Comparison of Urban Heat Island Differences in the Yangtze River Delta Urban Agglomerations Based on Different Urban–Rural Dichotomies.

The surface urban heat island (SUHI) phenomenon has become increasingly severe due to the combined effects of global warming and rapid urban expansion, and the difference between urban and rural thermal environments has increased significantly. This trend has profound impacts on social, economic, and ecological environments. Research related to SUHI has achieved fruitful results; however, quantitative research methods for SUHI have not been unified with standards and systems, which will certainly affect the comparability of the results of SUHI research. Few studies have combined and compared multiple SUHI methods. Therefore, we designed a study of the Yangtze River Delta (YRD) urban agglomeration as a test case to quantitatively analyze the differences between SUHI results in different urban and rural contexts based on five different SUHI research methods. It was found that (1) there were significant differences in the SUHI intensity results among the different methods. The maximum difference in the SUHI intensity obtained by different methods can be up to 6 °C. The lowest SUHI intensity was observed during the day in the urban–buffer method, and the lowest SUHI intensity was observed at night in the urban–water method. (2) Different methods affected the distribution of SUHI areas and their evolutionary characteristics. The NHI (no heat island), WCI (weak cold island), and WHI (weak heat island) zones were larger, with proportions exceeding 70%. The expansion range of the heat island zone during the daytime was mainly in the west and north of the YRD urban agglomeration, whereas the expansion of the heat island range at night was mainly concentrated in the center and south. (3) The trend changes observed using different methods were significantly different. When we applied the urban–buffer and municipal–nonmunicipal methods, most cities showed an upward trend. However, when the other methods were applied, most cities exhibited a downward trend. The differences in trend results owing to the choice of different methods were greater with respect to values in the summer months and smaller in the winter months. [ABSTRACT FROM AUTHOR]