Analysis of Diurnal and Nocturnal Vertical Profiles of Air Temperature in an Urban Canyon – A Tropical Campus Case Study
Authors:
May Lwin Oo (1), Nyuk Hien Wong (1), Shanshan Tong (1), Jun Chung Daniel Hii (2), Erna Tan (1), Joie Lim (1), Marcel Ignatius (1)
(1) Department of Built Environment, National University of Singapore, Singapore.
(2) KAJIMA Technical Research Institute Singapore
Abstract:
Urban geometry and surface properties strongly affect diurnal and nocturnal air-temperature variations in urban canyons. This study examines vertical air temperature profiles in a southeast-northwest (SE–NW) oriented urban canyon (H/W = 2.5, SVF = 0.2) located on the tropical campus of the National University of Singapore using field measurements and Computational Fluid Dynamics (CFD) simulations. Seven weather stations, a meteorological tower, and an infrared thermal camera were used for model input and validation, while air temperature, surface temperature, and radiative heat flux were simulated at 10 AM and 2 PM during the daytime and at 10 PM, 12 AM, 4 AM, and 6 AM during the night and early morning. The results show that daytime air temperature increases with height due to solar heating of façades and ground surfaces under strong buoyant mixing. At night, the profiles evolve toward a stable negative vertical gradient under weakly convective conditions dominated by longwave radiative cooling, reflecting greater heat trapping in the lower canyon and more efficient cooling toward the open atmosphere above. Radiative cooling weakens around 4 AM and approaches near-zero net loss by 6 AM as surfaces reach thermal equilibrium. These findings elucidate heat trapping and release mechanisms in tropical high-density canyons and inform strategies for reducing outdoor heat stress.
Keywords:
Vertical profiles of diurnal and nocturnal air temperature, urban canyon, surface properties, shortwave and longwave radiation.