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Climate change adaptation in urban areas is among the biggest challenges humanity faces partly because of the combined effects of urban heating and global warming. The variability of urban heat islands (VUHIs) is known to influence the effectiveness of climate adaptation strategies; however, the understanding of VUHIs is still limited. Here, we quantified the diurnal and seasonal VUHIs in 245 Chinese cities that varied in population and physical size based on the remotely sensing data from 2002 to 2012. Taking the 2012 VUHIs as an example, we examined the relationships between VUHIs and underlying drivers of background climate and urbanization. The results showed that: (1) the VUHIs from 2002 to 2012 had obvious periodicity in different years while significant diurnal and seasonal variability; (2) the explanation rates of local background climate for the diurnal VUHIs were 30% (spring), 19% (summer), 29% (autumn), and 25% (winter), respectively; (3) the explanation rates of urbanization for the diurnal VUHIs were 13% (spring), 22% (summer), 11% (autumn), and 21% (winter), respectively; (4) these two variables also accounted for 32% and 12% of the seasonal VUHIs during the daytime, and 25% and 23% during the nighttime, respectively. Our research suggests that the improvement of urban climate-change adaptation necessitates local "climate-smart" strategies, a reduction in local anthropogenic heat emissions, and rational use of green planning for sustainable urban development. (C) 2018 Elsevier Ltd. All rights reserved.