A drought in California affects much of the western United States. From 2011 to 2015, there was little rain and snow in much of the region, but that was just part of the problem. These areas also experienced record-high heat, which baked away what little moisture remained in the soil. … One study from the University of Minnesota and the Woods Hole Oceanographic Institution found it’s the worst drought in 1,200 years. …To get historical data about past dry years, we can use data from the National Oceanic and Atmospheric Administration and a computer climate model called the North American Drought Atlas.