Assessing the effectiveness of Nature-based Solution as a climate change adaptation strategy using a coupled hydrology-soil erosion-river morphodynamics model

Nature-based Solutions (NBS) are potentially cost-effective adaptation strategies to combat the projected negative impact of climate change on water security and encompass a broad range of actions that protect, restore, or sustainably manage ecosystems to provide benefits to society. It is crucial to assess the effectiveness of NBS at the catchment scale, which is most relevant for policymakers. Here we present a new channel module for the hydrology-soil erosion model SPHY, with the aim to support the evaluation of multiple NBS in large-scale catchments. The model SPHY simulates all relevant hydrological and soil erosion processes, including infiltration excess surface runoff and soil detachment by raindrop impact and runoff. We developed a novel channel module that simulates river hydraulics and morphodynamics in the channel network. The channel module allows to simulate a wide variety of NBS. For instance, stream restoration practices can be simulated by changing the channel dimensions and floodplain cover. Vegetated buffer strips can be implemented by changing the vegetation cover on the hillslopes. To test its applicability for simulating NBS, we applied the model in a small Mediterranean catchment in southeast Spain, which is characterized by an increase of extreme precipitation under climate change. We simulated three types of NBS, i.e. (1) vegetated buffer strips and (2) green covers, both implemented in agricultural areas on the hillslopes, and (3) stream restoration in the channels. We evaluated the potential of these NBS to reduce surface runoff, flood discharge, soil erosion and sediment yield, which are all projected to be negatively impacted by climate change due to an increase of extreme precipitation. The evaluated NBS are shown to be a cost-effective climate change adaptation strategy in Mediterranean catchments. This work has been financed by ERDF/Spanish Ministry of Science, Innovation and Universities—State Research Agency/Project PID2019-109381RBI00/AEI/10.13039/501100011033 (XTREME) under the National Program for Research, Development and Innovation focused on the Societal Challenges