Contemporary Urban Expansion in China and its diverse effects

The scale of urbanization in China during the past 30 years is unprecedented in human history along with its fast economic growth, presenting profound impacts on socioeconomics, human well-being, and the environment. We quantified spatial patterns and temporal courses of urban land expansion for 32 major cities across China from the late 1970s to 2010 using multitemporal Landsat data of 1978, 1990, 1995, 2000, 2005, and 2010, and further explored the effects of urbanization on climate (i.e., urban heat islands), and vegetation phenology and growth in these 32 cities, together with MODIS Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI) products.

We found that rapid urban expansion was observed in these 32 major cities from 1978 to 2010, with an overall annual expansion rate of 6.8 ± 2.5 %. Chinese urban expansion does not fit urban expansion theory consistently over time and has transitioned from contradicting to conforming to Gibrat’s law, which states that the growth rate is independent of city size. The surface urban heat island intensity (SUHII) differed substantially between day and night and varied greatly with season. Spatial variability of the SUHII is ultimately controlled by background climate. The growing season started 11.9 days earlier and ended 5.4 days later in urban zones compared to rural counterparts. The phenological sensitivity to temperature were 9-11 days SOS advance and 6-10 days EOS delay per 1 °C increase of LST. For the first time, we developed a general conceptual framework for quantifying the impacts of urbanization on vegetation growth and applied it in 32 Chinese cities. Results indicated prevalent vegetation growth enhancement in urban environment and vegetation growth was enhanced at 85% of the places along the intensity gradient. This growth enhancement offset about 40% of direct loss of vegetation productivity caused by replacing productive vegetated surfaces with non-productive impervious surfaces. The urban environments, considered as the "harbingers" of global environmental change and "natural laboratories" for global change studies, shed new insights and approaches into global change science, and the urban-rural gradient provides an excellent experimental manipulations for global change studies.