Abstract
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.
Highlights
Quantifying how well Nature-based Solutions can offset anthropogenic climate change impacts is important for adaptation planning, but has rarely been done
We used two main metrics to quantify the impact of anthropogenic climate change (ACC) on drought-period streamflow and the difference that invasion or clearing could have had on this impact: (i) QR%, which is the percentage of reference state (Natural Current) drought-period streamflow realised for each comparator state (Actual Current, -Cleared, -Invaded); and (ii) QR% point difference, which is the percentage point difference between the QR% derived for the Actual Current state and that derived for the two other comparator states (Actual Cleared, -Invaded)
Simulations showed that clearing invasive alien tree (IAT) prior to the drought would have likely ameliorated the reductions in drought-period streamflow experienced due to ACC, but that this depended on the extent of invasion (Figs. 4–5 and Supplementary Table 2)
Summary
Quantifying how well Nature-based Solutions can offset anthropogenic climate change impacts is important for adaptation planning, but has rarely been done. Ecosystem management, protection and restoration have been proposed for buffering societies from the increased impact of climate-related extremes due to anthropogenic climate change (ACC)[4–6] These interventions, termed Nature-based Solutions (NbS) for climate change adaptation, are framed as being able to reduce or even offset the impacts experienced from anthropogenic influence on the physical climate system and in particular those impacts related to changing extreme events. Quantitative assessments of the impact of NbS often focus on climate change mitigation potential including how much carbon they can remove from the atmosphere[13–15], or more recently NbS effects on global temperatures[16] These analyses are mostly global despite the scale at which the impacts of ACC on extremes are felt and at which climate adaptation decisions are made. We need methods to be able to quantify the role of ACC in changing extreme event characteristics from a meteorological perspective that can be used to quantify the role that NbS play in moderating this impact
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