Exploring Urban Heat Islands with a simple thermodynamic model

The Urban Heat Island (UHI) effect, characterized by elevated urban temperatures compared to rural areas, is a critical challenge in urban climatology, exacerbated by global warming and rapid urbanization. This study investigates the fundamental mechanisms of the UHI effect by integrating theoretical modeling with observational data from Korea, focusing on the interplay between urban heat storage, anthropogenic heat, and climatic factors. Using a simplified day-night model based on the Surface Energy Flux Balance (SEFB) framework, we demonstrate that the UHI effect arises primarily from two mechanisms: (1) a decrease in the diurnal temperature range (DTR) due to the increased heat capacity of urban materials, and (2) an increase in mean temperature driven by additional energy fluxes, such as anthropogenic heat. Comparative analysis between Seoul, a major city, and Boeun, a rural area, reveals qualitative agreement between model predictions and observed data. Despite its higher latitude, Seoul exhibits significantly higher nighttime temperatures than Boeun, underscoring the role of urban heat storage in sustaining nighttime warming. Additionally, a temporary daytime temperature inversion in Boeun, driven by greater solar radiation, highlights the contrasting thermal dynamics between urban and rural environments. Long-term analyses reveal distinct evolutionary patterns of UHI effects in major cities and new towns. In major cities, rapid urbanization from the 1970s to the 1990s led to a steady decrease in DTR and a peak in nighttime temperature differences, followed by stabilization. In contrast, new towns consistently increased nighttime temperature differences, closely tied to urban development and population growth. Both cases demonstrate the critical role of heat storage and anthropogenic heat in shaping the UHI effect, with observed trends closely mirroring theoretical predictions. This study emphasizes the vulnerability of urban areas to climate change, as UHI effects amplify global warming's impact, heightening urban heat stress.