Atmospheric rivers (ARs) are major drivers of precipitation in western North America, particularly California. This study reconstructs AR activity near Leonard Lake, California, over the past 3,200 years using silicon/aluminum (Si/Al) enriched layers in lake sediments, a proxy highly correlated with modern integrated vapor transport (IVT). The reconstruction reveals that late Holocene California experienced pluvial episodes exceeding the instrumental era's range, with the most intense events occurring two to three millennia ago. The late 20th century shows the highest median IVT since the Medieval Climate Anomaly, with increased IVT during the Little Ice Age. These findings highlight the underestimation of potential risks from extreme precipitation and underscore the need for improved future planning.

Clarke A. Knight, Lysanna Anderson, Liubov Presnetsova, Marie Champagne, David Wahl