Pathways of ecosystem-based disaster risk reduction: A global review of empirical evidence

Ecosystems provide valuable services in reducing the risks of disasters through various pathways, which are increasingly recognized as sustainable strategies for disaster management. However, there remains limited information on the underlying ecological processes of risk reduction. This paper addresses this gap by synthesizing ecological mechanisms and evaluating the 'level of evidence' and 'scale of use' through a review of 64 peer-reviewed research articles published between 2015 to 2022. These research articles covered nine types of disasters, predominantly floods (42.19 %), followed by urban heat waves (18.75 %), storm runoff (10.94 %), coastal erosion (9.38 %), tsunamis (4.69 %), and avalanches and landslides (6.25 % each). The level of evidence supporting ecological processes for disaster risk reduction is moderate, as is the 'scale of use'. Results show that there are a few studies describing the mechanism of ecosystem-mediated risk reduction and are mostly limited to the causal relationship. Empirical evidence demonstrates that forest and freshwater ecosystems buffer the risk of urban heat through processes such as transpiration, solar radiation interception, and evaporative cooling, while flood risks are mitigated by enhancing evapotranspiration, reducing water runoff time, and facilitating infiltration rates. Coastal erosion is reduced by dissipating wave energy and through beach nourishment, which facilitates ecological succession. The review underscores that hazard attenuation depends on factors such as forest type (e.g., species composition, age structure, and area), and landscape characteristics (e.g., matrix, composition and configuration). Moreover, the geographic scope of published research is largely confined to developed countries and the global north. Multidisciplinary research involving ecologists and disaster experts is imperative to address existing knowledge gaps and enhance the integration of ecosystem-based adaptation into disaster risk reduction strategies.

Economic valuation of ecosystem-based rockfall risk reduction considering disturbances and comparison to structural measures

Forests provide a series of ecosystem services, including the protection from natural hazards. Thanks to these forests, structural protection measures can be avoided in many places. A realistic long-term valuation of this ecosystem-based risk reduction provided by the forest is essential. The aim of this study is to assess the Net Present Value (NPV) of a protection forest using a risk-based approach and compare it to the NPV of rockfall nets. Costs to be included in the NPV calculation are forest management interventions, net construction, and benefits are the risk reduction and wood sales. The risk reduction is monetised as avoided costs, i.e. the difference between the yearly rockfall risk with and without measure. Uncertainties in the protection effect due to possible forest fires were simulated over a period of 100years using a Monte-Carlo approach. Both the protection forest and the nets effectively reduce rockfall risk at the study site. The NPV of the nets is highly negative (-124,100 CHF/ha), indicating that they are economically not worthwhile at the study site. The NPV of the protection forest is highly positive (162,400 CHF/ha). The variation of the NPV due to fires is very low and the influence of this disturbance on the long-term efficiency of the protection forest is small. Building temporary nets in case of a large fire can restore the protective effect. Their NPV is, however, lower compared to the situation without net. By calculating the NPV of a forest considering its risk reducing effect, we provide a methodology for a realistic valuation of its protective effect. It is based on a case study, which, however, can be applied in a broader context. The presented approach can serve as basis to find optimal combinations of investment in natural hazard prevention, be this ecosystem-based or structural measures.

The Potential Role of Tree Diversity in Reducing Shallow Landslide Risk

Recently, interest in utilizing ecosystems for disaster risk reduction has increased, even though there remains considerable uncertainty regarding the role of ecosystems in buffering against natural hazards. This ecosystem role can be considered an ecosystem service. Although a strong body of evidence shows that biodiversity enhances ecosystem services, there are only a few studies of the relationship between biodiversity and the role of the ecosystem in reducing the risk of natural disasters. To explore the desired state of an ecosystem for disaster risk reduction we applied the finding that biodiversity enhances ecosystem services to evaluate the role of woody vegetation in reducing the frequency and severity of shallow landslides. Using information related to shallow landslides and woody vegetation in Japan as a case study, we compared the severity of shallow landslides (i.e., landslide volume) with tree species richness. Although we provide no direct evidence that tree species richness reduces shallow landslide volume, we found that the predictability of the model, which evaluated relationships between landslide volume and environmental variables in watersheds throughout the Japanese Archipelago, increased with tree species richness. This finding suggests that biodiversity is likely associated with shallow landslide risk reduction, emphasizing a possible reduction of spatial and temporal uncertainty in the roles of woody vegetation. Our study identifies a need for socioecological systems to build new approaches found on the functionality of such ecosystems.