It has lasted longer than the Dust Bowl of the 1930s. It’s dropped water levels perilously low at two of the nation’s largest reservoirs, forced ranchers to sell off herds and helped propel scorching wildfires. And worst of all, the drought blanketing the western United States is not going away. A group of experts featuring federal and state officials and farmers and ranchers spent nearly three hours yesterday chronicling the devastation caused by drought conditions that now cover almost every inch of seven Western states. Half of the U.S. population lives in a drought-stricken area.