Distinctive roles of two- and three-dimensional urban structures in surface urban heat islands over the conterminous United States

In this study, we investigated how seasonal and diurnal surface urban heat islands (SUHIs) vary with two- and three-dimensional (2D and 3D) urban structure parameters (USPs) and climate settings. Additionally, whether and how 2D and 3D USPs influenced the seasonal hysteresis between SUHIs and background temperatures were explored using remote sensing for 203 cities over the conterminous US. Results show that urban areas with high impervious surface coverage (70%) were "colder" in summer than surrounding rural areas in dry climates. Moreover, the cooling efficiency of vegetation in dry climates was about two times higher than that in wet climates. A hump-shaped relation between sky view factor (SVF) and SUHIs was observed; in regions with low SVF (e.g., SVF < 0.4), the increasing trends of summer diurnal SUHIs with increasing SVF in dry climates attained higher values than those in wet climates. Seasonal hysteresis between background temperatures and SUHIs was largely controlled by 2D and 3D USPs. Urban USPs and climate settings can regulate the timing of peaks and nadirs of annual SUHIs, suggesting that their regulation would benefit SUHI mitigation. Future studies are required to test USP-LST relationships further by using the local climate zone approach under different climatic conditions.