An analysis of microclimatic variation in a suburban environment

Abstract

An observational and modeling study of the microclimate of a suburban area, as related to the physical and biological nature of the site, is presented. The measurements and calculations are made in comparison with a nearby open agricultural location or “control site”. The measurement program was conducted during the summer of 1981 in Davis, CA, and consisted of a series of paired observations in which simultaneous measurements were made at a control site, located in a nearby rural area, and one suburban site at a time. Results indicate that this methodology was generally successful. The various suburban sites were as often cooler than the rural site as they were warmer. In one case, a suburban site was found to be substantially cooler, averaging 7.38°C over a 5 day period, than the rural site. This special case was observed to be associated with unusually dry environmental air resulting in large evaporative cooling in the plant canopy. Comparison between the suburban temperature deficit and the physical nature of the various sites reveals that canopy height explained most of the variance of this data set. Two generally important mechanisms are hypothesized to be operating in this system: the effect of canopy size on turbulent mixing and on site shading, especially of paved areas. A simple energy balance model was applied to study the processes that control the daytime suburban temperature deficit. In particular, it is found that suburban sites can be as cool as observed when the following conditions are obtained: low-canopy humidity, large canopy size, low wind speed and high radiation load. The model simulated the overall average suburban temperature deficit of all sites for physically reasonable choices of model parameters. It is pointed out that the fact that suburban areas may be cooler than surrounding rural areas may have significance to the problem of assessing the role of the urban heat island in relation to possible global warming.