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.