Revealing Annual Crop Type Distribution and Spatiotemporal Changes in Northeast China Based on Google Earth Engine

Abstract

Northeast China (NEC) produces 1/4 of the grain and 1/3 of the commercial grain in China, and is essential for food security and a sustainable socio-ecological system development. However, long-term annual crop type distribution in this vital area remains largely unknown, compromising the scientific basis for planting structure adjustment and sustainable agriculture management. To this end, we integrated 111-dimensional MOD09A1 features, feature optimization and random forest algorithms on the Google Earth Engine (GEE) platform to classify annual crop types in the NEC during 2000–2020, and adopted multi-source spatial data and geostatistical methods to reveal anthropogenic and natural characteristics of crop type changes. The results demonstrated that sample-based classification accuracies were 84.73–86.93% and statistics-based R2 were 0.81–0.95. From 2000–2020, the sowing area of maize and rice increased by 11.92 × 106 ha (111.05%) and 4.03 × 106 ha (149.28%), whereas that of soybean and other crops decreased by 13.73 × 106 ha (−64.10%) and 1.03 × 106 ha (−50.94%), respectively. Spatially, maize expanded northwestward, rice expanded northeastward, and soybean demonstrated a south-north shrinkage. The soybean-to-maize shift was the main conversion type, and its area largely reduced from 8.68 × 106 ha in 2000–2010 to 4.15 × 106 ha in 2010–2020. Economic comparative benefit and climate change jointly affected crop types in NEC. Higher-benefits maize and rice were mainly planted in more convenient areas with more population and closer to settlements, roads and waterways. The planting of maize and rice required higher temperature and precipitation, and climate change in the NEC provided favorable conditions for their expansion toward high-latitude areas. The crop type changes in the NEC have boosted economic benefits, but increased water–carbon–energy costs. Thus, effective measures such as subsidy policies, ecological compensation, and knowledge-exchange should be implemented to aid crop type and rotation adjustment and ensure food-ecological security.