Abstract
Abstract. The extent and location of impervious surfaces within urban areas due to past and present city development strongly affects the amount and velocity of run-off during high-intensity rainfall and consequently influences the exposure of cities towards flooding. The frequency and intensity of extreme rainfall are expected to increase in many places due to climate change and thus further exacerbate the risk of pluvial flooding. This paper presents a combined hydrological-hydrodynamic modelling and remote sensing approach suitable for examining the susceptibility of European cities to pluvial flooding owing to recent changes in urban land cover, under present and future climatic conditions. Estimated changes in impervious urban surfaces based on Landsat satellite imagery covering the period 1984–2014 are combined with regionally downscaled estimates of current and expected future rainfall extremes to enable 2-D overland flow simulations and flood hazard assessments. The methodology is evaluated for the Danish city of Odense. Results suggest that the past 30 years of urban development alone has increased the city's exposure to pluvial flooding by 6% for 10-year rainfall up to 26% for 100-year rainfall. Corresponding estimates for RCP4.5 and RCP8.5 climate change scenarios (2071–2100) are in the order of 40 and 100%, indicating that land cover changes within cities can play a central role for the cities' exposure to flooding and conversely also for their adaptation to a changed climate.
Highlights
The intensified urbanisation caused by rapid population growth and increasing rural migration is in many studies found to be a major cause of amplified peak flows and increased flood risk in cities worldwide (Chang and Franczyk, 2008)
An urban land cover change analysis for Odense based on remote sensing estimates shows an overall increase in absolute imperviousness of 19 %, from 32 % in 1984 to 51 % in 2014 (Fig. 2c)
Results are shown only for those parts of the city which are currently connected to the urban drainage system, which comprises the majority of the urban area
Summary
The intensified urbanisation caused by rapid population growth and increasing rural migration is in many studies found to be a major cause of amplified peak flows and increased flood risk in cities worldwide (Chang and Franczyk, 2008). Changes in the urban land cover are important factors for the increased susceptibility to flooding. Climate change is expected to exacerbate the flood risk as heavy precipitation is projected to increase in intensity and frequency over many areas of the globe, including central, northwest and northern Europe (Field et al, 2012; EU and EEA, 2012). Most major cities in Europe are characterized by IS fractions ranging from 50–75 % or even higher (EU and EEA, 2012). If present trends towards increasing IS fractions continues this is expected to further aggravate the risk of pluvial flooding.
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