Validation of CFD in Simulating Urban Water’s Cooling Effect in Subtropical Climate Area

Abstract

To assess the microclimatic impacts of UHI mitigation design during the urban planning stage, researchers often utilize Computational Fluid Dynamics (CFD) models such as ENVI-met. ENVI-met is a three-dimensional, non-hydrostatic microclimate model based on the principles of fluid dynamics and thermodynamics. It simulates the exchange processes among urban surfaces, vegetation, air, and built structures. These components operate within an integrated model that allows for the spatially and temporally resolved simulation of urban environments. With these capabilities, ENVI-met had been adapted to urban microclimate studies and climate-sensitive design. Before simulation results can be applied to real-world planning, model validation is essential to determine whether the outputs accurately reflect observed environmental conditions. However, existing studies offer limited validation of ENVI-met’s ability to simulate the seasonal cooling effects of urban water bodies, especially in subtropical climate contexts.

In this study, our objective is to evaluate ENVI-met’s ability in simulate the seasoning cooling effects of urban water bodies. By comparing model outputs with on-site measurements collected near water features in a subtropical city-Taipei, we aim to know the difference between simulation and reality. Field data including air temperature, relative humidity, specific humidity and MRT, were used for comparison. Preliminary results show strong agreement between simulation and measurement: air temperature RMSE ranged from 0.16 to 0.23°C with R² values of 0.94–0.97, while relative humidity MAPE ranged from 2.90% to 3.45%, with R² values of 0.76–0.91. These findings confirm that ENVI-met can reliably simulate water-induced cooling effects in urban environments.