1. Does El Niño Intensity Matter for California Precipitation? Andy Hoell*, Marty Hoerling*, Jon Eischeid* #, Klaus Wolter* #, Randy Dole *, Judith Perlwitz* #, Taiyi Xu* #, Linyin Cheng* # * NOAA/ESRL/PSD # CIRES/Univ. Colorado-Boulder

2. CA Rainfall During El Niño Is Mixed Statewide Wet During the Two VS El Niño Statewide Wet During Half MS El Niño 2 Nov-Apr 1896-2014 Statewide Precipitation VS El Niño * = MS El Niño

3. Questions 1.Is statewide November-April California wet symptomatic of the sensitivity to sea surface temperature (SST) forcing during very strong (VS) El Niño? 2.Is there a difference in impacts of VS El Niño and moderate-to-strong (MS) El Niño? 3.How do risks for wet vs. dry rainy season conditions change with El Niño? 3

4. Observed Data U.S. Climate Division Precipitation from Vose et al. 2014 Precipitation composites and distribution functions SST from Hurrell et al. 2008 SST composites, SST & sea ice ocean boundary conditions in AMIP simulations 4

5. Model Simulations Driven by observed monthly time-varying SST, sea ice, greenhouse gases and ozone for 1979- 2014 Three models and 130 ensembles CAM5 – 50 ensembles GFSv2 – 50 ensembles ECHAM5 – 30 ensembles Aggregate all ensemble members All models simulate similar regional California precipitation during ENSO 5

6. Define ENSO Events Centered On December-February Season ENSO Category Definition VS El Niño: Niño3.4 > 2.5˚C MS El Niño: 2.0˚C > Niño3.4 > 1.0˚C 6 CategoryJanuary of Season (Niño3.4 Index) VS El Niño 1983 (2.7), 1998 (2.5) MS El Niño 1897 (1.4), 1900 (1.4), 1903 (1.3), 1912 (1.1), 1919 (1.4), 1926 (1.5), 1931 (1.4), 1941 (1.4), 1958 (1.4), 1966 (1.2), 1973 (1.7), 1987 (1.3), 1992 (1.9), 1995 (1.1), 2003 (1.2), 2010 (1.5)

7. SST Anomalies During VS and MS El Niño Are Different 7 Average SST Anomaly During VS and MS El Niño

8. Strong Regional Rainfall Changes With VS El Niño 8 Nov-Apr Precipitation During El Niño North and Central California sensitive to VS El Niño only Observed

9. Strong Regional Rainfall Changes With VS El Niño 9 Nov-Apr Precipitation During El Niño North and Central California sensitive to VS El Niño only Observed Simulated

10. 10 Nov-Apr Precipitation During El Niño Strong Regional Rainfall Changes With VS El Niño Southwest U.S. more sensitive to VS than MS El Niño Observed Simulated

11. VS El Niño Shifts the Rainfall Odds Regionally 11 Nov-Apr PDF During El Niño North and Central California sensitive to VS El Niño only Overall shift to statewide wet conditions during VS El Niño

12. VS El Niño Shifts the Rainfall Odds Regionally 12 Nov-Apr PDF During El Niño North and Central California sensitive to VS El Niño only Overall shift to statewide wet conditions during VS El Niño

13. VS El Niño Nearly Eliminates Odds of Below Average Rainfall 13 Nov-Apr CDF During El Niño VS El Niño-driven regional below average rain is 5% VS El Niño significantly increases regional odds of 150% and 200% of normal 35% 60% 70%

14. Midseason Maximum During VS El Niño 14 Monthly Simulated Precipitation During VS El Niño

15. Late Season Maximum During MS El Niño 15 Monthly Simulated Precipitation During MS El Niño

16. Questions 1.Is statewide California November-April wet symptomatic of the sensitivity to sea surface temperature (SST) forcing during very strong (VS) El Niño? VS El Niño forces in excess of 130% of average precipitation 2.Is there a difference in impacts of VS El Niño and moderate-to-strong (MS) El Niño? North and Central California is sensitive to only VS El Niño 3.How do risks for wet vs. dry rainy season conditions change with El Niño? VS El Niño nearly eliminates the odds of below average November-April rainfall 16

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