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

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

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

Observed Data

•  U.S. Climate Division Precipitation from Vose et al. 2014

•  SST from Hurrell et al. 2008

4

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

Define ENSO Events •  Centered On December-February Season •  ENSO Category Definition

•  VS El Niño: Niño3.4 > 2.0˚C •  MS El Niño: 2.0˚C > Niño3.4 > 1.0˚C

6

Category January of Season

VS El Niño 1983, 1998

MS El Niño 1897, 1900, 1903, 1912, 1919, 1926, 1931, 1941, 1958, 1966, 1973, 1987, 1992, 1995, 2003, 2010

SST Anomalies During VS and MS El Niño Are Different

7

Average SST Anomaly During VS and MS El Niño

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

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

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

VS El Niño Shifts the

Rainfall Odds Regionally

0 100 200 300 400

0.000

0.005

0.010

0.015

VS El NinoMS El NinoMS OBSNeutral ENSO

Multimodel California Nov Apr PDF(a) North

% of Neutral

Freq

uenc

y

0 100 200 300 400

0.000

0.005

0.010

0.015

(b) Central

% of Neutral

Freq

uenc

y

0 100 200 300 400

0.000

0.005

0.010

0.015

(c) South

% of Neutral

Freq

uenc

y

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

VS El Niño Shifts the

Rainfall Odds Regionally

0 100 200 300 400

0.000

0.005

0.010

0.015

VS El NinoMS El NinoMS OBSNeutral ENSO

Multimodel California Nov Apr PDF(a) North

% of Neutral

Freq

uenc

y

0 100 200 300 400

0.000

0.005

0.010

0.015

(b) Central

% of Neutral

Freq

uenc

y

0 100 200 300 400

0.000

0.005

0.010

0.015

(c) South

% of Neutral

Freq

uenc

y

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

VS El Niño Nearly Eliminates Odds of

Below Average Rainfall

0 100 200 300 400

0.0

0.2

0.4

0.6

0.8

1.0

Prob

abilit

y

VS El NinoMS El NinoMS OBSNeutral

Multimodel California Nov Apr CDF(a) North

% of Neutral

0 100 200 300 400

0.0

0.2

0.4

0.6

0.8

1.0

Prob

abilit

y

(b) Central

% of Neutral

0 100 200 300 400

0.0

0.2

0.4

0.6

0.8

1.0

Prob

abilit

y

(c) South

% of Neutral

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

Midseason Maximum During VS El Niño

14

Monthly Model Simulation Precipitation During VS El Niño

Late Season Maximum During MS El Niño

15

Monthly Model Simulation Precipitation During MS El Niño

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