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Quantitative assessment of wind storms and extreme extratropical 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 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 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? UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 1. Introduction Potential Sources of Variability ~Decades AMM, PNA, AMO, ENSO ~Months SST, NAO, snow ~Days Growths factors for cyclones latent heat Cyclone & storm Baroclinicity Divergence Geopotential 500 hPa ~Centenial Anthropogenic Change Adapted fromLutgens & Tarbuck (Eds., 2007) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 ECMWF Forecast for 20.05.2010 00 UTC G.C. Leckebusch 2. Gaussian Perspective MSLP: Stormtrack NCEP-NCAR, 1961-2000 23 AOGCM Ensemble Ulbrich et al., 2008 J. Climate UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Gaussian Perspective 1000 hPa Stormtrack: ACC-Signal (SRES A1B) Ulbrich, Pinto, Kupfer, Leckebusch, Spangehl, Reyers (2008), J Climate UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks ERA40 Re-analysis: Track density Winter (ONDJFM), ALL Systems Ensemble Mean: Track density Winter (ONDJFM), ALL Systems 1961-2000 Unit: Systems per winter UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks A1B Climate Change Signal All Systems UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks Definition: Extreme Cyclone Systems Systems with a Laplacian of MSLP ( above the 95th 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) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks Weighting via: W A1B Climate Change Signal Strong Systems Weight: W2 Leckebusch et al., 2008b Weight: W4 For the region of e.g. NE Atlantic: ca. 10-20% increase UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks Cyclone Intensity (Laplacian of MSLP) for ALL Systems: UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 2. Lagrange Perspective: Cyclone Tracks European Storm Cyclones Change Signal GCM-Ensemble cyclone track density ERA40, 1961-2000 intensity of storm cyclones Max.Wind speed during storm days Isolines: Inter-model std.-dev UNESCO Extreme Meeting, Paris, 27.-29.9.2010 (Donat, Leckebusch et al., 2010a) G.C. Leckebusch 3. Wind storms: Identification Introduction of an objective Storm Severity Index (SSI) (cf. Leckebusch et al., 2008) vmax (k , t ) max 0, 1 Ak v98 (k ) k t K Ger T SSIT , KGer 3 Event Tracking: related to impacts 98th Percentile (ONDJFM) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 m/s G.C. Leckebusch 3. Wind storms: EVA • Generalized Pareto Distribution 1/ z G( z ) exp 1 d g ( z) G( z) dz 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) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 3. Wind storms: EVA NO All tracks are considered, which have at least one track point within the according region: NW NORTH-EUROPE (NO-EU) NORTH-WEST-EUROPE (NW-EU) SO SOUTH-EUROPE (SO-EU) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch Extreme value analysis: Ensemble composition and threshold Percentage of events from single model contribution to the ensemble Region: NW-EU % Threshold selection: On average 1 event per year and model: = 1024 storms SSI threshold: 11.19 SSI-Threshold UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 3. Wind storms: EVA Total numbers of events in each 30 year period Events: SSI > 11.19 ENSEMBLES Multi-model ensemble in A1B scenario Region: NW-EU Model composition for each 30 year period UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 3. Wind storms: EVA Return Level of a 50-year Event 1971-2000 EVA: stationary & non-stationary model UNESCO Extreme Meeting, Paris, 27.-29.9.2010 Region: NO-Europe 2069-2098 ENSEMBLES Multi-model ensemble in A1B scenario Region: NW-EU G.C. Leckebusch 3. Wind storms: EVA Relative changes of Return Levels by 2098 compared to 1971 Region RL5 RL10 RL25 RL50 RL100 NOEUROPE +53% +59% +67% +73% +79% NWEUROPE +13% +14% +15% +15% +16% SOEUROPE -19% -27% -36% -43% -49% Red: statistical significant on 95% level Trends (non-stationary model) UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 3. Wind storms: EVA ECHAM5-OM1: 3x30 Years of 20C climate conditions Germany !!! UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch 3. Wind storms: EVA Results based on 3 x 30 year simulation (ECHAM5-OM1) SRES A1B scenario Region: Germany 20112040 20412070 UNESCO Extreme Meeting, Paris, 27.-29.9.2010 20712100 G.C. Leckebusch 4. Summary 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 UNESCO Extreme Meeting, Paris, 27.-29.9.2010 G.C. Leckebusch