Development of a high-resolution model system for assessing an urban flood event in past and future climate

On May 10^th, 2018, Lohbrügge, a city quarter in the eastern part of Hamburg, Germany, was hit by a local heavy rainfall event. Within a short time, the sewer system was overloaded and parts of Lohbrügge were flooded. Meanwhile, city quarters around Lohbrügge had a warm and sunny early summer day.

One aim of the project CLICCS-C1 is the high-resolution simulation of the “Lohbrügge event” with a coupled model system including an atmospheric and a hydrological/hydrodynamical model. For a realistic representation of the meteorological situation and the rain amount, the microscale obstacle-resolving model of the atmosphere MITRAS is forced with two different types of radar data and one set of analysis data from COSMO-D2 model. In a sensitivity study, the results of the three MITRAS simulations as well as the different radar data itself are used for offline coupling the hydrological/hydrodynamical model KALYPSO. The water levels and water flow rate are qualitatively compared with available documentation of the flooding, e. g. photos. Due to the limited extent of the event, no surface based meteorological measurements are available.

In order to investigate the magnitude of such an event in a future climate, the past event is transferred into a future heavy rainfall event for the area of Lohbrügge. The model system shall than be used for assessing the impact of adaptation measures such as green infrastructures for water retention and flood reducing. The impact of adaptation measures shall be evaluated for the past and future climate heavy rainfall event.

In this contribution, results of the sensitivity study of the coupled model system will be presented. How to design a climate future heavy rainfall event for a high-resolution coupled model system will be outlined.