Fine-Scale Spatiotemporal Analysis of Urban Heat Island Dynamics in the Central Yunnan City Cluster

Abstract With the acceleration of urbanization, the construction and population density of cities have continuously increased, leading to a more pronounced urban heat island (UHI) effect. This phenomenon has significant impacts on urban ecological environments and human health, including elevated temperatures, reduced water resources, decreased visibility, and deterioration of ecological conditions. It is imperative to mitigate Urban Heat Island effects (UHIs) and improve ecological conditions. Previous studies on UHIs have primarily focused on large cities, and it remains unclear whether UHIs exist in small-scale cities and how their spatiotemporal patterns evolve. This article conducts a detailed study of the spatiotemporal variations of Surface Urban Heat Island Intensity (SUHI) in the Central Yunnan City Cluster from 2000 to 2021 using Landsat satellite data, completing the time series of Urban Heat Island Intensity index (SUHII) for 44 cities at the county level. The study quantitatively estimates the overall SUHI trend and explores driving factors, yielding the following conclusions: Small cities also exhibit UHIs, irrespective of city size. From 2000 to 2021, the probability of UHIs occurrence in the Central Yunnan City Cluster was 75.4%, resulting in an overall reduction of 1.21°C in surface urban heat island (SUHI) intensity; The severity of Urban Heat Island effects increases with larger defined suburban areas, accompanied by a faster rate of change; The method of fitting SUHII trends for all cities allows for a robust quantitative estimation of the overall SUHII trend in the Central Yunnan City Cluster, achieving a high coefficient of determination (R²) value of 0.95; Human activities and land use changes influence the formation of decreasing SUHII trends; Urban expansion areas experience the highest temperature growth rate, while the city centers show the slowest growth rate, contributing to the formation of decreasing SUHII trends. This research highlights the presence of UHIs even in small cities, providing insights for enhancing ecological conditions.