Quantify the shading effects on alleviating human thermal stress across different local climate zones in the Yangtze River Delta

Abstract

Shading has been widely recognized as an effective strategy for ameliorating human heat stress. The shading effect varies across different urban microclimates, influenced by urban morphology. However, existing research on evaluating shading effects mainly focuses on point-based observations or block-scale simulations, resulting in limited regional representation. To address the gaps in regional-scale evaluations, we quantify the improvement of human heat stress (measured by Universal Thermal Climate Index, UTCI) in shaded areas of the Yangtze River Delta (YRD) by considering/not considering solar radiation when calculating the UTCI. The method primarily relies on accurate descriptions of the urban microclimate. Therefore, the Weather Research and Forecasting (WRF) model, incorporating local climate zones (LCZs) land use data, is used to simulate the thermal environment during the summers of 2020 and 2022 in YRD. The results indicate that the daytime average outdoor UTCI in compact high-rise building (LCZ1) is 38.19 °C, with 53 % of the time experiencing “very strong heat stress”, which is higher than sparsely built (LCZ9). After shading, the urban demonstrates a more effective shading effect than rural. The UTCI decreases by an average of 5.18 °C across the LCZs, with the most effective shading generally occurred at 1000LST. Furthermore, the shading effect is more significant under high-temperature and moderate-humidity conditions, whereas excessively high or low humidity diminish shading effects. Our research bridges the scale gaps in shading effect evaluations, and can provide more comprehensive guidance in improving the urban environment.