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

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.