1. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #1 Changes in storm occurrence over Northern-Central Europe

2. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #2 Summary The assessment of changing storminess is hindered by the inhomogeneity of wind-data, i.e., changes in wind statistics over the years do not necessarily (and, indeed: rarely) reflect changes in regional wind conditions, but are contaminated by various local and nonmeteorological factors, such as changing land-use, changing instrumentation and analysis practice. Instead, so-called proxies are employed to assess changing wind and storm statistics. Such proxies must represent storm statistics, and must not be affected by changes in the environment and in the observational practice. Unfortunately, economic damages can not serve for this purpose, but statistics about the frequency of low air pressure readings, strong spatial pressure gradients or deep short term pressure falls are useful proxies. They have been used in several studies for Northern Europe and Eastern Canada. An alternative is to derive storm indicators with regional climate models, which process homogeneously analyzed information about the large-scale circulation. Also this approach has successfully been used in the North Atlantic sector. In all cases, an intensification of storm activity was detected for the time of about 1970-1990; however, the trend has reversed since in both the proxy and the model studies; before the 1970s there was a long-term decrease in Northern Europe; in Eastern Canada there were equally phases of intensification and weakening, and no systematic change could be detected so far – which is –at least in Europe – consistent with model projections for the rest of this century. 30 minutes

3. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #3 Challenge Storminess best represented by wind statistics, possibly derived quantities such as stream function, vorticity, but wind time series are almost always inhomogeneous too short

4. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #4 Example of inhomogeneities in wind records

5. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #5 “Great Miami”, 1926, Florida, Alamaba – damages of 2005 usage - in 2005 money: 139 b$ Katrina, 2005: 81 b$ Pielke, Jr., R.A., Gratz, J., Landsea, C.W., Collins, D., Saunders, M., and Musulin, R., 2008. Normalized Hurricane Damages in the United States: 1900-2005. Natural Hazards Review The increase in damages related to extreme weather conditions is massive – but is it because the weather is getting worse? Losses from Atlantic Hurricanes Hardly

6. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #6 Wind, hydrology and outlook For assessing ongoing change of the occurrence of extremes as being (partly) not within the range of natural variations („detection“) and for attributing most probable causes to such changes („attribution“), we need homogeneous descriptions of past variability – for hundred and more years, and projections of possible futures. For planning suitable adaptation measures, such descriptions and projections need to be regional or local. For the case of wind-storms, methods have been developed – and likely, such methodology may be transferred to hydrological issues.

7. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #7 Two approaches: proxies + downscaling Challenge Storminess best represented by wind and precipitation short-term statistics but such time series are almost always inhomogeneous too short For assessing changing storm conditions, principally two approaches are possible: Use of proxies, such as daily and sub- daily air pressure readings. Empirical or dynamical downscaling of large scale information. Usage of weather analyses, incl. re- analyses and proxies such as damages are not suitable.

8. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #8 Two approaches: proxies + downscaling For assessing changing storm conditions, principally two approaches are possible: a)Use of proxies, such a air pressure readings. b)Empirical or dynamial downscaling of large scale information. c)Usage of weather analyses, incl. re- analyses and proxies such as damages are not suitable.

9. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #9 Pressure proxies

10. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #10 Pressure based proxies Air pressure readings are usually homogenous Annual/seasonal percentiles of geostrophic wind derived from triangles of pressure readings (e.g., 95 or 99%iles); such percentiles of geostrophic wind and of “real” wind are linearly related. Annual frequency of events with geostrophic wind equal or larger than 25 m/s Annual frequency of 24 hourly local pressure change of 16 hPa in a year Annual frequency of pressure readings less than 980 hPa in a year

11. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #11 Other storm proxies Variance of local water levels relative to annual mean (high tide) water level. Repair costs of dikes in historical times. Sailing times of ships on historical routes.

12. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #12 Proxies: N Europe

13. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #13 Geostropic wind stats N Europe Relevant publications 99%iles of annual geostrophic wind speeds for a series of station triangles in the North Sea regions and in the Baltic Sea region. Alexandersson et al., 2002

14. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #14 Local pressure stats since 1800 Relevant publications Time series of pressure-based storminess indices derived from pressure readings in Lund (blue) and Stockholm (red). From top to bottom: Annual number of pressure observations below 980 hPa (N p980 ), annual number of absolute pressure differences exceeding 16 hPa/12 h (N Dp/Dt ), Intra-annual 95-percentile and 99-percentile of the pressure differences (P 95 and P 99 ) in units of hPa. From Bärring and von Storch, 2005: see also BACC 2008. Stockholm Lund

15. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #15 Regional development of storminess and temperature Lund and Stockholm Unchanging extratropcial storm conditions is not contradicting the fact that temerpature is rising,

16. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #16 Proxies N + C Europe Matulla, C., W. Schöner, H. Alexandersson, H. von Storch, and X.L. Wang, 2007: European Storminess: Late 19th Century to Present, Climate Dynamics DOI 10.1007/s00382-007-0333-y

17. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #17 Proxies: Geostrophic stats 21 year Gaussian filtered normalized

18. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #18 24 hr pressure change stats normalized

19. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #19 Pressure Proxies E Canada Subarctic Arctic more less Change of intra-winter 10%-ile of pressure readings at E Canadian stations Halifax and Pondlnlet in the Arctic.

20. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #20 Applications: past and future marine weather in N Europe Globale development (NCEP) Dynamical Downscaling REMO or CLM Simulation with barotropic model of North Sea Cooperation with a variety of governmental agencies and with a number of private companies downscaling cascade for constructing variable regional and local marine weather statistics

21. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #21 Problem solved for synoptic systems in N Europe in CoastDat@GKSS, using RCM spectrally nudged to NCEP - retrospective analysis 1958-2005 - good skill with respect to statistics, but not all details are recovered. Weisse, R., H. von Storch and F. Feser, 2005: Northeast Atlantic and North Sea storminess as simulated by a regional climate model 1958-2001 and comparison with observations. J. Climate 18, 465- 479 Dynamical Downscaling: Baroclinic storms

22. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #22 Stormcount 1958-2001 Weisse et al., J. Climate, 2005 Change of # Bft 8/year t ≤ T t ≥ T

23. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #23 Continuous simulation with regional model CLM, 1948-2006, run and (large-scale) constrained with NCEP/NCAR re-analysis Dynamical Downscaling: Polar Lows

24. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #24 60 year simulation with 50 km grid, Experimental case and season simulations with embedded 18 km grid. Dynamical Downscaling: E Asian Typhoons

25. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #25 Note: different criteria employed

26. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #26 Conclusion: Usage of proxies 1.Monitoring extra-tropical storminess may be based on air pressure proxies. 2.This allows assessments for 100 and more years. 3.Decades long upward and downwards trends have been detected in recent years. 4.These trends are not sustained and have show recent reversals in all considered regions. 5.Recent trends are not beyond the range of natural variations, as given by the historical past, but are more of intermittent character. Regional temperatures rose significantly at the same time.

27. European conference for the insurance sector Insuring future climate change: Preparing and acting today, Oslo, November 3-4, 2008, #27 Conclusion: Usage of dynamical downscaling 1.Dynamical downscaling for describing synoptic and mesoscale variability is doable. 2.Spectral nudging, or other forms of large-scale constraint are helpful. 3.Simulation of extra-tropical baroclinic disturbances satisfying; wind my be used for simulating wave and surge climatologies and trends. 4.Meso-scale variability (Polar Lows and Tropical Cyclones) is also described, but the depth of the cyclones is not as deep as found in reality; also the winds are too weak. 5.Validation difficult, because homogeneous long term observed data do hardly exist. 6.Analysis of 60 year simulations point to strong year-to-year variability, to less decade-to-decade variability and no noteworthy trend.