1. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Quantitative assessment of wind storms and extreme extra- tropical cyclones under climate change Gregor C. Leckebusch Special Thanks to: M. Donat, D. Renggli, T. Kruschke, K. Nissen, P. Lorenz, T. Pardowitz, U. Ulbrich Institute of Meteorology Freie Universität Berlin, Germany

2. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 0) Outline Introduction to extra-tropical cyclones Gaussian and Lagrange Perspective of Cyclonic Activity Recent climate conditions Anthropogenic Climate Change Objective Wind Storm Identification Extreme Value Analysis Anthropogenic Climate Change Summary

3. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 1.Introduction Extra-tropical Cyclones: Crucial part of atmospheric circulation; Highly relevant for energy transports Objective Measure of its strengths? How to deduce information about potential changes of these extreme events? Which processes influence the variability of cyclone occurrence?

4. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Cyclone & storm ~Months ~Days SST, NAO, snow Growths factors for cyclones latent heat Divergence Baroclinicity Adapted fromLutgens & Tarbuck (Eds., 2007) ECMWF Forecast for 20.05.2010 00 UTC Geopotential 500 hPa Potential Sources of Variability ~Decades AMM, PNA, AMO, ENSO ~ Centenial Anthropogenic Change 1.Introduction

5. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch MSLP: Stormtrack Ulbrich et al., 2008 J. Climate 2. Gaussian Perspective NCEP-NCAR, 1961-2000 23 AOGCM Ensemble

6. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Ulbrich, Pinto, Kupfer, Leckebusch, Spangehl, Reyers (2008), J Climate 1000 hPa Stormtrack: ACC-Signal (SRES A1B) 2. Gaussian Perspective

7. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch ERA40 Re-analysis: Track density Winter (ONDJFM), ALL Systems Ensemble Mean: Track density Winter (ONDJFM), ALL Systems Unit: Systems per winter 1961-2000 2. Lagrange Perspective: Cyclone Tracks

8. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch A1B Climate Change Signal All Systems 2. Lagrange Perspective: Cyclone Tracks

9. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Definition: Extreme Cyclone Systems Systems with a Laplacian of MSLP ( ) above the 95 th percentile, i.e. only the upper 5% of the distribution are recognised here NCEP or ERA40 re-analysis: most of the historical relevant winter storms are included (as far as storms are resolved by re-analysis data) 2. Lagrange Perspective: Cyclone Tracks

10. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch A1B Climate Change Signal Strong Systems Weighting via: W Weight: W 2 Weight: W 4 For the region of e.g. NE Atlantic: ca. 10-20% increase 2. Lagrange Perspective: Cyclone Tracks Leckebusch et al., 2008b

11. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Cyclone Intensity (Laplacian of MSLP) for ALL Systems: 2. Lagrange Perspective: Cyclone Tracks

12. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch European Storm Cyclones ERA40, 1961-2000 Change Signal GCM-Ensemble cyclone track density intensity of storm cyclones Max.Wind speed during storm days (Donat, Leckebusch et al., 2010a) Isolines: Inter-model std.-dev 2. Lagrange Perspective: Cyclone Tracks

13. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Introduction of an objective Storm Severity Index (SSI) (cf. Leckebusch et al., 2008) 98th Percentile (ONDJFM) m/s Event Tracking: related to impacts 3. Wind storms: Identification

14. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Generalized Pareto Distribution ξ : shape σ : scale μ : shift Probability density function (pdf) Containing 3 families of tail distributions Rotated Weibull (with upper bound)ξ < 0 Gumbel (no bound, exponential decay of pdf) ξ = 0 Fréchet (no upper bound, polynomial decay of pdf)ξ > 0 e.g. Coles, An Introduction to Statistical Modeling of Extreme Values (2001) 3. Wind storms:3. Wind storms: EVA

15. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch All tracks are considered, which have at least one track point within the according region: NORTH-EUROPE (NO-EU) NORTH-WEST-EUROPE (NW-EU) SOUTH-EUROPE (SO-EU) NO NW SO 3. Wind storms: EVA

16. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Threshold selection: On average 1 event per year and model: = 1024 storms  SSI threshold: 11.19 Percentage of events from single model contribution to the ensemble Extreme value analysis: Ensemble composition and threshold % SSI-Threshold Region: NW-EU

17. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Total numbers of events in each 30 year period ENSEMBLES Multi-model ensemble in A1B scenario Region: NW-EU Model composition for each 30 year period Events: SSI > 11.19 3. Wind storms: EVA

18. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2069-2098 1971-2000 Return Level of a 50-year Event Region: NO-Europe EVA: stationary & non-stationary model ENSEMBLES Multi-model ensemble in A1B scenario Region: NW-EU 3. Wind storms: EVA

19. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch RegionRL5RL10RL25RL50RL100 NO- EUROPE +53%+59%+67%+73%+79% NW- EUROPE +13%+14%+15% +16% SO- EUROPE -19%-27%-36%-43%-49% Relative changes of Return Levels by 2098 compared to 1971 Trends (non-stationary model) Red: statistical significant on 95% level 3. Wind storms: EVA

20. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch ECHAM5-OM1: 3x30 Years of 20C climate conditions Germany !!! 3. Wind storms: EVA

21. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2011- 2040 2041- 2070 2071- 2100 Results based on 3 x 30 year simulation (ECHAM5-OM1) SRES A1B scenario Region: Germany 3. Wind storms: EVA

22. UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Different methods to assess the potential anthropogenic changes in synoptic cyclone behaviour were applied or newly developed Stormtrack: A 23 MME reveals significant increase at the downstream end of the climatological storm track over the North-Atlantic under ACC conditions Cyclone tracks: ACC: Reduction in the number of all cyclones on an hemispheric scale Increase in frequency of severe cyclones in winter in certain “hotspots”, e.g. Northeast-Atlantic Extreme Value Analysis identifies changes in the statistical properties of the frequency of severe wind storms 4. Summary