Long-term tracking of urban structure and analysis of its impact on urban heat stress: a case study of Xi’an, China

Rapid urbanization has rapidly transformed the urban thermal environment, significantly impacting the daily lives of urban residents and socio-economic activities. Therefore, analyzing the long-term changes in urban structure and the urban thermal environment is of great importance. This study utilizes the Google Earth Engine (GEE) platform and remote sensing tools, employing Landsat and Sentinel series satellite imagery, and introduces the LCZ classification system to identify and study the dynamic changes in the urban structure of Xi’an City and its central Yanta District in 2009, 2014, 2019, and 2023. The WRF-SLUCM model is used to conduct mesoscale climate simulations for the central area of Xi’an, with WBGT as the thermal stress indicator. Pearson correlation analysis is employed to explore the long-term relationship between the thermal environment and urban structure in the study area.The results show that from 2009 to 2023, the area of built-up land types in Xi’an rapidly increased. The expansion trend is characterized by the rapid spread of LCZ4 to the northern and southern parts of the city, accompanied by a large-scale reduction of LCZ6. The shape and area of the high-temperature zones in Yanta District did not change significantly. However, from 2009 to 2023, the proportion of open high-rise, open mid-rise, and dispersed buildings in Yanta District continued to increase, while the proportion of compact high-rise, compact mid-rise, single-layer dense buildings, and heavy industrial buildings continued to decrease. This indicates a trend of increasing height and decreasing density in the urban structure of the central area of Xi’an over time. Numerical simulation results show that over time, temperature, wind speed, and WBGT in Yanta District exhibited a downward trend, while humidity increased. The average daily temperature decreased by 0.35 °C, average humidity increased by 0.34 g/kg, average wind speed decreased by 0.36 m/s, and average WBGT decreased by 0.25 °C. Correlation analysis results indicate that LCZ7, LCZ8, LCZ10, and LCZE are significantly positively correlated with urban heat stress, while LCZA, LCZD, and LCZG are significantly negatively correlated with WBGT. LCZ8, LCZ10, LCZA, and LCZG have the most significant impact on WBGT, with correlation coefficients of 0.61, 0.44, −0.46, and −0.50, respectively. In future urban planning and development, increasing building height, reducing building density, and decreasing impervious surfaces can improve the comfort and safety of the urban climate. The findings of this study can provide reference for future urban planning and promote the sustainable development of Xi’an.