Salt-encrusted soil bakes in the sun in the Colorado River delta. A question has bothered climatologist Park Williams during the decade he’s been probing drought in the Southwest. Like other climate scientists, he knew from research papers and worldwide storm patterns that a warming atmosphere is thirstier and sops up more moisture from oceans and the land. “But, in the Southwest, we've seen the exact opposite happening,” said Williams, an associate professor in the University of California, Los Angeles’ geography department. “For the last 50 or so years, we've actually seen the amount of water vapor molecules in the atmosphere decline” while temperatures have climbed about twice as fast as the global average.