Trends in vegetation productivity related to climate change in China’s Pearl River Delta

million and 123 cities with between 1 and 10 million, almost 63% of the population was still non-urban in 2015 [19]. If all PRD cities are considered as one entity, the PRD overtook Tokyo as the world’s largest megacity in both size and population, in 2010 [20]. Accompanying this growth has been a dramatic deterioration in air quality, although no data indicating long- term trends are available. The study area comprises the 11 PRD prefectures of Hong Kong, Macau, Shenzhen, Guangzhou, Dongguan, Shunde, Jiangmen, Foshan, Zhongshan, Huizhou and Zhaoquing (Fig 1). A land use land cover (LULC) map from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images indicate approximately 9% urban/built- up, 31% cropland including tree cultivation, and 45% forest (Fig 1). Rice, with two crops a year occupies 76% of agricultural land, with the early crop from March to July and the late crop from July to November. Often this will be followed by a vegetable, winter wheat, or rapeseed. In addition, much of China’s output of sugarcane is produced in the region. Other agricultural products include sweet potato, vegetables, citrus fruits and tea. With increasing industrializa- tion, more land has been converted to cash crops and vegetables, and grain production has intensified recently. This small PRD region, only 0.4% of China’s land area, now accounts for 10% of China’s gross domestic product (GDP). The climate of the PRD is tropical, with hot and humid summers from June to August, with approximately 2500 mm rainfall between

Fig 1. Location map of the study area and spatial distribution of land use land cover classes [21]. https://doi.org/10.1371/journal.pone.0245467.g001 PLOS ONE Climate and vegetation trends in the Pearl River Delta PLOS ONE | https://doi.org/10.1371/journal.pone.0245467 February 24, 2021 3 / 20