The impact of building density and building height heterogeneity on average urban albedo and street surface temperature

• The impact of canyon geometry on average urban albedo and street surface temperature are investigated.
• The medium-density urban absorbs the solar radiation most.
• The average urban albedo increase as building height become uniformity.
• Obviously relationship is found between the sky view factor of the canyon and the street surface temperature.

A three-dimensional numerical model (the Model for Urban Surface Temperature – MUST) was used to investigate the impact of urban geometry on average urban albedo and street surface temperature. Satisfactory performance of the model in predicting urban albedo was confirmed. The calculated results for different canyon geometries show that: 1) the medium density urban condition (plan area index λpλp = 0.44) absorbs the most solar radiation and thus has the lowest urban average albedo; 2) the average urban albedo decreases with increasing building height; and 3) in general, more solar radiation is absorbed as building height differences become much greater. Therefore, the average urban albedo is the least for a medium density city having high-rise buildings with greater building height differences. The relationship between sky-view factor and street surface temperature was also examined. The model predicted a cooler urban street surface temperature with a smaller daily amplitude and earlier occurrence of the daily maximum temperature for a high-rise high density city when compared to a low-rise low density city. Horizontal surfaces in an urban area play an important role in determining the average urban albedo. A linear relationship was found between the average sky-view factor of horizontal surfaces and the average urban albedo.