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

• Published in: Geophysical research letters 2022-10, Vol.49 (19), p.n/a
• Main Authors: Zamora‐Reyes, Diana, Broadman, Ellie, Bigio, Erica, Black, Bryan, Meko, David, Woodhouse, Connie A., Trouet, Valerie
• Format: Article
• Language: English
• Subjects: 16th century; 20th century; California; Climate models; Climate variability; Context; Decision making; Drought; Extreme values; Extreme weather; extremes; Flood damage; Government; Hydroclimate; Mediterranean climate; Precipitation; Rainfall; River flow; Rivers; Scientists; Snow; Snow-water equivalent; Stream discharge; Stream flow; Variability; Water resources; Water resources management; Wildfires; Winter precipitation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099582

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. Plain Language Summary California's lack, as well as surplus, of rain has been in the news recently. Due to its Mediterranean climate, the state receives most of its rainfall from November to March and the amount varies from year to year. However, this variability has been increasing over the past decades in both rainfall and river flow. This study aims to place this 20th century increasing variability in a longer‐term perspective using tree‐ring records. We show that this statewide positive trend in variability of California's rainfall, river flow, and snow during the 20th century is caused by an increase in the magnitude of very wet years, which is a pattern that has not been seen in the past 600 years. We also show that the 16th century is another period with statewide increased variability that is caused by dry years getting drier. These results enhance our understanding of the 20th century rise in variability, which is expected to continue in the future, and highlights the need for scientists to work with local, state, and federal agencies to address this climatic variability in their decision‐making process. Key Points California's hydroclimate shows enhanced variability caused by increasingly wet extremes during the 20th century Tree‐ring based hydroclimate reconstructions suggest that this statewide configuration has not been seen in the past 600 years The 16th century shows enhanced hydroclim