Tracking spatiotemporal dynamics of irrigated croplands in China from 2000 to 2019 through the synergy of remote sensing, statistics, and historical irrigation datasets

Abstract

Irrigation is widely implemented in China to enhance grain production and ensure food security. Spatiotemporal information on irrigation is critically important, but the existing global and regional irrigation products have a coarse spatial resolution, low accuracy, and short temporal coverage, which is a knowledge gap to be filled. Generating explicit and accurate information on the spatial and temporal extent of irrigation is essential to underpin and facilitate water resource allocation and management, as well as to understand catchment hydrology, and evaluate irrigation infrastructure investment. We proposed a two-step strategy to map annual irrigated areas at 500 m resolution in China from 2000 to 2019. We first generated initial irrigation maps using MODIS data and statistical data (MIrAD-GI). Then we combined MIrAD-GI, the existing irrigation maps, and land use/cover products with irrigation information, into an improved series of annual irrigation maps (IrriMap_Syn) with constrained statistics. Afterwards, pixel-wise accuracy assessment for IrriMap_Syn was conducted in four representative regions in three years. The resultant irrigation dataset performed well with a mean overall accuracy of 0.89 and a kappa coefficient of 0.82. According to our annual irrigation maps, the total irrigated area in China increased by 24.8%, from 52.8 million ha in 2000–65.9 million ha in 2019, at a rate of 690,000 ha per year. Spatially, irrigated croplands increased substantially in North China, especially in Xinjiang and Heilongjiang. Land reclamation largely contributed to the increase in irrigation in North China. A growing population and improved irrigation infrastructure also promoted the increase in irrigated areas. As the first of its kind in the country, our spatially explicit maps of irrigated croplands advance our understanding of the spatiotemporal pattern of irrigation dynamics in China and are expected to contribute to sustainable water resource management and irrigation strategies in the face of climate change.