A climate modelling analysis of the Plan-B region in Vorarlberg, Austria

In order to plan and implement appropriate adaptation measures to protect settlements, the economy and other assets from natural hazards, it is important to know the potential consequences of climate change. Accordingly, the Plan-B model region within the Rhine Valley of the west-Austrian state of Vorarlberg is supported by the KLAR! program of the Austria Climate and Energy Fund to assist with this endeavour. The region encompasses some 91,000 inhabitants, making it one of the most densely populated regions in Austria. 

The focus of this work was on a detailed climate modelling study of the Plan-B region using the microscale urban climate model MUKLIMO_3. An accurate representation within the model involved processing input data from the Copernicus high-resolution datasets such as the digital elevation model, CORINE land cover, imperviousness and tree cover density supplemented by locally available building, land cover and vegetation data. The availability of measurements from a dense network of weather stations during July 2022 allowed the model accuracy to be evaluated for two case studies, and showed good results in representing the spatial variations of the region at a resolution of 50 m.

The modelling results from MUKLIMO_3 for the historical and current climate periods show hot-spots concentrated within the built-up urban areas. In such locations, annual averages of up to 70 summer days and 27 hot days are simulated for the period 1991-2020, consistent with the observations. Conversely, in the vicinity of water bodies such as Lake Constance, within parks or areas outside the urban fabric, annual averages of about 20-30 summer days and 2-8 hot days are more typical. From 1961 to 2020 the annual numbers of summer days, hot days and tropical nights are shown to increase across the entire domain reflecting the warming trend due to climate change. 

Climate model projection data from an ensemble of EURO-CORDEX models under the emissions scenarios RCP4.5 and RCP8.5 are input to show the expected heat load changes across the region for two future time periods. When compared with the 1991-2020 period, 2041-2070 can expect local increases of up to 20 summer days and 4 hot days for RCP4.5, and 28 summer days and 9 hot days for RCP8.5. A larger disparity in the results between the scenarios is shown for the period 2071-2100, with local increases of up to 56 summer days and 35 hot days for the extreme RCP8.5 scenario simulated relative to the 1991-2020 period. These results provide important information for decision makers and urban planners on where climate change adaptation measures to reduce heat load should be planned.