Detection of paddy rice cropping systems in southern China with time series Landsat images and phenology-based algorithms

Abstract

ABSTRACT Southern China is a major rice-producing region where mixed rice cropping systems (single cropping rice (SCR) and double-cropping rice (DCR)) are widely practiced. An accurate estimation of the spatiotemporal changes in cropping systems is important for understanding the dynamic of paddy rice system and for developing suitable agricultural policies. However, few studies focus on mapping long-term changes in cropping systems in this subtropical region. The objective of this research is 1) to improve the phenology- and pixel-based paddy rice mapping (PPPM) algorithm by simultaneously considering the phenology signatures in the rice transplanting and heading periods; 2) to better identify different rice cropping systems and analyze their changes. Based on the improved PPPM method, we generated annual maps of SCR and DCR in southern China with image collection of Landsat 5, 7, and 8 from 1999 to 2019 using the Google Earth Engine platform. The overall accuracies of cropping system results for the study regions range from 81.0% to 98.1% depending on the areas of interest created in our study area. Then, the spatiotemporal patterns of the annual SCR and DCR time series were analyzed. In 2000, the total rice area was 208,614.6 km2, decreased sharply in 2003, and thereafter, the total increase in the paddy rice area fluctuated until 2011. From 2000 to 2019, the total rice area decreased to 171,474.3 km2 in 2019. The results showed that relatively stable SCR mainly distributed in Anhui, Hubei, and Jiangsu provinces whereas DCR occurred in Guangdong, Hunan and Jiangxi provinces. DCR-to-SCR conversion occurred drastically in Hunan, Hubei, and Jiangxi provinces. Rice-to-non-rice conversion was more prevalent in Hunan and Hubei provinces. Detailed spatiotemporal information over 20 years suggested that the plans for agricultural resources utilization in some specific provinces should be proposed, which is of great significance for food security in the major rice-producing area in southern China.