Coastal protection and inland flood mitigation values provided by priority wetland sites in the East Asian-Australasian Flyway

The East Asian–Australasian Flyway connects breeding and wintering grounds for migratory waterbirds across East Asia, South-East Asia and Australasia. Wetlands along the flyway buffer coasts against storm surges, store floodwaters, and sustain globally significant biodiversity. Yet the extent to which sites of biodiversity importance protect people remains unclear. We assessed 41 wetlands in Bangladesh, Cambodia, the Philippines, and Thailand identified as biodiversity priority sites. Using global datasets and hydrological models, we quantified nine biophysical and economic metrics of hazard mitigation, including coastal risk reduction, flood storage, downstream beneficiaries, and economic value of avoided infrastructure damage. Results show that priority sites deliver substantial benefits relative to their extent. Coastal wetlands, especially mangroves in Bangladesh and the Philippines, consistently exceeded national averages for ecological efficiency (% risk reduction and per-hectare avoided damages), though beneficiary numbers varied with settlement patterns. Philippine sites accounted for 12% of the national annual flood-protection value while covering only 3% of the mangrove area, and Bangladeshi sites yielded nearly nine times higher per-hectare values than other mangroves. Inland wetlands showed more variable outcomes: Agusan Marsh and Bueng Boraphet contributed substantial flood storage, while others fell below national averages due to hydrological configuration. Across all metrics, priority sites exceeded national averages in 14 of 36 metric-country combinations, were lower in nine, and did not differ in the remainder. This study provides the first multi-country assessment of how wetlands prioritised for biodiversity contribute to hazard mitigation, using a standardised indicator framework to support integrated conservation and climate adaptation planning.