UPDATE ON REGIONAL CLIMATE DOWNSCALING

1. UPDATE ON REGIONAL CLIMATE DOWNSCALING Filippo Giorgi Abdus Salam ICTP, Trieste, Italy JSC Meeting, Arcachon, France, 31 March – 4 April 2008

2. Techniques for simulating high resolution regional climate(Regional Climate Downscaling RCD) • Uniform high resolution AGCM time-slices • Variable resolution AGCMs (or VarGCMs) • Limited area Regional Climate Models (RCMs) • Statistical downscaling (SD) methods The interest in the use of RCD techniques has tremendously increased because of the need of high resolution climate information for impact and adaptation work

3. Time slice AGCMs and VarGCMs • Uniform high resolution time-slice AGCMs • Most AOGCM time slice experiments to date performed at ~50-100 km grid interval • Some experiments available down to 20 km grid interval • Efforts under way to develop cloud resolving global AGCMs • VarGCMs • Regional resolution down to a few tens of km • Stretched grid global modeling project: SGMIP (Stretched Grid Model Intercomparison Project; Fox-Rabinowitz et al. JGR 2006) with four models participating (CSIRO C-CAM; Env.-Canada GEM; Meteo-France ARPEGE; NASA-GSFC GEO-3)

4. Regional Climate Models (RCMs) • Present status of RCMs • A number of RCMs are today available; some of them are “portable” and used by wide communities (e.g. RegCM, PRECIS, RSM,WRF) • Current “state-of-the-art” grid spacing is 10-30 km (higher for a few models); • RCMs are being upgraded to non-hydrostatic, cloud-resolving frameworks in order to go to sub-10 km resolutions • Decadal to centennial simulations have become the “accepted standard” • Virtually all regions of the World have been simulated • A number of review/guidance papers and reports are available • Two-Way nesting • Encouraging results from first experiments • Coupled RCMs • Several coupled RCM efforts under way, including atmosphere, ocean, aerosol, and biosphere components • New emerging areas of application • Seasonal prediction • Impacts

5. Observed Dx = 50 km Dx = 25 km Dx = 12 km RCM simulation of precipitation at different resolutions over the Alps (HadAM3H “driver”) Mean annual precipitation (mm/day) From Christensen et al. 2005

6. CRU obs GCM (FVGCM) DJF precipitation 30-year nested RCM simulation, 1961-1990, 20 km grid spacing RCM (RegCM)

7. Observed Precipitation JJA precipitation 30-year nested RCM simulation, 1961-1990, 20 km grid spacing FVGCM Precipitation RCM Precipitation

8. WINTER DAILY RAINFALL OVER THE ALPS Resolution yields a much better description of extremes

9. Simulation of extreme precipitation Summer 1993 Flood Summer 1993 Flood RegCM3 Observations Summer 1988 Drought Summer 1988 Drought RegCM3 Observations

10. Days with Tmax > 35C Days with Tmin > 20C High danger heat index Application of RCMs to impacts studies Health impacts Increase of heat-related stress over the Mediterranean Diffenbaugh et al. (2007)

11. Simulated Precipitation No-Dust minus Dust Precipitation, CRU (1961-1990) – (1901-1980) Application of RCMs to study chemistry/aerosol-climate interactions Change in peak summer Ozone concentration due to climate change (Meleux et al. 2007) (Konare et al. 2008)

12. Regional intercomparison studies ARCMIP PRUDENCE ENSEMBLES NEWBALTIC PIRCS NARCCAP SGMIP RMIP AMMA AFRMIP AIACC PLATIN ARC Transferability project

13. Statistical downscaling • Use of SD techniques for climate change impact applications has increased considerably due to their computational efficiency • Many different techniques utilizing very different methodologies are available, often tailored to local specific issues • Progress difficult to assess because of the differences across techniques, although SD models are improving • Coordinated projects have been carried out or are under way • STARDEX, MICE, PRUDENCE, ENSEMBLES, AIACC

14. Empirically downscaled precipitation change from different AOGCM simulations

15. Use of RCD tools in developing countries Local scientists could help formulate developing country perspective on climate change by conducting regional climate model experiments Development of portable models for different needs (RegCM, PRECIS, RSM) ICTP-WCRP workshop in Trieste, March 2007

16. Issues emerged from the Trieste workshop • Should we create a “WGRCC”-like panel to oversee and optimize regional climate change research (not just RCM)? • Mandate to be developed by consultation with the scientific community • Creation of a coordinating framework for regional climate change research and simulation • Something along the lines of AMIP/CMIP • Better mechanisms for broadcasting and using RCD information (e.g. for input to AR5) • Develop a sense of ownership by widespread direct participation, especially by developing country scientists • Create stronger communication with the end-user community (impacts, adaptation, mitigation) • Create stronger ties with the global model community • Facilitate provision of forcing data • Create a PCMDI-like LBC/output/data center • Facilitate the development of regional observed and model datasets • Coordinate the organization of regular workshops • Two workshops planned in 2008 – Toulouse, Lund

17. THANK YOU