Does El Niño Intensity Matter for California...
Transcript of Does El Niño Intensity Matter for California...
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?
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Observed Data
• U.S. Climate Division Precipitation from Vose et al. 2014
• SST from Hurrell et al. 2008
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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
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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
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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
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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
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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
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Monthly Model Simulation Precipitation During VS El Niño
Late Season Maximum During MS El Niño
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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
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