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. China differs from either developed or other developing countries in its urbanization process, and the characteristics and consequences of urbanization in China calls for more in-depth studies at the national level and more theoretical understanding. 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, 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 LST and EVI products.
Results/Conclusions
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%. Our patch analysis revealed a converged urban patch structure as the number of patches for a given patch size in any city can be predicted by a unified function of the patch size and the total urban area. 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.