RainAhead – Integrated Planning and Warning Tool for Heavy Floods in Urban Areas | Umweltbundesamt

Climate scenarios:
For the project RainAhead results and data from the project "Design of road drainage facilities according to RAS-Ew and RiStWag against the background of changed temperature and precipitation events caused by climate change in Germany until the year 2100" of the Federal Highway Research Institute could be used. Detailed evaluations were carried out for the heavy rain risk for four study areas in Germany, of which one (large area of the motorway A1 Hamburg - Puttgarden) also includes the urban area Lübeck. The basis is formed by the CLM runs CLM-C20_1,2 and CLM-A1B_1,2 for the reference period 1961-1990, as well as for the periods 2021-2050 and 2071-2100. The runs use drive data from the global model ECHAM5-MPIOM with the SRES emission scenario A1B and were calculated with a grid spacing of 0.165 ° (~ 18 km) 17. Based on daily CLM data on temperature and rainfall, a bias correction of daily rainfall totals and a statistical downscaling was performed to derive information on high temporal and spatial high-altitude precipitation.

Measurements from the DWD since 1950 have been used: station data from rain station stations (temporal resolution 5 min), climate stations (daily values temperature and precipitation) and REGNIE data (daily precipitation totals, interpolated on a 1x1 km grid from 1951-2010, DWD, 2011). According to continuing Rainfall data it was examined how the projected changes affect the local heavy rain statistics on average. As a result of this evaluation, the number and intensity of heavy rainfall events increase. Thereafter, it is statistically significant to expect rainfall intensity in an extreme heavy rain event (with a duration of
15 min to 1 h and a statistical recurrence period of 5 years) in the period 2071-2100 is about 20% higher than in the reference period. The results of the station time series and the heavy rain trends until 2100 were compared with design rain. These are very high for the Lubeck region, which can be explained by the fact that there were fewer and shorter test series compared to today and the evaluations were accordingly less robust. Since the centennial design rain is even higher than the 2100 scenario and also represents a size used in practice, it was used to model the pilot areas in work package 3.

1961-1990

To simulate heavy rainfall, coupled, hydrodynamic 1D sewer network and 2D surface models were simulated. Bases for small-scale climate projections come from databases from EU projects PRUDENCE and ENSEMBLEs.

The risk assessment covered various aspects of urban infrastructure and can be extended for other data sets and issues. The maps of sinks and flow paths from the GIS flow path analysis, as well as the maps of flood levels from the 1D-2D modeling, in and of themselves, provide valuable information for planners, municipalities and the population. They also flowed into the risk maps as input variables and will continue to be used in the city administration, as well as the measures proposed in the model for improving the drainage situation in existing buildings.

Basic data included the topography and infrastructure, as well as uses and sensitive natural assets against flooding, objects with potential hazards.

Within the framework of a sensitivity analysis in the area of dangers / sensitivities of the city infrastructure, a GIS-supported risk assessment was undertaken. Factors such as the administrative structure or network of the participants played a role.

Essentially, already existing data should be used, so another criterion for the inclusion of input data in the sensitivity analysis was their presence in spatial form. Various communal data were requested, prioritized and reduced: this resulted in the four data segments population, sources of danger, protected goods / infrastructure and environmental and soil data. Based on DWA-M 119, these were assigned damage potentials.

Furthermore, potential damage scores have been defined for selected objects, e.g. Mixing water shafts, fuel oil tanks, swimming pools, rainwater retention basins and geothermal probes. Some of the data - especially those from the Environmental Data segment - was not assigned a rating due to an ambiguous relationship to the heavy rain event. These are very helpful for other investigations, such as the urban climate.

To assess the risk of flooding, a GIS-based estimation of the sinks and main flow paths of the surface water was carried out in the entire Lubeck urban area. In addition to the GIS software ArcMap, the free extension ArcHydro (ESRI) was used. The basis for creating the sink and flow path maps was a digital terrain model with a resolution of 1x1 m, created on the basis of a laser scan data set from 2006.

Another risk analysis took place. In order to identify and present the risk of heavy rainfall related damage, the risk of flooding from the GIS analysis or 1D 2D model and the potential damage (sensitivity analysis) were combined. There were based on the flood risk map in accordance with HWRM-RL 2007/60 / EG, but chose a modular representation for different object categories in order to create a basis for the sensitization of target groups.

Using the example of two pilot areas, the flood risk potential was specified. The topographical conditions were cleaned up and subsequently simulated and flooded.

On basis of the calculated flooding hazards in the urban area, a classification and risk assessment based on the depth and, for the fire brigade, in addition to the volume was determined in accordance with DWA-M 119,. The depths and volumes classified sinks served as input for the risk assessment.

Following the analyses, model measures were implemented and subsequently evaluated. The simulated measures were transferred to a plan which shows measures. It is possible to derive long-term planning principles that make the drainage system more robust, as well as short-term protection measures for flood events in the current state.