CCWEM and CCWIF: 10 m Datasets of Coastal Wetland Extent and Inundation-Frequency Gradients across China

Abstract. Coastal wetlands are critical ecological spaces for coastal-zone management, with direct implications for wetland conservation, shoreline regulation, and nearshore spatial planning. Here, we present two complementary 10 m datasets for China's coastal wetlands in 2025: the China Coastal Wetland Extent Map (CCWEM) and the China Coastal Wetland Inundation Frequency Map (CCWIF). CCWEM delineates the maximum wetland extent along the Chinese coast, whereas CCWIF further characterizes internal inundation-frequency gradients within this extent. To generate CCWEM, we constructed a four-season semantic segmentation dataset based on multi-season Sentinel-2 observations and developed SeasonMamba, which integrates shared encoding, seasonal adaptive fusion, and pseudo-MSIC representation learning to achieve stable delineation of coastal wetlands under varying seasonal and tidal conditions. To generate CCWIF, the Chinese coast was divided into 58 tidal subregions to account for spatial heterogeneity in tidal environments, and a region-specific inundation-frequency estimation workflow was developed by integrating Sentinel-2 MNDWI time series with tide gauge observations. CCWEM mapped 8906.15 km² of coastal wetlands and achieved an overall accuracy of 94.07 %, with an F1 score of 94.83 % in low-tide boundary validation. Independent validation using Sentinel-1 observed water occurrence showed overall monotonic agreement with the CCWIF classes across all validation regions combined (Spearman's ρ = 0.756), supporting its ability to characterize relative inundation-frequency gradients. To our knowledge, CCWIF provides the first national-scale dataset describing coastal wetland inundation-frequency gradients across China. Together, CCWEM and CCWIF provide a consistent high-resolution spatial dataset for characterizing both the extent and internal hydrological structure of China's coastal wetlands, supporting coastal wetland monitoring, assessment, and management under complex tidal conditions.