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Some Scale Considerations for Predicting/Projecting Extreme Precipitation

Some Scale Considerations for Predicting/Projecting Extreme Precipitation. William J. Gutowski, Jr. Iowa State University U.S.A. Based in part on …. Methodologies for Estimating Extremes. Simulated time & space scales Process behavior under climate change.

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Some Scale Considerations for Predicting/Projecting Extreme Precipitation

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  1. Some Scale Considerations for Predicting/Projecting Extreme Precipitation William J. Gutowski, Jr. Iowa State University U.S.A. Based in part on …

  2. Methodologies for Estimating Extremes • Simulated time & space scales • Process behavior under climate change

  3. Precipitation:Frequency vs. Intensity~ Averaging Time Cold Half of Year Warm Half of Year 6-hourly Simulation: Continental U.S. 1979-1988 50-km grid NCEP Reanalysis 1 Analysis: Central U.S. 8 years of October - March April - May daily 95% 95% 10-day (Gutowski et al. 2003)

  4. Precipitation:Frequency vs. Intensity~ Spatial Scale Simulation: Continental U.S. 1979-1988 50-km grid Analysis: Central U.S. 8 years of October - March [km] (Gutowski et al. 2003)

  5. NARCCAP Simulations HADRM3 Hadley Centre RegCM3 UC Santa Cruz ICTP RSM Scripps WRF NCAR/ PNNL MM5 Iowa State/ PNNL CRCM Quebec, Ouranos • Domain - Most of North America • Resolution ~ 50 km • Simulation Period - 1978-2004 • Boundary Conditions - NCEP/DOE reanalysis 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

  6. Comparison with observations • Observation-based Fields • Precip: University of Washington VIC retrospective analysis • Other fields: North American Regional Reanalysis • Comparison period: 1982 -1999 • 1979-1981 omitted - spinup • UW data end in mid-2000 • Analysis • “Precipitation event” = Daily precip ≥ 2.5 mm at a grid point • Focus on precip intensity ≥ 99.5%

  7. Regions Analyzed Boreal forest Maritimes Great Lakes Pacific coast Upper Mississippi River Deep South California coast

  8. Precipitation Frequency vs. Intensity 99.5%

  9. Days with Simultaneous Extremes on “N” Grid Points “widespread extremes”

  10. Composite Structure of Extreme Events - DJF

  11. Composite Structure of Extreme Events - DJF

  12. Composite Structure of Extreme Events - DJF

  13. Present & Future Climate – Earlier Results 500 hPa Heights Scenario-driven NCEP-driven Control-driven (Gutowski et al. 2008)

  14. Precipitation Changes? Future – Current 0.05% Threshold + 17% Extreme Precip. + 26% Extreme precipitation  as max humidity  Max atmospheric humidity  ~ 7% per degree Projected temperature increase: ~ 2.5˚C

  15. Africa: Water Balance Changes(IPCC AR4 WG1) # models with  > 0 2080-2099 Minus 1980-1999

  16. Africa:  Precipitation via Statistical Downscaling 2070-2099 Vs 30-yr pres Range: [-80,+80] mm/month 2080-2099 vs. 30-yr pres (Hewitson & Crane, 2006)

  17. Higher resolution is necessary, but not sufficient, for simulating short-term (e.g., daily) precipitation extremes. • Coarser models (and nudged regional models) tend to have daily extremes covering a wider area than observed extremes. • Focusing on environments conducive to extremes yields relevant climatic behavior, even in relatively coarse models. • This conclusion rests on the assumption that important small-scale features are not missing (e.g., low-level jets).

  18. Thank You!

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