.

The researchers discovered that record snowmelt rates occurred throughout the entire month of April, but two particular heatwaves did the most damage. During the first week of April 2021, temperatures were four to six degrees Celsius above average in the Rocky Mountains. During the third week of April, the Pacific Northwest experienced temperatures up to eight degrees Celsius above average.

“Summer heat waves are studied extensively, but people don’t often care as much about a spring heatwave because the actual air temperatures don’t usually lead to human health impacts,” said Dr. McEvoy. “But at the same time, they are creating these hydrological and climatological extreme impacts.” 

“What really motivated this study was that in May and June of 2021, I kept hearing from other climatologists, meteorologists, hydrologists, and even skiers, that ‘the snow really came off the mountains fast this year. I kept hearing that over and over again.” 

According to Dr. McEvoy, the spring 2021 heatwave was one of several extreme climate events over the course of that year. “There was a compounding set of climate extremes that all contributed to this rapid expansion and intensification of the drought across the Western U.S. during the late spring and summer.” 

The researchers noted that these spring heatwaves are consistent with the long-term trend of spring warming across the West, and that because of this, April 1 may no longer be a reliable benchmark for evaluating snowpack levels and their seasonal contributions to western water supplies. 

Dr. McEvoy said that future research will examine the impacts and frequency of spring heatwaves. “Understanding the predictability of these types of snowmelt events would be helpful for both drought early warning and water resource management,” says McEvoy.  

The study is published in the journal Environmental Research Letters.

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By Chrissy Sexton, Earth.com Editor

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