Hungary - Urban Pluvial Flooding Hazard Maps for Budapest - DTU

The data comprises of five flood hazard maps for Budapest and the surrounding area. The data shows the impacts of urban flooding (maximum inundation depth) as a result of high-intensity precipitation corresponding to 2, 10, 20, 50 and 100-year return periods under present-date climatic conditions.

The simulation is based on a digital elevation model (DEM) with a spatial resolution of 25 x 25 meters. The Danube river is “burned” into the DEM by adding a border around it. This is done in order to replicate the actual conditions, where surface runoff in the inner city, due to the city’s flood defenses, is prevented from draining directly into the river. Hence drainage to the river can only occur via the urban drainage system. Outside of the city center this may not be so however this is not currently included in the model. The extent of impervious surfaces (IS) is very influential on the runoff in cities. The present analysis of IS for Budapest has been inspired by Kaspersen et al. (2015), where a regression modelling approach has been applied in order to convert Soil Adjusted Vegetation Index (SAVI) values to IS fractions.

The presence of an urban drainage system is simulated by adding a conceptual drainage capacity, which is constant in time and varying in space. The drainage depends on the degree of IS, and is fully effective when the degree of IS is 100%. The drainage capacity is calibrated to a 2-year return period precipitation event, which resulted in an estimated value of 1000 mm/day. This corresponds approx. to 115.7 l/s·ha. The infiltration from non-impervious areas is based on soil characteristics for the Budapest area and the terrain slope and is everywhere set to 134 mm/day, which is a low value expected to correspond mainly to the conditions in the city center. Outside of the city, in more rural areas, the expected infiltration capacity could potentially be higher. The infiltration depends on IS, and is most effective where the degree of IS is 0%.

Skougaard Kaspersen, P., Høegh Ravn, N., Arnbjerg-Nielsen, K., Madsen, H., Drews, M., 2017. Comparison of the impacts of urban development and climate change in exposing European cities to pluvial flooding. Hydrol. Earth Syst. Sci. Discuss. 1–26. doi:10.5194/hess-2017-242.