Four Decades of Land Use Change and Ecosystem Service Value Dynamics in the Flood Detention Areas of the Haihe River Basin, China

Flood detention areas (FDAs) are essential components of basin-scale flood risk management, but they represent particularly critical conflict zones between socioeconomic development and flood safety in highly urbanized basins dominated by major metropolitan areas, such as the Haihe River Basin (HRB). These tensions are primarily manifested through land use transitions, yet the long-term dynamics of land use and associated ecosystem service value (ESV) remain insufficiently understood on an annual scale. Based on 30 m annual land use data, we assessed all 28 FDAs in the HRB from 1985 to 2024 using a regionally adjusted equivalent factor method. Cropland remained the dominant land use type but declined from 9217 to 7870 km2, whereas impervious surfaces increased from 1198 to 2417 km2. Equivalent-factor-based ESV exhibited marked fluctuations and decreased from 83.82 × 108 CNY in 1985 to 75.91 × 108 CNY in 2024. Overall ESV declined by 9.43%, but its drivers varied among periods. Changes in valuation coefficients dominated ESV dynamics before 2015, whereas land use change became the dominant driver after 2015, during a period of continued cropland loss and impervious-surface expansion. Despite substantial improvements in water-body ecosystem services driven by ecological water replenishment policies, the overall ESV of FDAs in the HRB declined by 9.43%, mainly due to cropland conversion to impervious surfaces, potentially increasing flood risks. These findings reveal a transition from cropland-dominated service accounting towards joint support by cropland and water bodies, and provide a quantitative basis for differentiated land use management and ecological restoration across individual FDAs.