Field measurement and CFD simulation study on UHI in high-density blocks of Shanghai based on street canyons

The impact of urban heat island (UHI) on urban environments and residents has worsened, especially at the block-scale, drawing significant research attention to thermal issues. This study analyzes typical Shanghai blocks through field measurements and simulations. First, 12-day field measurements in summer and winter captured UHI spatiotemporal distribution. The average urban heat island intensity (UHII) was 3.19 °C in summer (daytime 2.25 °C, nighttime 4.13 °C) and 1.93 °C in winter (daytime 1.54 °C, nighttime 2.33 °C). The maximum temperature difference between points reached 10.8 °C in summer and 4.09 °C in winter, with greater temperature fluctuations in single-functional blocks than in multifunctional ones. Then, based on simulations, linear and curve fitting equations for UHII with changes in solar radiation intensity (SRI) or wind speed showed accurate results. For the linear fitting, a ± 10 % change in SRI or wind speed resulted in a ± 0.26 °C or ∓0.16 °C change in summer UHII, and a ± 0.14 °C or ∓0.10 °C in winter UHII. Quantitative analysis of wind direction changes showed that high-density areas downwind of green spaces or waterfronts saw summer UHII drop by up to 91.61 %. Multiple regression analysis of street canyon node temperatures showed good fits for six blocks. This study provides theoretical support and references for UHI mitigation and block-scale planning.