Atmospheric rivers and flooding in California: a paleo perspective

Atmospheric rivers are associated with some of the largest flood-producing precipitation events in western North America, particularly California. Insight into past extreme precipitation can be reconstructed from sedimentary archives on millennial timescales. Here we document past atmospheric river activity at two lake sites in California - Leonard Lake and Wildcat Lake - using a key metric of atmospheric river intensity called integrated vapor transport (IVT, kg m -1 s -1 ). Specifically, we leverage the positive and significant correlations between lake sediment layers enriched with silicon/aluminum (Leonard Lake) and titanium/aluminum (Wildcat Lake) with modern records of IVT. At the relatively undisturbed site Leonard Lake, the late twentieth century had the highest median IVT since the onset of the Medieval Climate Anomaly (~950 CE), with IVT increasing during the Little Ice Age (~1500-1800 CE). The reconstruction suggests northern California has recently experienced pluvial episodes that exceeded any in the meteorologic instrumental era, with the largest episodes occurring 2,000 and 3,000 years ago. Additional research to corroborate findings from Leonard Lake with sedimentary data from Wildcat Lake are promising. Despite the land-use change near Wildcat Lake, geochemical data indicate intense and long-lasting AR storms are identifiable in this sedimentary record. Take together, these results provide data to help avoid underestimation of potential risks from extreme precipitation and to aid management of water infrastructure.

Speaker: Clarke Knight, US Geological Survey