Mapping of radar-based heavy rainfall risk in Germany for assessing the impact of extreme precipitation events

In a currently changing climate the frequency of extreme rainfall events in Central Europe is expected to alter, even despite dry episodes will be more common. Heavy rainfall with its dynamic and sometimes unpredictable character can provoke numerous hazards, like flash-floods, landslides and soil erosion, causing damages and huge economic costs, as well as direct threat to human life. Thus, it is important to not only monitor current rainfall events and warn against their occurrence, but also to understand the possible impact each event may provoke and provide communities with information on risked areas.

The aim of this study is to evaluate an overall heavy rainfall risk for the area of Germany. Following the IPCC definition of risk, we consider its three main determinants: hazard, exposure and vulnerability.

At first, two radar-based datasets have been used to map overall heavy rain hazard: the high-resolution radar climatology RADKLIM and the Catalogue of Radar-based Heavy Rainfall Events (CatRaRE), both developed by the Deutscher Wetterdienst (DWD) and currently available for the last 22 years (2001-2022). Frequency and hot-spots of past heavy rainfall events have been investigated e.g. based on their return period, extremity or area.

In order to determine the exposure, imperviousness degree and topographic position index (TPI) are combined together. For the monitoring of current risk, data on antecedent precipitation and soil moisture are additionally incorporated. Finally, potential vulnerability has been estimated on the basis of socioeconomic factors and past losses.

In addition, by combining the meteorological and non-meteorological variables of all past CatRaRE events together with data on insurance losses or fire-brigades’ operations, the impact of analogue upcoming events could be defined.

We will present the first results of a heavy rainfall risk mapping for the area of Germany, including all three risks components: hazard, exposure and vulnerability. We will also give examples of using the risk map as a basis for assessing the impact of operationally detected and/or predicted precipitation events.