IC2_I Scenarios of future changes in the occurrence of extreme storm surges Nilima Natoo A. Paul, M. Schulz (University of Bremen) M. Hadfield (University of Waikato) Motivation and Research Questions Changes in the planetary wind system under ongoing global climate change (IPCC, 2007) would have serious socio-economic implications, especially in coastal and low-lying regions. Storm events are closely related to extreme winds and precipitation, therefore any change in their position and intensity would directly influence the weather and climate of these regions (Brayshaw, 2009). Numerical climate models are considered as one of best tools to assess possible future changes in storminess in coastal areas. The North Sea and New Zealand regions both have a history of strong mid-latitude storms with large socio-economic effects. This research aims to answer the following questions: (1) Are any significant changes in mean storminess to be expected by the end of the 21 st century? (2) Does regional atmosphere-ocean coupling help to improve the predictability of mean storminess during the 21 st century? Universität Bremen THE UNIVERSITY OF WAIKATO Methodology ROMS: Regional Ocean Modeling System WRF: Weather Research and Forecasting model COAWST: Coupled Ocean- Atmosphere-Wave-Sediment Transport Modeling System Discussion and Outlook ROMS stand-alone model runs will be continued as planned (Figure 1). IPSL_CM5A_LR model results will be used as forcing and boundary data for WRF stand-alone and coupled model runs. A first comparison of monthly averaged results of hisr1 and rcpr1 shows a mean increase in sea- surface temperature by ~4 °C. However, for conclusive results, the runs need to be completed and the 2 nd and 3 rd ensemble member need to be added. B. Feasibility test: coupled WRF-ROMS (using reanalysis data) Figure 3 Exchange of data fields during coupling between atmosphere (WRF) and ocean (ROMS) components of the COAWST modeling system Model set-up: horizontal resolution 0.25° (~25 km); time steps: WRF 90 s, ROMS 180 s; coupling interval 180 s Forcing and boundary conditions: WRF model: 6-hourly NCEP Final Analyses data; ROMS model: 3-hourly IPSL_CM5A_LR global model results Coupled WRF-ROMS model WRF humidity (%), temperature (°C), height (m) at 850 hPa ROMS sea surface temperature MCT Coupler SST Uwind, Vwind, RH, Tair, Pair, cloud, rain, swrad, lwrad Results A. ROMS stand-alone model run Model Set-up: horizontal resolution 0.25° (~25 km), vertical resolution 32 layers; time step: 180 s Physics options: surface forcing calculated from bulk formulas; Mellor-Yamada 2.5 scheme for vertical mixing Boundary conditions and forcing data: IPSL_LR_CM5A global model results of Historical (hisr1) and Representative Concentration Pathways (RCP) 8.5 W/m 2 (rcpr1) experiments with ensemble member r1i1p1 Figure 1 Methodology Figure 4 Sea level pressure field as an indicator of weather (high: calm, low: storms near the earth’s surface), snapshot at from coupled test run Sea Level Pressure contour (hPa) Surface air temperature (°C) Sea Level Pressure Contours: 900 to 1100 by 4 °C Figure 2 Comparison of monthly averaged results of ocean surface fields (sea-surface temperature, air pressure and wind speed) from historical (January 1960) and RCP8.5 (January 2095) runs Historical run (hisr1) RCP8.5 scenario run (rcpr1) Latitude, degrees Longitude, degrees Latitude, degrees Longitude, degrees Latitude, degrees Longitude, degrees Latitude, degrees Longitude, degrees Latitude, degrees Longitude, degrees Latitude, degrees Longitude, degrees