1. 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

2. 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

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

4. 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

5. 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

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

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

8. 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

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

10. % 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

11. More Frequent Droughts
100 year return interval Drought
RCP
200 %
100 %
Swain et al., 2018

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

13. Temperature Exacerbates Drought
% Change in top layer of soil moisture
End of Century ( )*
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
Pierce et al., 2018, California’s Fourth Climate Change Assessment.

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

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

16. 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?