Reconciling Debates in Controls of Urban Heat Islands: the Effect of Scaling and Sampling

Abstract:

One of the most profound modification of climate induced by the urbanization is the surface urban heat island (SUHI), a phenomenon of the significantly higher surface temperatures in urban areas referenced to the surrounding rural lands. It has been commonly believed that variations of SUHIs can be explained by factors related to surface status, climate (or weather) conditions, and urban development intensity. Disagreements however appear on the relevant importance of these three types of factors. Here we conduct a systematic investigation on the SUHI controls across 800-plus Chinese cities to attribute such disagreements to the impact of scale and sampling. We find that with an increase in temporal scale, the contributions from climate (or weather) conditions gradually decrease, whereas those from surface status and development intensity increase. Common ranks of these three types of factors can only be summarized for the SUHI spatial variations over a regional/continental scale, not for those among neighborhood cities. Disagreements may also be induced by sampling style: different ranks of SUHI controls may appear if identified among different city cluster samples (e.g., city cluster samples with different urban areas or within different climate zones) or over different time periods (e.g., in summer or winter time). Our study has potential to advance a better literature communication on the SUHI mechanisms as well as a more accurate understanding of this phenomenon.