<p>Urban Heat Islands (UHIs) are a critical concern in urban environments due to their impact on local climates and human health. Characterized by elevated temperatures in urban areas compared to rural surroundings, UHIs are primarily caused by extensive urbanization and resulting land cover changes. Research on the UHI phenomenon has been limited in South Bihar. This study examines UHI intensity in four urban areas in South Bihar, India—Patna, Gaya, Nawada, and Biharsharif—as representative samples of different urban regions in the area, from 1990 to 2023. These areas have been experiencing rapid urban growth, making it crucial to understand the long-term changes in UHI intensity, their underlying causes, and associated land degradation. The primary objective of this study is to investigate changes in UHI intensity and their relationship with land cover alterations over the past three decades in South Bihar. The study utilizes Google Earth Engine for processing satellite data. Land Surface Temperature (LST) was derived from Landsat thermal bands, and a Random Forest (RF) classifier was employed for land cover classification using data from Landsat-5 and Landsat-8. The RF classifier was chosen for its robustness and accuracy in handling high-dimensional data. The results indicate significant land cover changes across the studied urban areas. Built-up areas have markedly increased in all study locations, largely at the expense of vegetation and bare land. For instance, in Patna, built-up areas grew from 40.40 km² in 1990 to 62.19 km² in 2023, while vegetation cover decreased from 42.47 to 17.62 km². Similar trends were observed in the other cities. These changes not only intensify the UHI effect due to greater heat absorption and retention but also contribute to land degradation, including soil erosion, loss of fertile land, and diminished ecosystem services. The reduction in vegetation, which provides natural cooling through evapotranspiration, exacerbates UHI effects while accelerating land degradation processes. Furthermore, the replacement of permeable surfaces with impermeable ones leads to increased surface runoff and decreased groundwater recharge, adding to environmental challenges. The study’s findings highlight a strong association between expanding built-up areas, higher UHI intensities, and worsening land degradation. This underscores the need for sustainable urban planning that incorporates green infrastructure and strategies to minimize land degradation. Measures such as enhancing urban vegetation, promoting permeable urban surfaces, and implementing land-use policies that prioritize ecosystem health are vital to mitigating the adverse effects of UHI and preserving the environment in South Bihar.</p>