Thanks in large measure to warming temperatures, the average snowpack in U.S. western states has dropped by 15 to 30 percent since 1915.

The water in that lost snowpack is comparable in volume to Lake Mead. With a maximum capacity of 9.3 trillion gallons, Mead is the West’s largest manmade reservoir.

The new data on snowpack declines are among the striking results of a study led by Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University. As part