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Overview of Hybrid Delta vs WRF Downscaling Approaches

Overview of Hybrid Delta vs WRF Downscaling Approaches. Hybrid Delta Downscaling Method. Performed for each VIC grid cell:. Bias Corrected Future Monthly CDF. Hist. Daily Timeseries. 30 yr window. 1916-2006. Projected Daily Timeseries. Historic Monthly CDF. Hist. Monthly

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Overview of Hybrid Delta vs WRF Downscaling Approaches

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  1. Overview of Hybrid Delta vs WRF Downscaling Approaches

  2. Hybrid Delta Downscaling Method • Performed for each VIC grid cell: Bias Corrected Future Monthly CDF Hist. Daily Timeseries 30 yr window 1916-2006 Projected Daily Timeseries Historic Monthly CDF Hist. Monthly Timeseries 1916-2006 1970-1999 1916-2006 “Base Case”

  3. Monthly to Daily Precipitation Scaling SeaTac. Feb, 1996, hypothetical 30% Increase Daily Precipitation (mm) Day of Month

  4. WRF Daily Downscaling Method • WRF output is first regridded to 1/16th degree • Then, for each VIC grid cell: Historical VIC Daily CDF 1970-1999 Bias Corrected Daily Time Series WRF Daily CDF WRF Daily Time Series 1970-1999 2040-2069 1970-1999 1970-1999 2040-2069 The storm size distribution and time series behavior of the simulations comes directly from the daily WRF simulations.

  5. Bias Correcting WRF Simulations of PNW Climate

  6. Pre-Processing and Bias Correction • Methodology • 30-year study periods • WRF to daily forcing • Interpolate from 1/8 to 1/16 degree grid • bias correction of daily data by month • Testing and Analysis • PNW Domain Maps • Extremes, statistics • Relative change • Mean, Variance • Quanitles • Cell CDFs, time series • Lumped statistics • Monthly • Elevation / aspect • Geography* • Basin • Mountain range

  7. 30-year Study Periods

  8. Combining WRF runs into 30-year epochs 2000 1970 1990 1980 • 1970-2000 (1980s) • 2010-2040 (2020s) • 2040-2070 (2050s) • Convert 6 hour WRF output to daily. • Precipitation (cumulative to incremental) • Temperature (maximum/minimum) • Wind (average) 1970s 1980ss 1990s Omitted model output Included model output Temporal boundary

  9. Bias Correction • Create monthly data collections • Generate quantile maps • Training Period (1980s) • Observed • Simulated • Future Periods (2020s, 2050s) • Simulated • Bias Correct • By lookup • By extrapolation • Extrapolation • Precip • Scale historic observed mean by ratio of future WRF value to WRF training period mean • Temperature • Subtract offset in means of future and training period WRF simulations • Bias correct by anomaly but if no mapping then just use (WRF future value less WRF base mean) • Add offset to give future bias corrected value

  10. CDFs and Accumulated Time Series for Precip: Mar, Jul

  11. Temperature CDF (Jan, Aug)

  12. Lumped Statistics and Maps • Character of trends is complex due to variation seasonally and spatially. • Initial characterization using WA Cascades • 46-49N, 122-120W • Rainfall • Increased: Nov (PNW) • Decreased: Dec. (western WA) • E. Oregon: • Jan/Mar N-S increase switch • Temperature • Appox. 2+ degree by 2050s • More warming in higher elevations

  13. 2050s Precipitation: q10 Percent Change Dec Nov Mar Jan

  14. Elevation banded WA Cascades 2020s and 2050s monthly mean (Tmax, P) changes from 1980s Low < 250 m Middle < 500 m High < 1k m

  15. Elevation banded WA Cascades 2020s and 2050s monthly q10 (Tmax, P) changes from 1980s Low < 250 m Middle < 500 m High < 1k m

  16. Maximum Precipitation 1980s 2020s 2050s

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