Towards quantitative evidence of Eco-DRR in mountains: A concise review

Worldwide, gravitational natural hazards pose risks to residential areas and infrastructures in mountainous, but also in other relief-rich areas. To protect against those hazards, nature-based solutions, also called ecosystem-based disaster risk reduction (DRR) measures, are increasingly used in addition to, or as replacement of, more classical engineered structures. Quantified evidence of the net benefit of specific protective functions of nature-based measures can likely facilitate financial and organisational resources required for ensuring the durability and implementation at scale of Eco-DRR measures. In this review, we summarise existing studies that demonstrate the efficacy and benefit of Eco-DRR measures against gravitational natural hazards and propose a framework for providing quantitative evidence of natural hazard risk reduction provided by Eco-DRR in mountains. A realistic valuation of the benefits of Eco-DRR measures in mountains is only possible if, firstly, their effects on the natural hazard processes are quantified with sufficient detail and finally expressed in monetary terms allowing for a cost-benefit analysis and, secondly, possible temporal variations and uncertainties regarding the state and development of the Eco- DRR measure are taken into account. The protection from natural hazards is a so-called regulation function provided by ecosystems and is a “non-market good” as its benefit cannot directly be converted into monetary terms. The valuation of the benefits of this function can be done with a replacement cost methods, a hedonic pricing method, a contingent valuation method or an avoided cost method. This review shortly explains these methods and provides examples of applications to Eco-DRR in mountains. Finally, we propose a framework based on a risk-based approach allowing for the translation of the physical, protective effect of a Eco-DRR measure on the natural hazard process into a reduction of the risk of fatalities as well as of property risks in terms of the avoided costs.