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

where a small increase is observed over the whole 34 years study period. These image data showing temperature increase distributed evenly over the whole PRD region, are supported by climate station temperature data (S1 Fig) and the rainfall observations are supported by a recent study by Nguyen et al. (2018) [38], who did not observe any significant rainfall trend in this region of China. Rapid urban sprawl, deforestation and browning trends Synchronous to these climatic changes has been a dramatic increase in urbanization in the PRD region. Nighttime lights imagery from the NASA’s National Polar-orbiting Partnership satellite show an increase of 340 to 519 million km2 in illuminated areas in just 20 years from 1992 to 2012 (Fig 3A). This rapid urbanization trend is also evident from browning trends in NDVI and vegetation productivity metrics (Fig 3B and S2 and S3 Figs). Over the past three decades, urban areas in the PRD region quadrupled, with the accelerated growth of small towns into cities and megacities [39]. The amount of urban area grew from 0.5% in 1979 to 10.8% in 2009 [40] by conversion of cropland into urban areas. Displacement of these farm- lands to relatively infertile hilly land away from city centers also resulted in accelerated defor- estation [39,40]. On the maps, these deforestation patches are indicated by pixels showing browning trends (Fig 3B). These regions are adjacent to the urban areas of Huizhou, Dong- guan and Guangzhou, which themselves show significant urban heat island effects [41] in

addition to greenhouse-induced warming. This may partly explain the up to 2˚C increase in temperatures noted above, which is well above the global background warming rate of approx- imately 0.7˚C. Fig 2. Spatial patterns of trends in seasonal and annual temperature and rainfall. Insignificant pixels (p > 0.05) are masked out in grey. https://doi.org/10.1371/journal.pone.0245467.g002 PLOS ONE Climate and vegetation trends in the Pearl River Delta PLOS ONE | https://doi.org/10.1371/journal.pone.0245467 February 24, 2021 7 / 20