Impact of urban albedo on microclimate:Computational investigation in London

The urban albedo (UA), defined as the ratio of the reflected to the incoming shortwave radiation at

the upper edge of urban canyons, quantifies their ability to reflect solar radiation towards the sky. This research

investigates the impact of real-world urban geometries and optical properties of facades and roads materials on

the UA and street level microclimate in London. The Indexed Sphere (IVS) algorithm of ENVI-met 4.4.4 is used to

compute the UA of several canyon configurations. The accuracy of the IVS algorithm is evaluated against

measurements on a 1:10 physical model reproducing the geometry and materials of the case study area. The

simulation results show that reflective materials applied to the canyon surfaces are more effective in increasing

the UA of canyons with low aspect ratios. The use of reflective materials in urban canyons always increases the

amount of reflections at the street level, increasing the mean radiant temperature in most cases. Air

temperature is not affected by the canyon’s façades reflectivity while it shows a significant daytime reduction for

increased roads’ reflectivity. The results provide preliminary guidelines for the control of UA and the

improvement of microclimate in London