Nonlinear and Seasonally Heterogeneous Responses of Land Surface Temperature to Land Use and Urban Functional Zone: A Case Study of Xi'an, China

Abstract

Urban heat island (UHI) effects increasingly threaten sustainable urban development under the combined pressures of climate change and rapid urbanization. Nevertheless, most existing studies focus on single seasons or extreme summer events, with limited attention to the nonlinear and seasonally heterogeneous relationships between land surface temperature (LST), land use, and urban functional zones, particularly in cold-region cities. To address this gap, this study investigates the monthly and seasonal dynamics of the urban thermal environment in Xi'an, a rapidly urbanizing city in northwestern China characterized by cold winters and pronounced summer heat risk. Multisource datasets, including Landsat 8 thermal imagery, Points of Interest, and OpenStreetMap road networks, were integrated to delineate urban functional zones and surface characteristics. LST retrieval, spectral unmixing, kernel density estimation, and polynomial regression were employed to quantify both linear and nonlinear associations between surface composition, functional zoning and LST. Results reveal pronounced seasonal heterogeneity in LST patterns, with mean LST ranging from approximately 1 °C in winter to over 41 °C in early summer. UHI intensity peaks in summer (up to 6.45 °C) and weakens substantially in winter. Impervious surfaces exhibit a consistently positive relationship with LST across seasons, with the strongest linear association observed in summer (r = 0.77). Vegetation exerts significant cooling during the growing season, particularly in summer (r = −0.56), but this effect diminishes in winter and becomes marginally positive. Nonlinear analyses further identify threshold behaviors in built-up and bare soil surfaces, beyond which warming accelerates, particularly in autumn and winter, whereas water bodies show comparatively limited regulatory effects. These findings clarify the seasonal and nonlinear mechanisms linking LST with land use and urban functional structures in cold-region cities and provide scientific support for seasonally adaptive and function-oriented urban heat mitigation strategies.