Learning from the past to inform flood risk management: Analysis of public survey data in Belgium on flood early warning and response during the July 2021 flood

In July 2021 an intense and rapid onset rainfall event resulted in severe flooding in Belgium as well as neighbouring countries of Germany, the Netherlands, and Luxembourg. The region of Wallonia in Belgium was severely affected with the Vesdre River valley in the province of Liège being particularly hard-hit, with 39 reported fatalities there. The warning system was significantly criticised in the aftermath of the event. Hence, this work addresses the flood forecasting warning and response system (FFWRS) performance in Belgium for the July 2021 flood with a focus on Wallonia. The analysis is based on an online survey (n=550) and addresses the reception of official warnings, interpretation and trust in the warnings, and response behaviour. We investigate which variables may influence behaviour and situational factors which leads to people receiving an official warning in time before the flood including flood severity experienced and risk perception. We find that among the respondents in Wallonia 33% reported that they had not been warned and while 28% were warned through official channels, many did not know how to respond. From a similar survey conducted in Germany we see comparable results, suggesting that there were similar cross border challenges. A first regression analysis of the Belgian data suggests that respondents whose household was highly affected were less likely to receive an official warning in time which is consistent with testimonies reporting that inhabitants in severely affected areas were particularly surprised by the flood. We also investigate the role of risk perception and flood warning. This points to some of the challenges with effectively early warning for flash floods. Our analysis highlights the need to improve Belgium's flood warning system by ensuring timely issuance of warnings and enhanced public understanding. In addition, with a comparison of results to the Germany data we discuss common challenges but also important differences.