California Water Projections: More Extreme Julie Kalansky, David Pierce, Dan Cayan, Laurel Dehaan, Alexander Gershunov, Mike Dettinger* Scripps Institution of Oceanography, *USGS August 28, 2018 CA Adaptation Forum Shasta Dam, 2015 O. Alexandrov

Key Points Current Precipitation Regime Will be More Extreme Precipitation Regime is going to become more variable  Greater climate whiplash More droughts & more extremes precip events MORE VARIABLE PRECIPITATION REGIME Earlier snow melt Less precip in shoulder seasons SEASONAL CHANGES

Greenhouse Gas Scenarios figure courtesy of D. Pierce (Scripps)

CA has highest year-to-year precipitation variability in the US 0.5 means that year to year variability is half of the annual average Dettinger et al. 2011

Extreme Precipitation Events Explain Year-to-Year Variability 85% of the year-to-year variability is explained by 95th percentile storms 85% of the year-to-year variability is explained by 95th percentile storms Two sides to the same coin Dettinger and Cayan, 2014

Atmospheric Rivers (ARs) drive most extremes in CA Precipitable Water; March 20, 2018 UW-CIMSS

More Variability  Greater Climate Whiplash More Precipitation More Variable Berg and Hall 2016

More Variability  Greater Climate Whiplash Dry (20%tile) to wet (80%tile) Whiplash events More Precipitation More Variable Berg and Hall, 2016 Swain et al., 2018

Extremes Will become more Extreme Change in Average Wettest Day per Year D. Pierce inches % change % change

% change in precipitation frequency by intensity bin Extremes Will become more Extreme Change in Average Wettest Day per Year D. Pierce Russian River basin inches % change % change % change in precipitation frequency by intensity bin The changes in the most extreme precipitation is due to increase atmospheric river intensity. Figure courtesy of A. Gershunov and T. Shulgina

More Frequent Droughts 100 year return interval Drought RCP 8.5 2070 - 2100 200 % 100 % Swain et al., 2018

Temperature Exacerbates Drought % Change in top layer of soil moisture End of Century (2070-2100)* RCP 4.5 RCP 8.5 *Relative to historical 1976-2005 Pierce et al., California’s Fourth Climate Change Assessment, 2018.

Temperature Exacerbates Drought % Change in top layer of soil moisture End of Century (2070-2100)* Temperature Impacts Reduced Stream Flows Warmer water temperatures Reduced Run-off Reduced Recharge Less snow, more rain (snow-drought) RCP 4.5 RCP 8.5 *Relative to historical 1976-2005 Pierce et al., 2018, California’s Fourth Climate Change Assessment.

Longer Summer Drought – Drier shoulder Seasons Pierce et al., 2018, California’s Fourth Climate Change Assessment.

Longer Summer Drought – Less Snow & Earlier Melt D. Pierce Pierce et al., 2018, California’s Fourth Climate Change Assessment.

Key Points Current Precipitation Regime Will be More Extreme Precipitation Regime is going to become more variable  Greater climate whiplash More droughts & more extremes precip events MORE VARIABLE PRECIPITATION REGIME Earlier snow melt Less precip in shoulder seasons SEASONAL CHANGES Questions? jkalansky@ucsd.edu