Spatio-temporal changes in rice area at the northern limits of the rice cropping system in China from 1984 to 2013

Rice area has been expanding rapidly during the past 30 years under the influence of global change in northeastern China,which is the northernmost region of rice cultivation in China. However,the spatio-temporal dynamic changes in rice area are still unclear,although they may have important policy implications for environmental protection and adaptation to climate change. In this study,we aimed to identify the dynamic changes of the rice area in Heilongjiang Province of northeastern China by extracting data from multiple Landsat images. The study used ground quadrats selected from Google Earth and the extraction of a confusion matrix to verify the accuracy of extraction. The overall accuracy of the extracted rice area was higher than 95% as a result of using the artificial neural network(ANN) classification method. The results showed that the rice area increased by approximately 2.4×106 ha during the past 30 years at an annual rate of 8.0×104 ha,and most of the increase occurred after 2000. The central latitude of the rice area shifted northwards from 46 to 47°N during the study period,and moved eastwards from 130 to 133°E. The rice expansion area accounted for 98% of the total change in rice area,and rice loss was notably rare. The rice expansion was primarily from dryland. In addition,rice cultivation in marshland and grassland played a minor role in the rice expansion in this region.