RIM2D – fast 2D hydraulic modelling for operational flood and flood impact forecast

The disastrous floods of July 2021 in Germany has shown, that abstract forecasts of river discharge or water levels at selected gauges do not provide sufficient information for timely and location specific warning of the population and targeted disaster management actions. The forecasts as well as the available flood hazard maps did neither allow for detailed information, which areas will actually be affected, nor could any information about the severity of the flooding derived. In order to provide better informed flood forecasts, RIM2D was developed. It solves the inertial formulation of the shallow water equations on a regular grid, and is highly parallelized on Graphical Processors (GPUs). Moreover, the modelling concept is parsimonious and allows for fast model setup. We will show that hydraulic simulations driven by the available gauge forecasts would have been feasible with sufficient lead time to provide spatially explicit forecasts of inundation depths and flow velocities. Moreover, we also show that impact forecast derived from the simulations would in terms of hazard maps indicating human instability in water and building failure hazard can be additionally derived for the operational forecasts. We argue that using these hydraulic and impact forecasts would have had an substantial impact on the flood alertness of the population and responsible authorities, enabling a better early warning and disaster management, which eventually saves lifes in such extreme flash flood conditions.