During droughts, groundwater pumping is increased to make up for losses from surface water. This is especially true in California’s Central Valley, which stretches roughly 400 miles from Redding to just south of Bakersfield, and is the heart of the state’s $47 billion-a-year agricultural industry. For decades, many parts of the Central Valley aquifer have been overdrafted, but recent work by scientists from the University of California, Los Angeles, and the University of Houston have attempted to put a more precise number on how much water is being pumped.