Regional Climate Modelling in Europe:

Transcription

1 Regional Climate Modelling in Europe: Focus on precipitation Clemens Simmer Meteorologisches Institut Rheinische Friedrich-Wilhelms-Universität Bonn

2 Content Motivation Why do we need Regional Climate Models (RCMs) RCMs used in Europe The German community RCM CCLM Some Predictions for Germany the Consortial Climate Runs some preliminary Results regional studies Conclusions and Outlook

3 Trends in precipitation (Source: IPCC, AR4, p. 254) (Anomalies compared to ) Diversity in estimates due to different sources Strong year to year variations Regionalisation of trends difficult Precipitation is a difficult climate variable

4 Regional Precipitation Trends (IPCC, 2007)

5 Climate Projections Precipitation for year 2100 Northern Winter Northern Summer Hatched: White: 90% of the models coincide in the sign of the trends <66% of the models coincide in the sign of the trends Increase of winter precipitation in Northern Eurasia in Winter Decrease of winter precipitation over the Mediterranian Decrease of Summer precipitation over Southern and Western Europe, Mediterranian, Black Sea and Caspian Sea

6 Why do we need regional climate models? More spatially detailed information about climate projections Better representation of regional and local interactions e.g. with the surface Better representation of precipitation physics in the models Should be better than statistical downscaling because of nonlinear effects in climate change

7 Resolution of RCMs (B. Rockel, GKSS, 2007)

8 How are RCMs built? Derived from Global Climate Models (GCMs) by resolution enhancement nesting procedures non-hydrostatic extensions Derived from NWP-Models by Adding variable CO 2 Adding interactive vegetation and soil Improving on numerical schemes (balance of mass, energy,...)

9 Regional Climate Models (1) Different versions for NWP and CLM (2) Climate mode not yet tested (from Rockel, GKSS, 2007)

10 Regional Climate Models RCMs: ETACLIM REGCM3 Compared against GPCP-Observations Fernandez et al. 2007

11 Temperature from RCMs Difference of annual means from observations BIAS from from -1.4 to +1.4mm Pattern correlations from 0.90 to 0.97 Knoche, 2005 from QIRCS project

12 Precipitation from RCMs Difference of annual means from observations BIAS from from -31 to +108 mm Pattern correlations from 0.48 to 0.90 Knoche, 2005 from QIRCS project

13 Projections for Europa year winter summer +10 C -1 C +50% (IPCC, 2007) -50% minus A1B-Scenario, 21 models Temperature increases, seasonal differences Precipitation: increase in the North, decrease in the South

14 Development of the CCLM 1996 first β-version of LM (Local Model) 1998 first official version of LM 1999 offical LM-version 1999 start of CCLM-development year simulation Climate Simulation start of Consortial Runs 2007 re-connection of LM and CCLM in COSMO 4.0 (from Rockel, GKSS, 2007)

15 COSMO/CCLM Community COSMO Community CCLM - Community From Rockel, GKSS, 2007

16 CCLM-Validation (Temperature) CCLM-CRU for Total year January July (from Will, BTU Cottbus, 2008)

17 CCLM-Validation(Precipitation) CCLM-GPCC for Total year January July (from Will, BTU Cottbus, 2008)

18 Consortial Runs (Setup)

19 Projections for Germany until 2100 with CCLM Modell preliminary Annual mean temperature Annual mean precipitation no trend trend: 2-3 C/100 years (K. Keuler, BTU Cottbus, 2007)

20 Projections for Germany until 2100 with CCLM Modell preliminary Number of days with T min < 0 C Number of days with precipitation > 10mm (K. Keuler, BTU Cottbus, 2007)

21 Projections for Germany until 2100 with CCLM Modell preliminary Number of days with snow Number of days with T > 25mm (K. Keuler, BTU Cottbus, 2007)

22 Observed Precipitation Trends Eastern Germany in % from Bernhofer et al., LandCaRe-Project, 2008

23 Comparison CCLM- Observations ( ) Temperature: CCLM too cold in Winter by about 0.5 C Precipitation: Regional differences of about 10% air temperature C precipitation % Bernhofer et al., LandCaRe-Project, 2008 Eastern Germany: Winter too cool Summer to moist

24 Trend over Germany vs A1B-Scenario Temperature: Warmer by about 1 C air temperature C precipitation % Precipitation: Increase in winter Decrease during rest of the year No winter incresae in Eastern Germany Bernhofer et al., LandCaRe-Project, 2008

25

26 Projected Trends in Snow

27

28

29

30 Projected Trends in Snow

31 Projected Trends in Snow

32 Projected Trends in Snow

33 Projected Trends in Snow

34 Projected Trends in Snow

35 Projected Trends in Snow

36 Conclusions (1) Many regional climate models (RCMs) with different development chains are available. RCMs need extensive validation before application in different regions. Usual RCM errors: Biases of about 2 C in temperature Biases of up to 50 % in precipitation (problems also in obserations Causes for errors/differences in RCM runs: Unresolved processes (e.g. convection) Choice of spatial resolution Uncertainty of boundary forcing Treatment of boundary forcing Choice of RCM domain Choice of emission scenario

37 Conclusions (2) Europe Winter: Drying in the south and moistening in the North Sommer: Drying everyhere, except Northwesterly regions Germany Regional differences, especially drying in the East in both summer and winter Decrease in snow cover in the low mountain ranges, no change in the alps

38 Outlook RCMs will go to higher resolutions in order to improve on physics RCMs and NWP models will continue to converge Common problem in for RCMs and NWP: Representation of physical processes in the models How to quantify the uncertainty in forecasts and projections How to generate and interprete ensembles