Exploring Nanjing’s Urban Heat Island through Surface Energy Budget Analysis

Urbanization drives economic growth and improves living standards but also brings challenges, such as increased energy consumption, air pollution, and climate changes. A key issue is the Urban Heat Island effect, where urban areas experience higher temperatures, greater heat retention, and altered energy flux patterns compared to vegetation-rich rural regions.These changes not only exacerbate local heating but also disrupt natural ecosystems and water cycles.This study explores the urban heat island effect by analyzing differences in surface energy budgets between urban, grassland, and cropland sites in Nanjing, China. Data collected from May to September 2013 include variables such as air temperature, four-component radiation, and energy fluxes. The results reveal that urban areas for most of the time exhibit higher nighttime temperatures due to increased heat release by impervious surfaces. In contrast, rural sites, particularly in cropland, demonstrate effective cooling mechanisms through higher latent heat flux driven by evapotranspiration. Grassland temperatures fall between the other two site types, reflecting moderate cooling effects. In general, urban areas show a higher proportion of energy being converted into sensible and ground heat flux. In contrast, rural areas allocate more energy to latent heat flux. This study highlights the need to integrate vegetation into urban planning to reduce heat and improve thermal comfort.