Lake Sediments Reveal the Long History of California’s Past Droughts

Abstract:

Global warming is changing Earth’s climate. While California will certainly warm, it remains uncertain whether precipitation amounts will increase or decrease. Water shortages, however, are almost certain as the loss of snowpack with rising temperatures reduces water storage and increases flashiness of runoff. Overpopulated and water-stressed, the coastal southwestern United States (_cswUS) already faces a perennial freshwater shortage. Rising temperatures, even without a decrease in precipitation amounts, will stress the region’s socioeconomic stability and water management practices. Critical to planning for and mitigating against future risks from drought in this highly variable climate requires a long perspective, longer than our instrumental records. Here, we present various decadal to multi-decadal resolved lake sediment records from the _cswUS used to reconstruct the history of drought. Importantly, these lake-based reconstructions extend our knowledge of hydroclimatic variability beyond the tree ring records, which, for the _cswUS are rarely longer than 1000 years. Moreover, tree ring records do not cover the driest and low-lying areas of the state where some of our largest cities are found. Our results indicate drought conditions of longer duration than anything observed in the tree-ring records. Regional comparisons indicate also that the tropical Pacific is linked to drought in the study region. Finally, our results highlight the complex relationships between climatic forcings and the region’s hydroclimate, often producing abrupt, sustained change. The paleoclimatic record allows us to study the longer perspective of drought frequency, magnitude, and duration in the context of changing forcings and boundary conditions. Learning from, and planning for, these extreme (paleo)droughts should be an important objective of our state’s water management program.