Quantifying and valuing forests as a nature-based solution for ecosystem-based disaster risk reduction: A systematic review

Forests play a significant role in mitigating natural hazards and are increasingly recognized as nature-based solutions (NBS) for ecosystem-based disaster risk reduction (Eco-DRR). However, their protective effects remain under-quantified, limiting their integration into mainstream risk management practices. This systematic review investigates the current state of quantitative and monetary assessments of forests as Eco-DRR measures. To this end, we focused exclusively on studies reporting quantitative outcomes for forests across a broad range of gravitational and hydroclimatic hazards. The review aims to: 1) provide a comprehensive overview of the concepts and methodologies used to quantify the protective effects of forests; 2) summarize and analyze quantitative evidence and its variation across forest types, methodologies and hazard types; 3) identify research gaps; and 4) synthesize a conceptual framework to facilitate further research. We screened 3568 papers, from which 77 studies were selected, comprising 155 data points. Drawing on the insights from these studies, we developed a conceptual framework to guide future research in this field. Methodologies for the quantification of protective effects were categorized into three main groups: hazard-based, risk-based, and economic valuation methods, with hazard-based approaches being the most frequently applied, followed by economic valuation. Reported monetary values for forest protective effects varied significantly, ranging from less than 1 USD to over 41,000 USD per hectare per year. We investigated potential sources of this variation, including forest type, hazard type, and the methodologies employed. Our findings underscore the need for more robust hazard models tailored to specific hazard types that integrate forest characteristics, climate change impacts, and post-disturbance forest recovery. We emphasize the importance of applying risk-based methods when evaluating the protective effect of forests. To this end, the review provides a framework to guide future efforts and support the integration of forests into disaster risk reduction and climate adaptation strategies.