Urban flooding — impervious surfaces reduce the drainage of rain water and increase the risk for urban flooding

Methodology

The degree of soil sealing is taken from the Pan-European soil sealing layer that contains the degree of soil sealing. To approximate the morphological area of the city, the reference unit is composed of the Urban Morphological Zones (derived from CLC 2006) inside the core city boundaries (core city defined in Urban Atlas / Urban Audit) and above a threshold of 10ha. Those reference unit objects have been overlaid onto the soil sealing mosaic of Europe to compute the mean soil sealing degree of each core city-UMZ by means of zonal statistics. Those values have again been classified into four classes and presented as coloured dots.

The modelled map has been computed in the framework of the ESPON Climate project and shows the change in annual mean number of days with extreme precipitation (>20mm/day) between the CCLM scenarios run (2071-2100) and the reference run (1961-1990) for IPCC scenario A1B. Those data are calculated based on the CCLM parameter ‘rainfall’ (yearly). This indicator will illustrate regional exposure to changes in heavy rainfall events and thus indicate hydrologic extremes. This variable has strong relevance for local heavy rainfall event, especially when occurring over highly sealed surface area