The economic value NBS for flood risk mitigation and their benefits in a river basin context: A metaregression-analysis

Nowadays, Nature-Based Solutions (NBS) are high on policy agendas to reduce flood risks and to build a resilient environment. In order to facilitate cost-benefit analysis of investments in NBS, this paper provides a first Meta-Regression Analysis (MRA) function transfer to identify and assess the value of NBS measures for flood risk mitigation in the basin context. Our data are based on 199 observations related to 62 studies conducted in America, Europe, and Asia-Oceania since the mid-1990s. Our estimates show that NBS measures in river streams and floodplains are the most valued and that the primary benefit of water regulation is insignificant. However, individuals value co-benefits such as recreation, aesthetics, food and materials, and the scenario that provides more room for nature in the river basin. The in-sample convergent validity test shows that the average MAPE (Mean Absolute Percentage Error) is around 48% and the median around 17%. In the same vein, the out-of-sample test in the case study of the Brague catchment shows a MAPE of between 5% and 66%. This suggests that the MRA function transfer can reasonably be used to inform policymakers when estimating NBS measures for flood risks.