1. Ten-Year Simulations of U.S. Regional Climate Z. Pan, W. J. Gutowski, Jr., R. W. Arritt, E. S. Takle, F. Otieno, C. Anderson, M. Segal Iowa State University J. H. Christensen, O. B. Christensen Danish Meteorological Institute Copenhagen, Denmark START Temperate East Asia Regional Center(February 2000)

2. Outline Overview Overview Comparison with Observations Comparison with Observations  Precipitation  T min, T max Biases as norms for evaluating climate change Biases as norms for evaluating climate change  Precipitation  T min, T max Conclusions Conclusions START Temperate East Asia Regional Center(February 2000)

3. Outline Overview Overview START Temperate East Asia Regional Center(February 2000)

4. Simulations

5. Domain

6. Purpose  Evaluate RCM performance  Compare RCM and GCM projections  Assess U.S. regional climate change uncertainty

7. Outline Overview Comparison with Observations Comparison with Observations  Precipitation  T min, T max START Temperate East Asia Regional Center(February 2000)

8. RegCM2BiasVEMAP JAN JUL 0-2+2 [mm/d] +4+6 - 4

9. Self-Organizing Maps Set of maps Trained to distribution of data Give 2-D projection of higher order map space Show characteristic data structures Are approximately continuous

18. “Robert Johnson” box: (31-35 N, 85-90 W)

20. Precipitation Regions Upper Miss.

21. Range: 600 - 970 mm

22. Range: 650 - 850 mm

23. Range: 590 - 870 mm

24. T min /T max Problem: Model elevations different from observing stations O O O O O

25. T min /T max Problem: Model elevations different from observing stations O O O O “Solution”: Interpolate to common elevation using dT/dz = - 6.5 K/km (common = real world @ 1/2 deg) O

29. +2.5 -2.5 +12.5 -12.5+22.5 [C] 10 Year Mean Maximum Temperature - RegCM2

30. +2.5 -2.5 +12.5 -12.5+22.5 [C] 10 Year Mean Maximum Temperature - DMI

31. +2.5 -2.5 +12.5 -12.5+22.5 [C] 10 Year Mean Minimum Temperature - RegCM2

32. +2.5 -2.5 +12.5 -12.5+22.5 [C] 10 Year Mean Minimum Temperature - DMI

33. Outline Overview Comparison with Observations  Precipitation  T min, T max Biases as norms for evaluating climate change Biases as norms for evaluating climate change  Precipitation  T min, T max START Temperate East Asia Regional Center(February 2000)

34. Reanalysis HadCM Cont/Scen RegCM2 HIRHAM Possible Comparisons? OBS HadCM Cont/Scen Driving Differences

35. Definition of Biases ReanalysisRegCM2OBS RCM (performance) bias

36. ReanalysisRegCM2 HIRHAM Inter-model bias Definition of Biases

37. Reanalysis HadCM RegCM2 Definition of Biases Forcing bias

38. HadCM RegCM2 HadCM Definition of Biases G-R nesting bias

39. HadCM control HadCM scenario RegCM2 Climate Change Change

40. Climate Change P Control Scenario Change

41. Climate Change P Control Scenario Change Max Bias

42. Analysis Regions

43. Seasonal-regional biases P o, P m are observed, model precipitation N is total grids in the region Climate change ratio Definitions

48. Include here Tmin/max transparencies Degree-days Wind power

49. Outline Overview Comparison with Observations  Precipitation  T min, T max Biases as norms for evaluating climate change  Precipitation  T min, T max Conclusions Conclusions START Temperate East Asia Regional Center(February 2000)

50. Conclusions RegCM2 simulates broad-scale regional features fairly well. Interannual variability in RegCM2 (and HIRHAM) is less than observed. Specific regions and seasons pose special challenge to RegCM2, e.g., south-central US  Timing of events good  Magnitude poor  Moisture transport problem? START Temperate East Asia Regional Center(February 2000)

51. Climate change is 1-3 times larger than biases in most seasons and regions  summer ratios are always less than 1 Ratio of climate change to biases is especially large in the California region Differences between RCM and GCM imply room for RCMs to add value to GCM simulations START Temperate East Asia Regional Center(February 2000) Conclusions

52. Regional warming signal is less robust than precipitation change Future warming projection has large inter-model differences Warming greater for T min than T max Warming greater for winter than summer START Temperate East Asia Regional Center(February 2000) Conclusions

53. Acknowledgments Primary Funding: Electric Power Research Institute (EPRI) Additional Support: U.S. National Oceanic and Atmospheric Administration U.S. National Science Foundation START Temperate East Asia Regional Center(February 2000)

54. EXTRA SLIDES

55. Definition of Biases RCM (performance) bias - difference between reanalysis-driven RCM simulation and observations forcing bias - difference between runs driven by GCM control climate and driven by reanalysis inter-model bias - difference between runs from different RCMs (HIRHAM minus RegCM2), both driven by reanalysis G-R nesting bias – difference between GCM run and RCM run driven by GCM output, both for current climate.