Assessing the effectiveness of green and grey solutions for flood risk reduction: a comparison of damage-based and score-based approaches

Nature-based solutions are increasingly recognized as a critical component of adaptation of our society to extreme hydro-meteorological events. Reliable tools for assessing the effectiveness of such measures, particularly in comparison with grey solutions, are instrumental to ensure sustainable flood risk management under climate evolution and rapid urbanization. This study compares a monetary damage model and a scorebased approach to estimate the benefits of the implementation of green, grey, and hybrid measures for reducing flood risk. A representative case study was selected in the Vesdre catchment (Belgium), which was severely affected by the mega flood of 2021 in Europe. The research aims to assess the compatibility and complementarity of the two assessment approaches for evaluating the effectiveness of green solutions compared to traditional grey measures, emphasizing the added value of hybrid approaches. By addressing a key gap in flood risk evaluation frameworks, this work contributes to understanding how combined strategies can improve resilience and mitigate flood impacts in vulnerable regions.