Analysis of urban thermal structures in different scenarios of hot weather: The Bologna case study

It is recognized that in summer many urban areas increasingly experience days of extreme heat caused by a combination of regional climate change and local effects due to the Urban Heat Island (UHI). Southern Europe, particularly the Po Valley region in Italy, faces several challenges such as land degradation, rapid urbanization, and intensifying climate impacts, with Bologna exemplifying the intricate interplay between these risk factors. Here, high-resolution Weather Research and Forecasting (WRF) model simulations are employed to investigate the three-dimensional urban thermal dynamics under present and future projected extreme heat scenarios. A multi-scale modeling framework is applied to simulate representative Hot Weather (HW) events in the near and far future under two emission scenarios (SSP245 and SSP585), along with a present-day reference event. Results show that the UHI effect persists in all cases and intensifies during HW periods, especially at night. HW events induce strong near-surface warming, with a persistent urban–rural temperature contrast of about 3–5 °C and an upward shift of the 30 °C isotherm, while simultaneously compressing the UHI vertically from ∼ 250 m in present conditions to ∼ 100–140 m in future HW scenarios. Scenario-dependent differences emerge, especially in the far future: SSP585 leads to stronger and more persistent nocturnal overheating, slower recovery, and deeper atmospheric warming, whereas SSP245 shows more moderate, rapidly reversible UHI anomalies with a more regular diurnal cycle. This study highlights the importance of a three-dimensional diagnostic approach and underscores the role of emission pathways in modulating future urban heat stress. • The Urban Heat Island in Bologna is studied under present and future climate scenarios. • High-resolution simulations capture horizontal and vertical urban thermal structures. • Hot weather events reduce the vertical extent of Urban Heat Island effect by ∼ 100 m. • Future high-emission scenarios predict warmer nights, persisting up to 4–5 days after hot weather events. • Future low-emission scenarios show limited hot weather days and faster post-event cooling.