Hourly model simulation to improve the estimation of extreme floods in small catchments in Western Germany

The July 2021 flood in Western Germany is one of the most severe flood events in small-scale catchments during the past decades. It has led to life loss and severe damage in the Ahr, Erft, and Rur basins. The BMBF-funded joint project KAHR (https://hochwasser-kahr.de) deals with the effects of this flood and develops scientific knowledge to assist the reconstruction process. To analyze past floods and develop future flood management strategies, there is a need for small-scale flood modeling with finer spatial-temporal resolution in this area. Based on the derived simulated floods, we can investigate the spatiotemporal patterns of extreme weather and associated meteorological and hydrological conditions that could lead to similar or more significant flood events.

This study uses the mesoscale hydrological model mHM at hourly resolution for three small catchments Ahr, Erft, and Rur. This is one of the first applications of mHM forced with hourly meteorological forcing data and should enable more accurate processes and representation of such extreme floods. In a further step, a regional weather generator and a disaggregation procedure are applied to generate 10,000 years of synthetic hourly meteorological data for the Ahr, Erft, and Rur catchments. These data are used to create long time series of discharge with the calibrated mHM model. This enables the investigation of extreme floods and the assessment of flood risk under future climate conditions.