An integrated method to account for river flood mitigation service in the SEEA-EA framework

The United Nations System of Environmental-Economic Accounting Ecosystem Accounting (SEEA-EA) aims to quantify the contributions of ecosystems to economies and incorporate the contribution of nature into economic decision-making. However, a key challenge for the SEEA-EA ecosystem service (ES) accounts is distinguishing the actual use from potential supply, especially for regulating services like river flood mitigation service, and connecting it to different beneficiaries in a consistent unit. To address this challenge, integrated models method for river flood mitigation service accounts within the SEEA-EA framework was proposed to incorporating beneficiaries. The method comprises four steps: 1) determining serviceshed, service providing areas and service benefiting areas, 2) assessing potential ecosystem flood mitigation service, 3) simulating spatial flow, connecting it with beneficiaries, and valuation, and 4) compiling Supply and Use table of actual use in alignment with SEEA-EA framework. We applied this framework to the flood-prone Wanquanhe Basin on Hainan Island, China, to assess flood mitigation service provided by forest ecosystems (e.g., natural forests, rubber, and gardens) and the Niululing Reservoir. The SWAT and Random Forest models estimated potential ES, land use maps identified beneficiaries, and the HEC-RAS model simulated the spatial flow of floodwater. Data from these models were then integrated to quantify the ES actual use, which were subsequently incorporated into the SEEA-EA accounts. The case study revealed that in 2020, the upstream forest ecosystems and the reservoir provided 15.52 and 2.9 billion Yuan worth of actual flood mitigation service, respectively, to downstream beneficiaries. This study demonstrates how our integrated models method for river flood mitigation service effectively distinguishes between potential and actual ES use, connects services to beneficiaries, and constructs comprehensive SEEA-EA accounts. This method can be replicated in other regions to compile SEEA-EA accounts for river flood mitigation service, which can inform nature-based decision-making for flood risk management.