Reliability of urban microclimate simulations: spatio-temporal validation through intra-urban canyon transects for outdoor thermal comfort analysis

Mitigating Urban Heat Island (UHI) intensity in cities through adaptative strategies has become an urgent need, as UHI are also exacerbated by climate change impacts imputable to anthropogenic actions. This study addresses the need for reliable simulation models to analyze outdoor thermal comfort (OTC) in future or alternative scenarios. The aim of the present study is to contribute to the validation of CFD urban microclimate simulations by employing intra-urban canyon transects as an alternative or a complementary approach to fixed stations. To accomplish this, we developed a cost-effective monitoring unit to carry out transects on a pre-defined route (1), devised the area of interest (2), elaborated a simulation model in ENVI-met (3), and proposed different validation methods for comparative analyses (4). Results indicate that temporal validated simulation tended to underestimate thermal indices in the morning and night and overestimate them in the afternoon, while spatio-temporal validation under a human-centric comfort approach via wearable sensing notably improved accuracy. Moderate to very strong agreement between simulation and measurement data in summer (Willmot's d similar to 0.70, d similar to 0.81) and very strong agreement in winter (d similar to 0.79, d similar to 0.96), with low error magnitudes in summer (RMSE similar to 0.91 degrees C and 9.59%, MBE similar to 0.23 degrees C and 9.10%) have been found. In winter, such figures were RMSE similar to 0.71 degrees C and 3.51%, MBE similar to 0.00 degrees C and 0.98%, for the spatio-temporal validated model. This research contributes to enhancing the reliability of relatively affordable CFD urban microclimate simulations, supporting its scale up for policymakers in implementing effective strategies for OTC.