Nature Based Solutions to mitigate the devastating impacts from extreme weather and climate change (XTREME)

To get a full understanding of the impacts of global change on the catchment-scale sediment balance, models are needed that combine hillslope soil erosion processes with channel morphodynamics. Here we present a modification to the SPHY-MMF model that includes a novel channel morphodynamics module, which determines erosion and deposition in rills and channels. We applied the model to a Mediterranean study area in southeast Spain, in which we show that channel erosion contributes substantially (35%–40%) to the total sediment yield, highlighting the importance of accounting for channel erosion in catchment-scale sediment budget estimations. The climate change scenarios show that the different erosional processes (i.e. sheet, rill, channel) are projected to decrease or increase, depending on the projected change in annual and extreme precipitation. From this we conclude that interactions between different erosional and depositional processes should be considered when studying the impact of global change on the catchment-scale sediment balance.

Climate change is expected to lead to increased soil erosion in many locations worldwide affecting ecosystem services and human well-being. Through a systematic review of 224 modelling studies, we provide a global assessment of the impact of climate change on soil erosion and the adaptation potential through land use change and soil conservation. We account for the robustness of each study based on a statistical analysis of ten methodological aspects and an expert consultation. Results show a global increasing trend in soil erosion towards the end of the 21st century, with the highest increase projected in semi-arid regions. Land use change characterized by agricultural expansion and deforestation aggravate the impact. Reforestation, agricultural land abandonment and soil conservation practices can entirely compensate the impact of climate change on soil erosion. This stresses the need for soil conservation and integrated land use planning. From the obtained weights per study we can conclude that there is a lot of uncertainty in the methods applied, without a clear trend towards more robust studies. Based on the results of the expert consultation, we recommend to use a climate model ensemble of at least five climate models, based on the latest CMIP6 climate scenarios. These data should be downscaled and bias corrected using trend preserving quantile methods. Finally, the post-processed climate data should be applied in a soil erosion model forced by precipitation and runoff. Considering the most robust methodologies of the different aspects of the uncertainty cascade will lead to better spatial evaluation of the impact of climate change on soil erosion and identification of most effective adaptation strategies.

Worldwide, Mediterranean cropping systems face the complex challenge of producing enough high-quality food while preserving the quantity and quality of scarce water for people and agriculture in the context of climate change. While good management of nitrogen (N) is paramount to achieving this objective, the efficient strategies developed for temperate systems are often not adapted to the specificities of Mediterranean systems. In this work we combined original data with a thorough literature review to highlight the most relevant drivers of N dynamics in these semiarid systems. To do so, we provide an analysis at nested scales combining a bottom–up approach from the field scale with a top–down approach considering the agro-food system where cropping systems are inserted. We analyze the structural changes in the agro-food systems affecting total N entering the territory; the contrasting response of yields to N availability under rainfed and irrigated conditions in a precipitation gradient; the interaction between N management and climate change adaptation; the main drivers affecting the release of Nr compounds (NO3-, NH3, NO, N2O) as compared with temperate systems; and finally, the behavior of N once exported to highly regulated river networks. We conclude that a sustainable N management in Mediterranean cropping systems requires the specific adaptation of practices to the particular local agroenvironmental characteristics with special emphasis on water availability for rainfed and irrigated systems. This approach should also include a systemic analysis of N inputs into the territory that are driven by the configuration of the agro-food system.