Urban Heat Island Effect in Different Sizes from a 3D Perspective: A Case Study in the Beijing–Tianjin–Hebei Region

In the Beijing–Tianjin–Hebei urban agglomeration—one of China’s three largest city clusters, the GDP reached CNY 950 billion with a population of approximately 110 million in 2021. While megacity expansion has slowed, rapid growth in small and medium-sized cities is expected to increase their vulnerability to urban heat island (UHI) effects. This necessitates urgent, size-differentiated studies of the UHI to inform sustainable urban planning. This study examines the Beijing–Tianjin–Hebei urban agglomeration using Landsat 8 data to explore the UHI between different-sized cities and analyze the driving mechanisms of UHI intensity attributed to urban buildings. The results indicate the following: (1) Beijing displays the smallest temperature change (1.39 °C) and lower heating effect intensity (484.44 km2 °C) compared to Shijiazhuang (919.11 km2 °C); (2) a logarithmic relationship (R2 = 0.4261) exists between the building volume and heating effect intensity, and the specificity of megacities significantly influences the regional analysis results of the heat island effect; and (3) the total energy consumption power of the heating effect in 10 cities within the Beijing–Tianjin–Hebei region is 326.23 × 1012 KJ/h, which is equivalent to 11.14 × 109 kg/h of standard coal.