Compound Seawater Inundation Risks and Soil Carbon Losses under Climate Change and Human Activities

Under global warming, accurately assessing the impacts of future seawater inundation on coastal wetland land use and carbon storage is crucial for climate adaptation and resilience enhancement. Existing studies often fail to comprehensively account for the combined effects of climate change and human activities, with limited attention to soil organic carbon (SOC) loss and the effectiveness of ecological protection measures in mitigating intensified seawater intrusion. This study constructed a comprehensive inundation risk assessment framework that integrates climatic and anthropogenic drivers to evaluate the compound extreme inundation risks and their effects on land use types, SOC storage, and economic value loss under different scenarios for 2035 and 2050 in the Yellow River Delta (YRD). The results indicate that (a) the average annual subsidence rate in the YRD is −41.2 mm, with local peaks reaching −267.5 mm. Regions of high subsidence strongly correlate with areas of petroleum and brine extraction. (b) Rising sea levels lead to higher extreme water levels and shorter recurrence intervals. By 2050, the peak of these extreme water levels is expected to reach 3.88 m, with 50-year events occurring every 6 to 8 years. The maximum inundation distance for 100-year events will be 34.9 km. (c) Loss rates of salt pans, aquaculture ponds, and tidal flats exceed 70% under various recurrence periods of inundation. SOC losses are projected to reach 25.3% to 32.6% in 2035 and 27.1% to 35.3% in 2050, corresponding to economic value losses of 3.86 to 4.72 and 4.03 to 4.98 billion yuan, respectively.