We Californians know the weather has been dry, but exactly how dry? B. Lynn Ingram and Frances Malamud-Roam, authors of The West Without Water, provide some historical context for the current drought in Monday’s Los Angeles Times. Ingram and Malamud-Roam look back further than the 119 years of climate data we have on record for California, to the geologic past. Measuring tree ring patterns throughout the Western United States, the authors determined that the last drought this severe occurred in AD 1580. If our current water shortage continues apace, we will have had the driest year in half a millennium.