The Unprecedented Character of California's 20th Century Enhanced Hydroclimatic Variability in a 600-Year Context

Recently, year-to-year swings in California winter precipitation extremes have resulted in drought, wildfires, and floods causing billions of dollars in damage. These recent precipitation swings represent an increasing trend in variability of California's hydroclimate over the past decades. Here, we put this trend in a longer-term context using tree-ring-based precipitation, streamflow, and snow water equivalent reconstructions. We show that the statewide rise in hydroclimate variability in the 20th century is driven by an increasing trend in the magnitude of wet extremes. A prior period of strong variability in the 16th century, in contrast, is related to an increasing trend in the magnitude of dry extremes. Our results are consistent with climate model simulations that suggest an increasingly volatile future for California's hydroclimate and highlight the importance of collaboration between scientists and water resource managers to incorporate this increased variability into their decision-making and planning, acknowledging higher risks for compound events.

Automated summary

Year-to-year swings in winter precipitation extremes in California have caused significant damage through droughts, wildfires, and floods. Using tree-ring-based reconstructions, this study reveals a long-term trend of increasing hydroclimate variability in California, driven by rising magnitudes of wet and dry extremes in the 20th and 16th centuries respectively. These findings align with climate model simulations, emphasizing the need for collaboration between scientists and water resource managers in order to incorporate the increased variability and higher risks of compound events into decision-making and planning processes.