Spatio-temporal evolution of surface urban heat islands in the Chang-Zhu-Tan urban agglomeration

Abstract

Urban agglomeration has become increasingly important over recent decades; however, little is known about the spatiotemporal patterns and evolution of the surface urban heat islands (SUHI) that have arisen in urban areas. The objective of this study was to monitor the spatiotemporal patterns of such SUHI in the urban agglomeration using dense Landsat time series. Landsat images were collected in the Changsha-Zhuzhou-Xiangtan (CZT) region from 2000 to 2017. The land surface temperatures were calculated using the Google Earth Engine and investigation of SUHI phenomenon. The Mann Kendall test (M-K), Theil Sen Median trend analysis (Sen), Standard Deviational Ellipse, and mean center analysis were applied to analyze the spatio-temporal patterns of SUHI. Results indicated that: 1) SUHI was always more obvious in summer than in the three other seasons. Additionally, the SUHI was always higher in Zhuzhou than in Changsha or Xiangtan. 2) The mean center of the SUHI in the three cities has begun to converge, together with the connectivity of SUHI in the CZT urban agglomeration, which is also gradually increasing. 3) There are spatial disparities in the changes to SUHI. The SUHI in the areas surrounding urbanization and the urban core is increasing and decreasing, respectively. The change in the direction of the increase in the SUHI of the three cities shows movement towards the core of the neighboring city. 4) The main reason for causing this variation is the change of landcover type. 77.103% of all the pixels with an obvious growing SUHI trend has changed to impervious areas. The active factory may influence the changed pattern of SUHI. This study suggests that the SUHI in the urban agglomeration is undergoing aggregation, together with the increasing variation in the urban agglomeration.