A Medieval Perspective of Historical California and Nevada Droughts

Abstract:

Dryland closed basin lake systems are ideal natural laboratories for model-proxy evaluations of how climate change alters the regional water balance. We use an existing water balance and lake-evaporation model of the Walker Lake Basin, a 1600-year reconstruction of Walker Lake shoreline elevations, and fields from the 20th Century Reanalysis to provide the following insights: 1) The three major historical (post-Little Ice Age) droughts observed in the California-western Nevada region (the 1930s, 1987-1992, and 2012-2015) are comparable in magnitude to the severe droughts of the Medieval Climate Anomaly but not in duration; 2) The atmospheric circulation anomalies associated with these events include poleward deflections of storm tracks and reduced moisture transport into the region; 3) To produce the Medieval lowstands of Walker Lake, precipitation and circulation anomalies comparable to historical droughts must persist for a minimum of 50 years. These insights show how severe historical and ongoing droughts in this region are within the range of natural variability. The 2012-2015 drought is also shown to be exacerbated by recent positive temperature anomalies that may be outside of the range of natural variability. These results can help to improve future water resource planning for the western United States, where ongoing and future changes in climate leading to increased water scarcity will have significant negative impacts on socioeconomic and ecological systems.