Nature-based solutions in mountain catchments reduce impact of anthropogenic climate change on drought streamflow

Adapting to climate change through Nature-Based Solutions can reduce the severity of hydrological droughts caused by human influence on the climate, according to a multi-model joint-attribution of climate and landscape-vegetation states developed in South Africa. Quantifying how well Nature-based Solutions can offset anthropogenic climate change impacts is important for adaptation planning, but has rarely been done. Here we show that a widely-applied Nature-based Solution in South Africa - invasive alien tree clearing - reduces the impact of anthropogenic climate change on drought streamflow. Using a multi-model joint-attribution of climate and landscape-vegetation states during the 2015-2017 Cape Town "Day Zero" drought, we find that anthropogenic climate change reduced streamflow by 12-29% relative to a counterfactual world with anthropogenic emissions removed. This impact on streamflow was larger than corresponding reductions in rainfall (7-15%) and reference evapotranspiration (1.7-2%). Clearing invasive alien trees could have ameliorated streamflow reductions by 3-16% points for moderate invasions levels. Preventing further invasive alien tree spread avoided potential additional reductions of 10-27% points. Total clearing could not have offset the anthropogenic climate change impact completely. Invasive alien tree clearing is an important form of catchment restoration for managing changing hydroclimatic risk, but will need to be combined with other adaptation options as climate change accelerates.