A cost‐benefit analysis of afforestation as a climate change adaptation measure to reduce flood risk

Abstract

Increased river flood frequency is considered a major risk under climate change. Protecting vulnerable communities is, therefore, a key public policy objective. Natural flood management measures (NFM)—notably re‐afforestation on hillslope and floodplain—are increasingly discussed as cost‐effective means for providing flood regulation, particularly when considering ecosystem services other than flood regulation. However, studies that place flood benefits alongside other benefits are rare, potentially causing uncertainty in policy decision‐making. This paper provides a cost‐benefit analysis of the impacts of afforestation on peak river flows under UKCP09 climate change projections, and on additional ecosystem services in a rural catchment in Scotland. We find significant positive net present values (NPV) for all alternatives considered. However, benefits are dominated by ecosystem services other than flood regulation, with values related to climate regulation, aesthetic appeal, recreation and water quality contributing to a high positive NPV. The investment in riparian woodland (under low and central climate change scenarios) delivers a positive NPV alone when considering flood regulation benefits only. The case study suggests that afforestation as a sole NFM measure provides a positive NPV only in some cases but highlights the importance of identifying and quantifying additional ecosystem co‐benefits.

Natural flood management, lag time and catchment scale: Results from an empirical nested catchment study

“…This suggests that while such interventions could be complementary to the installation of debris dams and holding ponds (Metcalfe, Beven, Hankin, & Lamb, 2017a; Odoni & Lane, 2010), as part of a “catchment systems engineering” approach (Hewett, Wilkinson, Jonczyk, & Quinn, 2020) their impacts, and the associated return on investment may remain much less clear until NFM schemes have been in operation for multiple decades (Bogena, White, Bour, Li, & Jensen, 2018). By contrast, Dittrich et al (2018) showed through modelling that widespread afforestation of the Eddleston catchment as a single management strategy could deliver significant cost benefits for flood risk reduction and especially other complementary ecosystem services.…”

Modelling and Evaluation of the Effect of Afforestation on the Runoff Generation Within the Glinščica River Catchment (Central Slovenia)

“…Costs and benefits are calculated with the most recent available prices of elements included in the CBA and explained in the following paragraphs. The discount rate applied, which takes into consideration how much someone prefers benefits now rather than in the future, was 4% because similar values were adopted in other studies [4]. It is known from previous studies such as Dittrich et al [4] that ecosystem services (ES), such as biodiversity, usually represent also a significant portion of the beneficial character of afforestation measures.…”

“…Despite this growing interest in NWRMs, economic appraisals of the flood protection benefit of afforestation measures are rare. Dittrich et al [4] undertook a detailed cost-benefit analysis of afforestation as a climate change adaptation measure and highlighted the importance of identifying and quantifying additional ecosystem co-benefits of NWRMs. As a result of the limited hydrological and economic appraisals of NWRM, the overall aim of this study is to enhance the knowledge base associated with flood risk and impacts.…”

Spatial assessment of flash‐flood vulnerability in the Moldova river catchment (N Romania) using theFFPI

“…The analysis carried out in this study is based on a compilation of geospatial and hydrological information. The methodological development consists of three stages, the collection of geospatial data and their processing, the steps to calculate the Flash Flood Potential Index (FFPI) and finally the validation of the results, which consists in the analysis of the obtained outputs, compared to the phenomenological recordings of floods and the impact of forest loss, especially in the upper part of the catchment, where it recorded the highest values (Andronache et al, 2017;Dittrich, Ball, Wreford, Moran, & Spray, 2018). Most of the factors were derived from the Digital Elevation Model (DEM), extracted from the EU-DEM dataset, available to download from the European Environment Agency.…”