Horizontal Heat Impact of Urban Structures on the Surface Soil Layer and Its Diurnal Patterns under Different Micrometeorological Conditions

The temperature of the surface soil layer around different orientation walls was investigated horizontally along several construction-soil micro-gradients in Beijing, China. On a diurnal scale, similar fluctuating trends in T 0 and T 50 (temperature of surface soil layer, 0 and 0.5 m from the building baseline) adjacent to the external walls of buildings with the same orientation usually appeared under similar micrometeorological conditions. The difference between T 0 and T 50 (ΔT 0–50 ) can be considered an indicator of the intensity of the horizontal heat effects: higher ΔT 0–50 values correspond to greater intensities. The values of ΔT 0–50 for south-, north-, east- and west-facing sides of buildings were highest on sunny days in summer and exhibited values of 6.61 K, 1.64 K, 5.93 K and 2.76 K, respectively. The scope of horizontal heat impacts (S h ) changed on a diurnal scale between zero and the maximum, which fluctuated with the micrometeorological conditions. The maximum values of S h were 0.30, 0.15, 0.20 and 0.20 m for south-, north-, east- and west-facing walls. The ΔT 0–50 was related to solar radiation, horizontal heat flux, relative humidity, wind speed, soil moisture differences and air temperature; the relative importance of these factors was 36.22%, 31.80%, 19.19%, 2.67%, 3.68% and 6.44%, respectively.