A Novel Framework for the Assessment of the Nature-based Solutions (NbS) Effectiveness in the Reduction of Hydro-Meteorological Risks

The identification of suitable and common methods and tools to evaluate the effectiveness of Nature-based Solutions (NbS) as adaptation measures for hydro-meteorological risks still remains an open challenge. NbS effectiveness is a complex concept whose evaluation needs to take into account also the reduction of the exploitation of both natural and economic resources, the achievement of the implementers’ and stakeholders’ intent at the design phase, and the provision of co-benefits. The following contribution aims to integrate the NBS concept in a novel hydro-meteorological risk framework reported by Brogno et al. (2024) 1. Starting from Crichton’s Risk Triangle, the framework allows the estimate of the risk as the sum of the economic losses and equivalent CO2 emissions resulting from hazardous events that may affect the healthcare system, social relationships, ecosystems, agro-food production, infrastructure safety, and cultural and natural heritage. The final output as a cost per day is a quantitative and pragmatic estimate to facilitate the decision-making process. In addition to presenting the framework, this contribution aims to show practical examples of how the proposed framework can be adopted as a tool for the assessment of NbS effectiveness in hydro-meteorological risk reduction. In particular, bio-geophysical quantities can be used to integrate the contribution of NBS intervention as a local modification of both the hazard characteristics and the predisposition of the exposed elements to be affected by the occurrence of hazardous events. These bio-geophysical quantities need to be directly influenced by NbS and affect in turn the targeted risk processes. The framework can also include the NbS life cycle into the risk assessment, accounting for the greenhouse gas emissions along with the implementation, maintenance, and restoration costs resulting from an NbS intervention. The comparison of the average framework outputs over several hazardous events before and after an NbS intervention can provide an assessment of the long-term NbS effectiveness. 1 Brogno, L., Barbano, F., Leo, L. S., Di Sabatino, S., (2024). A novel framework for the assessment of hydro-meteorological risks taking into account nature-based solutions. Environmental Research Letters, 19(7), DOI: 10.1088/1748-9326/ad53e