Exploring spatial effectiveness of NBS measures for flood mitigation with OpenLISEM

Nature based solutions (NBS) are often considered as one of the potential measures to improve the flood resilience of landscapes. In the Geul catchment, located in eastern Belgium and the south of the Netherlands, the severe flooding event of summer 2021 significantly increased attention on the potential for NBS. Although many stakeholders and institutes see potential value of implementing NBS in the catchment, many uncertainties about their effectiveness hamper fast action and decision making. Applying a spatially distributed model to explore the potential of NBS on local and regional scales, can provide valuable answers to the question of which NBS, and in which spatial configuration can minimize flood risk. Within the LandEX project, funded by Water4All, the aim is to study how the spatial distribution of NBS can improve the resilience of landscapes against hydroclimatic extremes. One of the case study areas in this project is the Geul catchment. We applied the OpenLISEM model to multiple sub catchments of the Geul river to quantify the effectiveness of multiple NBS for flood risk reduction, which were selected based on a participatory workshop. The study investigates how the catchment characteristics like land use, slope steepness and management, as well as the spatial placement and configuration of NBS influence the effectiveness to reduce flood risks. A secondary result of this study is the further exploration of approaches to parametrize NBS in a process-based model. The results of this application of OpenLISEM can be used to further understand the processes influenced by NBS and how to include these in modelling and scenario analyses. In addition, local stakeholders and decision makers can use the modelling results as a basis for the spatial implementation of NBS.