Simulating the daytime and nighttime urban heat island effect on neighbourhood scale

This study aims to characterise and understand the magnitude of the urban heat island effect for an urban geometry at neighbourhood scale. For this purpose, a simulation program has been developed which combines radiative transfer by a Monte Carlo model, conductive heat transport by the 1D heat conduction equation and convective heat transport by computational fluid dynamics (CFD) modelling at 1 meter resolution. This model can be used to provide more insight in the mechanisms underlying the urban heat island effect.

For this study, summer conditions (day and night time) are considered in an idealised 2D urban geometry, where a range of height (H) to width (W) ratios (0.0 (flat plate), 0.5, 1.0, 2.0 and 4.0) is considered. Starting with a radiation only case, complexity is added with each next test case, adding the long wave trapping process, ground heat flux process, sensible heat flux process and finally an anthropogenic heat of 50 W/m2. With this set of simulations, a clear indication can be given on the most important mechanisms controlling the urban air temperature.