On The Unprecedented Character Of Enhanced Hydroclimate Variability In California Over The Past 600 Years
Presenter: Diana Zamora-Reyes1
Co-Author(s): Bryan Black
Advisor(s): Dr. Valerie Trouet
1Department of Hydrology and Atmospheric Sciences, University of Arizona
Most of the precipitation over California occurs in a short window of time from November to March and is highly dependent on the frequency of winter storms steered towards the state. The amount of precipitation thus tends to vary from year to year, which was evident in the recent (2012-2017) extremely dry-to-extremely wet cycle that resulted in drought, wildfires, and floods throughout California and caused more than $6 billion in damage. In 2015, the Sierra Nevada snowpack reached a 500-year low due to below average precipitation and above average temperatures, while in 2017 the snowpack was above average due to record-high precipitation totals and a series of rain-on-snow events almost led Oroville Dam to collapse. Here, we examine whether this extreme-to-extreme pattern is exceptional in the context of the past 600 years. Instrumental precipitation and streamflow data (1940-2019) show that northern and southern California have an increasing trend in variability starting in the 1950s that is primarily caused by larger wet extremes. We have extended these results using 30 tree-ring based hydroclimate reconstructions throughout the state. We show that the variability seen in the instrumental records over southern and northern California has reached unprecedented levels over the past 600 years. Our results are consistent with climate model simulations that suggest an increasingly volatile future. Water resources managers will need to incorporate this increased variability into their planning for public and agricultural water supply, while being aware of the higher risks for wildfires and floods.