## 4 Discussion  
This study aimed to investigate the UHI effect in Zhengzhou over the past decade (2012-2021). The results showed that the UHI effect has increased in the city's urban areas compared to the rural areas. This increase can be attributed to the rapid pace of urbanization that has taken place in Zhengzhou and around the world. Urbanization has led to the construction of more buildings and roads, which absorb and store heat from the sun during the day and release it at night, contributing to higher temperatures in urban areas. In addition, the increase in the population and energy consumption in urban areas generates more heat, exacerbating the UHI effect. The UHI effect significantly impacts human health and the environment, including increased energy consumption for air conditioning, higher air pollution levels, and heat-related illnesses. Therefore, it is essential to understand and mitigate the UHI effect in urban areas through strategies such as green roofs, tree planting, and urban design that promotes natural cooling and reduces the amount of heat absorbed and stored by urban surfaces. Currently, the rate of urbanization around the globe is accelerating [3]. Rapid urbanization has been a critical driver of economic prosperity and social advancement but has also negatively affected the global environment [36]. The UHI effect has emerged as a significant concern among the ecological impacts attributed to urbanization. The intensification of UHI in urban areas can have far-reaching consequences on the climate, human health, and ecosystems. Hence, it is imperative to mitigate the UHI effect through appropriate urban planning and design measures and adopt sustainable development strategies [37; 38]. As the area of urban construction increases, many natural surfaces are transformed into impermeable surfaces. Urban regions absorb more heat than suburban areas because built-up areas decrease the evaporation capacity of a city, and the emissions of buildings cannot evaporate as quickly as those of urban vegetation and  
Figure 14: Statistical analysis of seasonal LST of different land types in Zhengzhou in (**a**) 2012 and (**b**) 2020.  
water bodies, which also raises the city's temperature [39]. As a result, the urban surface temperature is higher than that of other land types. The built-up area of Zhengzhou City is increasing year by year, and the surface temperature of the built-up area is also gradually rising, which leads to an increase in the intensity of the UHI. Due to the rapid urbanization and industrialization of human civilization, UHI is one of the significant problems of the 21 st century [40; 41; 42]. To measure the effect of UHI, UHI is used. Previous studies show that researchers have used different metrics to measure UHI. However, limited studies have been carried out to analyze the UHI effect in Zhengzhou. In this study, using a combination of MODIS products and 3S technology, the UHI and LHII in Zhengzhou from 2012 to 2021 have been studied and analyzed to evaluate the thermal environment impact of different areas of Zhengzhou. In 2021, moderate heat islands were distributed in the central part of the city; however, weak heat islands were present in other parts of the urban areas (Figure 4). According to the distribution of the daytime and nighttime LST in Zhengzhou in 2021, the highest temperature and UHI in the day and night are 35 \({}^{\circ}\)C and 0.87 \({}^{\circ}\)C and 24.5 \({}^{\circ}\)C and 1.7 \({}^{\circ}\)C, respectively, as shown in Figure 5. Initially, it was hypothesized that the winter urban heat island effect in Zhengzhou is primarily caused by the concentrated urban heating supply when comparing urban and suburban areas. The prevalence of heating pipes and indoor heating contributes to higher temperatures in urban regions, thereby leading to a more pronounced winter heat island effect, particularly during the nighttime (Figures 5 and 10). The thermal properties of Zhengzhou and daytime and nighttime variations during different seasons are shown in Figures 7 and 8.