Cost–benefit analysis of mangrove ecosystems in flood risk reduction: a case study of the Tana Delta, Kenya

Mangrove ecosystems are one of the most valuable and productive coastal ecosystems and provide a wide range of ecosystem services. These services are of value to local, national, and international communities and include provisioning (fuel wood, timber, poles, posts, charcoal, and nonwood products—such as food, thatch, fodder, medicine, and fisheries), regulating (carbon sequestration, shoreline protection, and erosion control), supporting (by providing a habitat conducive to biodiversity), and cultural (recreation, esthetic, and tourism) (Barbier et al. 2011; FAO 2007; Kirui et al. 2013). Despite these invaluable services, mangroves are one of the most threatened ecosystems in the world and are declining globally at an annual a rate of 1–2% (FAO 2007). Mangroves along the Kenyan coastal region are estimated to have declined at a rate of 0.7% per year between 1985 and 2010. The decline was accelerated by the overharvesting of mangrove wood products, conversion to other land uses, and legislative inadequacies (Kirui et al. 2013). The degradation of ecosystems undermines their resilience and threatens the continuous supply of ecosystem services. It is estimated that mangrove deforestation generates 0.02–0.12 Pg carbon per year in emissions and constitutes approximately 10% of the total emissions from global deforestation (Donato et al. 2011). A degraded ecosystem continuously increases a community’s vulnerability and exposure to hazards because the ecosystem’s capacity to meet people’s needs decreases (Colls et al. 2009; Gandage and Ranadive 2009; Munang et al. 2013). Mangrove forest Abstract Mangrove ecosystems are valuable and productive coastal ecosystems that provide several ecosystem services. Nevertheless, trivialization of the value of mangrove ecosystems has led to their decline at an annual global rate of 1–2%. Degradation undermines the resilience of these ecosystems and threatens the continuous supply of goods and services that they provide. Diverse mangroves that contribute to the well-being of coastal communities characterize Kenya’s coastal region. Despite their importance, 0.7% of the mangroves are destroyed annually. In this study, the value of mangroves with regard to coastal flood risk reduction was estimated via a case study of the Tana Delta, Kenya. The valuation was calculated using the total economic value framework where both direct and indirect use values that influence flood risk are calculated using flood-avoided damage approach and local market prices. For comparative purposes, all the estimates presented in this paper were standardized to the 2015 US$/ha equivalent value using the United States Consumer Price Index for all urban consumers. The net value of mangroves for flood reduction was estimated to be between US$238/ha/yr and US$311/ha/yr. The skewed distribution was largely attributed to a variation in flood frequency and mangrove forest density.