Leveraging soil diversity to mitigate hydrological extremes with nature-based solutions in productive catchments

Abstract. Nature-based solutions (NbS) are increasingly being explored as effective strategies for mitigating hydrological extremes, such as floods and agricultural droughts. Among these, soil-vegetation-based approaches may play a key role in improving soil health, enhancing ecosystem services, and restoring the natural hydrological cycle in productive agricultural and forestry catchments, making these landscapes more resilient to climate change. However, the influence of local factors, such as soil characteristics, on the effectiveness of these interventions is often overlooked. This study investigates the role of spatial variability of soil properties in shaping the effectiveness of NbS for mitigating both floods and agricultural droughts. To this end, two distributed, physically based hydrological models, one for an agricultural catchment and one for a forest dominated catchment, were developed, integrating two landscape planning scenarios involving a series of NbS to be represented. Key spatially based indicators to assess the effectiveness of NbS were developed based on long term simulation results. A major output from this study is that the effectiveness of NbS in improving flood and drought resilience is dependent on the soil’s natural drainage characteristics, with well-drained soils demonstrating the greatest potential. In well-drained soils, hedgerows significantly enhanced infiltration by improving soil hydraulic properties and creating additional air space in the soil's porosity through higher rates of evapotranspiration. In contrast, improving hydraulic properties in waterlogged soils had minimal impact on infiltration due to existing saturation, with anoxic conditions potentially limiting transpiration. Additionally, the study highlights that well-drained soils offer co-benefits for resilience to agricultural droughts, as they are more likely to experience water deficits that NbS can mitigate. In contrast, such benefits are generally absent in waterlogged soils, which rarely face water scarcity. Future approaches to evaluate the potential effectiveness of NbS should recognize the spatial variability in their performance. This variability should inform the type and location of NbS to increase their overall effectiveness.