Some Scale Considerations for Predicting/Projecting Extreme Precipitation

WCRP Metrics/Methodologies for ExtremesWCRP Metrics/Methodologies for Extremes September 2010September 2010

Based in part on …

Some Scale Considerations for Some Scale Considerations for Predicting/Projecting Extreme Predicting/Projecting Extreme

PrecipitationPrecipitation

William J. Gutowski, Jr.William J. Gutowski, Jr.Iowa State University Iowa State University

U.S.A.U.S.A.


Methodologies for Estimating ExtremesMethodologies for Estimating Extremes

Simulated time & space scalesSimulated time & space scales

Process behavior under climate changeProcess behavior under climate change


Cold Half of Year

95%

Precipitation:Precipitation:Frequency vs. IntensityFrequency vs. Intensity

~~ Averaging Time Averaging Time

(Gutowski et al. 2003)(Gutowski et al. 2003)

6-hourly

daily

10-day

Simulation:Simulation:

Continental U.S.Continental U.S.

1979-19881979-1988

50-km grid50-km grid

NCEP Reanalysis 1NCEP Reanalysis 1

Analysis:Analysis:

Central U.S.Central U.S.

8 years of 8 years of

October - October - March March

April - May April - May

95%

Warm Half of Year


Precipitation:Precipitation:Frequency vs. IntensityFrequency vs. Intensity

~~ Spatial Scale Spatial Scale

Simulation:Simulation:

Continental U.S.Continental U.S.

1979-19881979-1988

50-km grid50-km grid

Analysis:Analysis:

Central U.S.Central U.S.

8 years of October - 8 years of October - March March


[km]


NARCCAP SimulationsNARCCAP Simulations

• DomainDomain

- Most of North America- Most of North America

• ResolutionResolution

~ 50 km~ 50 km

• Simulation PeriodSimulation Period

- 1978-2004- 1978-2004

• Boundary ConditionsBoundary Conditions

- NCEP/DOE reanalysis- NCEP/DOE reanalysis

MM5MM5Iowa Iowa

State/State/PNNLPNNL

RegCM3RegCM3UC Santa CruzUC Santa Cruz

ICTPICTP

CRCMCRCMQuebec,Quebec,OuranosOuranos

HADRM3HADRM3Hadley CentreHadley Centre

RSMRSMScrippsScripps

WRFWRFNCAR/NCAR/PNNLPNNL

PLUS:GFDL Atmosphere GCM- 0.5˚ resolution- specified SST/ice for same period

NCAR CCSM Atmosphere-Ocean GCM- 1.4˚ (T85) resolution- analysis for same period


Comparison with Comparison with observationsobservations

• Observation-based FieldsObservation-based Fields Precip: University of Washington VIC retrospective analysisPrecip: University of Washington VIC retrospective analysis

Other fields: North American Regional ReanalysisOther fields: North American Regional Reanalysis

• Comparison period: 1982 -1999Comparison period: 1982 -1999 1979-1981 omitted - spinup1979-1981 omitted - spinup UW data end in mid-2000UW data end in mid-2000

• AnalysisAnalysis ““Precipitation event” = Daily precip ≥ 2.5 mm at a grid pointPrecipitation event” = Daily precip ≥ 2.5 mm at a grid point Focus on precip intensity ≥ 99.5% Focus on precip intensity ≥ 99.5%


Regions AnalyzedRegions Analyzed

Boreal forest

Pacific coast

California coast

Great LakesMaritimes

Upper Mississippi

River

Deep South


Precipitation Frequency vs. IntensityPrecipitation Frequency vs. Intensity

99.5%


Days with Simultaneous Extremes on Days with Simultaneous Extremes on “N” Grid Points“N” Grid Points

“widespread extremes”


Composite Structure of Extreme Events - DJFComposite Structure of Extreme Events - DJF


Present & Future Climate – Earlier ResultsPresent & Future Climate – Earlier Results

Control-driven

NCEP-driven Scenario-driven

500 hPa Heights



Precipitation Changes?Precipitation Changes?

Future – CurrentFuture – Current

0.05% Threshold0.05% Threshold + 17% + 17%

Extreme Precip. Extreme Precip. + 26%+ 26%

Extreme precipitation as max humidity

Max atmospheric humidity ~ 7% per degree

Projected temperature increase: ~ 2.5˚C


Africa: Water Balance ChangesAfrica: Water Balance Changes(IPCC AR4 WG1)(IPCC AR4 WG1)

2080-2099 Minus 1980-19992080-2099 Minus 1980-1999 # models with # models with > 0 > 0


Africa: Africa: Precipitation via Statistical Downscaling Precipitation via Statistical Downscaling

2070-20992070-2099

VsVs

30-yr pres30-yr pres

2080-20992080-2099

vs.vs.

30-yr pres30-yr pres

Range: Range:

[-80,+80] [-80,+80] mm/monthmm/month

(Hewitson & (Hewitson & Crane, 2006)Crane, 2006)


Higher resolution is necessary, but not sufficient, for Higher resolution is necessary, but not sufficient, for simulating short-term (e.g., daily) precipitation simulating short-term (e.g., daily) precipitation extremes.extremes.

Coarser models (and nudged regional models) tend to Coarser models (and nudged regional models) tend to have daily extremes covering a wider area than have daily extremes covering a wider area than observed extremes. observed extremes.

Focusing on environments conducive to extremes Focusing on environments conducive to extremes yields relevant climatic behavior, even in relatively yields relevant climatic behavior, even in relatively coarse models.coarse models. This conclusion rests on the assumption that important This conclusion rests on the assumption that important

small-scale features are not missing (e.g., low-level small-scale features are not missing (e.g., low-level jets).jets).


Thank You!Thank You!

Some Scale Considerations for Predicting/Projecting Extreme Precipitation

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