Nature-based solutions’ co-benefits beyond risk reduction: a review of assessment methods

Nature-based solutions (NbS) can considerably reduce risks arising from weather extremes for society, and in addition provide multiple societal and environmental co-benefits. NbS are typically designed by the public sector, but the private sector, such as the financial sector, could also contribute to the finances needed to enable NbS uptake. However, a barrier to these investments and NbS implementation is the challenge to quantify NbS co-benefits. Through a systematic literature review, we investigate the methods available for evaluating co-benefits of NbS, beyond risk reduction. We examine their strengths and weaknesses in order to assess their applicability in the broader context of nature-based insurance and investment solutions. The review identified several (economic and non-economic) methods available that can provide a (semi-)quantitative assessment of co-benefits, with different levels of overall effort and knowledge requirements. The study showed there is no single method that is widely used to assess a specific co-benefit or NbS. Critical aspects of NbS co-benefits assessment arise from the temporal and spatial scales covered, and data availability. Previous work has been predominantly context-specific and applied to specific cases, but in principle the methods applied are replicable and scalable to different contexts. Most of the methods showed the possibility of identifying multiple co-benefits and dealing with possible disbenefits. A key limitation identified in the reviewed papers is the lack of consideration of impacts of future climate change on the NbS. We discuss challenges and advantages of the applied methods to facilitate the integration of a more comprehensive assessment of NbS co-benefits in a broader context that could help to overcome some issues and strengthen a robust evidence base for NbS performance.