Spatial-temporal variations of surface urban heat island intensity induced by different definitions of rural extents in China

Surface urban heat island intensity (SUHII) widely acknowledged as the primary indicator has been extensively utilized in previous SUHI spatiotemporal research. However, diverse rural definitions reported in previous studies possibly affect rural temperature and consequently lead uncertainty and incomparability to SUHII dynamics. Despite of previous efforts, there are still some issues in systematic analysis of significance and spatiotemporal variations of SUHII interpretations resulting from these different rural extents. In order to address these issues, this paper quantitvely characterized the significance and spatiotemporal dynamics of RE-induced Delta SUHII (Rural-extent induced SUHII variations) in 100 major cities across China mainland. Major findings are summarized in the following three aspects. First, considerable SUHII variating with rural buffers extending and majority of Delta SUHII exceeding 0.5 K especially in the daytime illustrated that different rural definitions can induce significant uncertainty to SUHII studies. Second, RE-induced Delta SUHII is found to be unevenly distributed across the study area. Moreover, dense distributions of great Delta SUHII in city agglomerations suggest that city is an inappropriate study object for SUHII urban-cluster research since multi-influences from aggregated urban and rural areas without clear boundaries. Third, RE-induced Delta SUHII experiences evident seasonal variations especially in the daytime spring and summer, and spoon-shape (peaks in the begins and ends, and bottom in the middle) buffer variations with relatively low correlations among five subdivided buffer rings. Additionally, six potential factors are selected to discuss their possible effects on Delta SUHII spatiotemporal characters. On the whole, this paper illustrated that diverse rural extents do induce conspicuous uncertainty and incomparability to SUHII interpretations and highlight the necessity to develop uniform rural defining standards in the future SUHII research. (C) 2019 Elsevier B.V. All rights reserved.