California's Drought of the Future: A Midcentury Recreation of the Exceptional Conditions of 2012-2017

The California drought of 2012-2016 was a record-breaking event with extensive social, political, and economic repercussions. The impacts were widespread and exposed the difficulty in preparing for the effects of prolonged dry conditions. Although the lessons from this drought drove important changes to state law and policy, there is little doubt that climate change will only exacerbate future droughts. To understand the character of future drought, this paper examines this recent drought period retrospectively and prospectively, that is, as it occurred historically and if similar dynamical conditions to the historical period were to arise 30 years later (2042-2046) subject to the effects of climate change. Simulations were conducted using the Weather Research and Forecasting model using the pseudo global warming method. The simulated historical and future droughts are contrasted in terms of temperature, precipitation, snowpack, soil moisture, evapotranspiration, and forest health. Overall, the midcentury drought is observed to be significantly worse, with many more extreme heat days, record-low snowpack, increased soil drying, and record-high forest mortality. With these findings in mind, the data sets developed in this study provide a means to structure future drought planning around a drought scenario that is realistic and modeled after a memorable historical analog. Plain Language Summary The California drought of 2012-2016 was notorious for breaking numerous temperature, precipitation, and snowpack records. However, it was also a warning of the types of droughts we are likely to experience in light of climate change. In order to better understand and quantify the characteristics of future drought in California, this study uses a climate modeling technique known as pseudo global warming to simulate a midcentury (2042-2046) drought that is realistic in light of this recent historical analogue. Overall, the midcentury drought is much worse than its historical counterpart, with many more extreme heat days, record-low snowpack, increased soil drying, and record-high forest loss. This study points to the extensive effort that must now be invested on the part of California's residents, water managers, policymakers, and the broader stakeholder community to prepare for the next big drought.