Assessing relative wetland flood risk management benefits using COPE : an exploration of Capacity, Opportunity, Payoff, and Efficacy

Wetlands reduce flood risk, but measuring their performance and benefits is challenging due to the highly variable nature of the factors, including landscape features, land use, and climate, that shape flood response. An evidence-based index was developed to rapidly assess the potential flood risk management benefits of wetland restoration. These benefits are measured by combining the Capacity (C), Opportunity (O), Payoff (P), and Efficacy (E) indicators into a single index, called COPE. Capacity captures the internal wetland characteristics that alter flood peak attenuation potential. Opportunity reflects watershed characteristics that control the effectiveness of internal wetland capacities. Payoff quantifies the population exposed to high flood risk, and Efficacy reflects the ability of communities to respond to flooding. Literature evidence for the C and O indicators suggests that flood risk is reduced by increasing wetland storage in small basins with hillslopes or in moderate to large riverine basins. Literature evidence for the E index suggests that multiple indicators can capture the potential for disproportionate harm to vulnerable communities. A case study demonstrated that the P indicator strongly influences the relative-benefits score produced by COPE, but the C, O, and E indexes can alter the score substantially when values deviate from average conditions.