Investigating the effectiveness of Nature-Based Solutions (NBS) for climate change adaptation: The case study of Aa of Weerijs catchment, The Netherlands.

Anthropogenic Climate Change has caused an increase in frequency, intensity and impact of hydro-meteorological-hazards (HMHs) such as floods, droughts, wildfires, and sea level rise. Prior to the 21st century, most policies and strategies to deal with water-related climate risks were based on conventional or grey solutions without considering Nature-Based Solutions (NBS) as potential measures. In the recent past, NBS has gained prominence over conventional measures, in the long run, owing to multi-functionality, flexibility, and cost-effectiveness, providing inter-related and multi-scale benefits to deal with water-related climate hazards.

However, the efficiency and robustness of NBS are still under question because of the lack of specialized models and tools to assess them throughout the life cycle and under varying climate patterns. A solid framework of Key Performance Indicators is needed to progress further in promoting NBS at larger scales.

In this study, we have explored a set of potential NBS for the Aa of Weerijs catchment, in the Netherlands, which is currently under water stress. The performance of NBS to deal with water-stress-related challenges in the catchment is investigated using a fully distributed physical coupled MIKE SHE-MIKE11 model previously developed. A different set of scales and extents and combinations of NBS have been modelled in the MIKE SHE model of the catchment, ranging from wetlands, detention ponds and river meandering. The performance of NBS is evaluated both for the present and for future climate change conditions, using two sets of climate change projections, the KNMI ’14 scenarios, developed by the Koninklijk Nederlands Meteorologisch Instituut (KNMI), and the RCP 6.0 and RCP 8.5 scenarios, provided by Copernicus.

To assess the performance of each NBS set-up and support informed decision-making for stakeholders, a suite of defined KPIs, including surface and groundwater availability in the catchment, water stress ratio, and soil moisture deficit index, is being calculated for each NBS simulation run and used for comparison with base results.

The study results are intended to support NBS impact evaluation as an adaptation strategy for the long term.