The impact of Nature-based Solutions (NbS) on hydrological processes in an agricultural catchment through their representation in a physically-based model

Traditional water management practices, largely based on hard engineered infrastructure and highly optimized systems, are proving insufficient for adapting to the complex interplay of future climatic, environmental and socio-economic conditions. The increased frequency and magnitude of hydrological hazards in Europe, such as the multi-year drought during the period 2018-2020 and the subsequent summer flood that hit Central Europe in July 2021, have underscored the need for integrated water management. Nature-based Solutions (NbS) offer a promising alternative or complement to grey infrastructure by leveraging natural processes and ecosystem services to simultaneously mitigate flood and drought risks. Unlike traditional water management, which has a well-developed knowledge base and specialized modelling tools to represent structural measures (e.g., dikes, dams) as well as guidelines to assess their performance, knowledge on NbS representation, functioning and their impacts on catchment hydrology over time is still limited. The simulation of NbS requires modellers to identify relevant hydrological processes involved in their functioning and find reliable ways to represent them based on the capabilities and limitations of selected physically-based models and available data. Agricultural catchments, while highly vulnerable to shifts in climate due to their dependence on natural climate-sensitive resources, offer significant opportunities for implementing nature-based strategies such as wetland restoration, tree planting and infiltration ponds. This study analyses the impact of NbS representation on the hydrological processes related to both floods and droughts in one middle-sized agricultural catchment under temperate climate: the Handzamevaart catchment (Belgium). Using MIKE SHE, a fully distributed hydrological model, coupled with MIKE 11, a 1D hydraulic river model, we explore a wide range of parameters to represent different types of NbS. Changes in the total water balance and in the individual hydrological processes and variables related to discharge, overland flow, evapotranspiration, infiltration, and groundwater fluxes obtained as a result of the different NbS representation will be assessed at catchment scale, but also locally - immediately upstream and downstream of the modelled measures. This study can serve to build the foundational knowledge required for the representation of NbS in physical models, anticipating process understanding for designing flood and drought mitigation strategies. Key outputs include an evaluation of model robustness to NbS representation, identification of the most influential parameters in the representation of different types of NbS, and thereby guidance for empirical data collection to improve NbS representation in future studies.

Research is supported by the Horizon Europe research and innovation programme: the “FUTURAL project” (Grant No. 101083958).