Seeking Flood Risk-Minimization: How to Benefit from the Use/Availability of Heavy Rainfall-Risk Maps

Abstract

The 2021 flooding events in The Netherlands, Belgium and Germany have sensitized many municipalities across Europe and especially in Germany, the federal states of North Rhine-Westphalia (NRW) and Rhineland-Palatinate, having been particularly affected, have formulated more extensive requirements for the municipalities to be able to manage these drastic situations. Flood risks and heavy rainfall maps are crucial instruments in this context because they serve as a basis for identifying risks and also for selecting suitable measures to minimize them and, in 2021, in Germany, the Federal Agency for Cartography and Geodesy (BKG) made available for the first time a state-wide, cross-municipal heavy rainfall information map for the state of North Rhine-Westphalia, in which heavy rainfall and flooding risks are recognizable for every citizen. Therefore, municipalities that already had their own heavy rainfall maps had a comparative possibility of plausibility checks, while those that did not yet have their own heavy rainfall map, had the possibility to benefit from these resources. Especially in this second scenario, the municipalities and the wastewater utilities need reliable practical advice on how to classify the information from the maps regarding drainage consequences, and this paper aims to fill this void, summarizing the experience of the 80 municipalities represented in the KomNetAbwasser in dealing with heavy rainfall maps and discussing requirements for their informative value. Furthermore, measures for risk minimization and their prioritization are also proposed, focusing on risk identification, organizational tasks, action planning and implementation, analysis of the hazard maps, risk assessment and the selection of emergency measures.