PORTLAND, Ore.—Scientists have found dramatically declining snowpack across the American West over the past six decades that will likely cause water shortages in the region that cannot be managed by building new reservoirs, according to a study published Friday.

The study led by scientists from Oregon State University and the University of California, Los Angeles found drops in snow measurements at more than 90 percent of regional snow monitoring sites that have consistently tracked snow levels since 1955, said Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University.

Study authors also used modeling to show the average snowpack in the region dropped between 15 and 30 percent in a little more than a century, he said, and that modeling paralleled the actual findings based on existing measurements.

That means the region’s average snowpack has lost the equivalent volume of water that it would take to fill Lake Mead, the West’s largest man-made reservoir, Mote said.

The study appeared in NPJ Climate and Atmospheric Science and was a follow-up study to one completed in 2005. This analysis found the loss of snowpack has accelerated, Mote said.

“It’s a bigger decline than we expected,” he said. “In many lower-elevation sites, what used to fall as snow is now rain. Upper elevations have not been affected nearly as much, but most states don’t have that much area at 7,000-plus feet.”

The amount of water stored in the region’s snowpack is roughly the same as all the water stored in the region’s reservoirs, he said.

“The solution isn’t in infrastructure. New reservoirs could not be built fast enough to offset the loss of snow storage,” Mote said.

The study found California had the most gains in snowpack since 1955, but recent droughts erased those gains and caused the snowpack to fall in many locations.

Eastern Oregon and northern Nevada saw the worst decreases in snowpack over the span of the study.

Individual sites in California, Montana, Idaho, Washington and Arizona saw snowpack declines of more than 70 percent, the study found.

Mote said it’s not snowing less, but that the snow is melting sooner in the season at higher elevations, leading to low levels in river and reservoir levels during the driest days of summer and early fall.

The study focused on data from 1,766 snowpack monitoring sites across the western U.S., most of them tracked by the U.S. Department of Agriculture and the California Department of Water Resources.

Researchers looked at snow measurements taken April 1, which is typically at the height of the snowpack, but also looked at measurements taken in January, February, March and May.

“We found declining trends in all months, states and climates,” Mote said.

Snowpack levels are below average in the western U.S. so far in 2018 as well, he said.

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