Assessing Urban Microclimate Modelling Variability: A Comparative Analysis Of ENVI-met And SLUCM Across Multiple LCZs In Hong Kong

This study presents a comparison of two leading urban climate models - the Single Layer Urban Canopy Model (SLUCM) and ENVI-met - across six Local Climate Zones (LCZs) in Hong Kong. While previous validations have focused primarily on individual LCZ types, this research evaluates model performance across diverse urban morphologies, incorporating seasonal variations and vegetation effects. The study analyzed model performance using high-resolution pedestrian-level observational data.

Both models demonstrated comparable accuracy in simulating air temperature (Ta) and relative humidity (RH), with SLUCM showing slightly superior performance. The largest Ta prediction errors were observed in the most and least dense LCZ types, while the presence of vegetation increased RH prediction errors. The impact of SLUCM's Building Energy Model (BEM) had a significant impact on summer simulations, particularly affecting waste heat predictions and thermal comfort calculations.

Seasonal analysis revealed an average Ta decrease of 11.94°C and RH reduction of 7.94% between summer and winter conditions across sites. All studied locations exhibited strong heat stress according to both Universal Thermal Climate Index (UTCI) and Physiological Equivalent Temperature (PET) metrics during summer months, with the compact high-rise zone (LCZ 1) showing the highest thermal stress levels. This suggests the need for city-wide heat mitigation strategies rather than targeted localized interventions.

The research highlights how methodological choices in urban climate modeling influence the interpretation of results. While ENVI-met's computational fluid dynamics (CFD) approach produced warmer, more homogeneous conditions due to resolved flow fields, SLUCM's surface energy balance method resulted in cooler, more stratified conditions owing to its simplified treatment of turbulent mixing. The study recommends incorporating HVAC calculations into ENVI-met simulations and using both PET and UTCI indices for a more balanced assessment of thermal comfort conditions.

These findings contribute to our understanding of urban microclimate modeling capabilities and limitations, providing valuable insights for researchers and urban planners in subtropical climates. The research emphasizes the importance of considering model selection, seasonal variations, and multiple thermal comfort indices in urban climate analysis and design decision-making.