High-resolution mapping of China's flooded croplands.

Abstract

Climate change and the increasing frequency of floods have undermined China's food security. Creating detailed maps of flooded croplands is essential to improve prevention and adopt effective adaptation initiatives. Previous large-scale flood mapping efforts were hampered by limited meteorological and hydrological data, and the susceptibility of optical satellite images to cloud cover, leading to high uncertainty when downscaled to the cropland-scale. Here, using 4968 near-real-time (NRT) Sentinel-1 SAR (S1) images (spatial resolution: 10 m), we generated China's first set of high-resolution flooded cropland maps covering the period from 2017 to 2021. Our results demonstrate that croplands accounted for 43.8% to 49.8% of China's total flooded areas (ranging from 82,175 km² to 122,037 km²). We also created high-resolution flood maps specifically for rice and maize crops. The inundated rice areas ranged from 8428 km² to 22,123 km², accounting for 22.34% to 41.91% of the annual flooded croplands, or 2.82% to 7.45% of the annual rice cropland. In comparison, the inundated maize cropland fluctuated from 2619 km² to 5397 km², representing 5.38% to 13.56% of the annual flooded croplands. Our findings revealed extensive floods in rural areas, highlighting the urgent need to prioritize flood prevention and mitigation efforts in such regions. In light of China's allocation of an additional 1-trillion-RMB treasury bonds for water infrastructure projects, the high-resolution flood maps can be used to select sites for flood control projects, and evaluate the impact of flooding on crop yields and food security, thus targeting poverty alleviation in rural areas of China.