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Scale Considerations for Extreme Precipitation Prediction

Understanding spatial scale impact on extreme precipitation projections. Analyzing simulation data from various models. Discussion on climate change effects. Focus on intensity vs. frequency. Examining regions experiencing extreme events. Future climate scenarios and water balance changes.

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Scale Considerations for Extreme Precipitation Prediction

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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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