Exposed Built-Up Lands Grew Faster than Total Flood Areas in China During 2000–2020

Abstract Exposed built-up land in flood areas is a vital indicator determining flood losses. It potentially changes in the context of rapid urbanization and climate change particularly in hotspot countries like China. However, a comprehensive understanding of the spatiotemporal patterns of flood extent and exposed built-up lands is hampered due to limited information of historical floods. To fill the research gap, this study developed the Spatial Dataset of Historical Floods in China (SDHFC) with event-explicit exposure from 2000 to 2020 using Google Earth Engine, based on internationally available flood event inventories and remote sensing-based surface water data. The Mann-Kendall test and rectified Theil-Sen trend analysis were applied to quantify the changes in flood extent and exposed built-up lands. The SDHFC delineated the inundation extent for 212 flood events in China during 2000–2020, demonstrating a notable improvement compared with global database. Both flood extent and exposed built-up lands increased significantly, with the latter growing at a rate of 9.65%·a -1 , approximately 1.8 times that of the former. Continuous expansion of built-up lands was identified as the primary driver (62%) for the rapid increase in their exposure to floods, much higher than the contribution of the observed flood extent (38%). The findings are crucial for understanding the complex interactions between flood patterns and urbanization processes in China in 2000–2020. The methodology could be applied in various regions for investigating long-term sequences of flood extent and exposed built-up lands.