Analysis of the microclimatic impact of greening in high rise urban built environment using site measurements and sky view image processing techniques

Abstract

Urban greening is believed to be capable of providing passive cooling by its shading and evaportranspiration1. High density in high rise milieu could influence greening cooling effects by altering solar and infra-red radiation exchange within so called urban canyons in ways differently with that within low rise settings. One of the most significant differences is that tall buildings can shade the greening at ground level instead of being shaded by them. In this scenario, an increase of built density could dilute cooling effect of greening by both shading and evapotranspiration in daytime, while increase of either building or tree canopy density could hamper irradiative cooling by reducing visible sky area at night. To test this hypothesis, site measurements at typical points in selected high rise residential developments in Shanghai is carried out. Microclimatic data and site-specific parameters are recorded in clear and calm days. A tool to measure built density and tree canopy density is developed using fish eye lens digital sky view imaging and WINSCanopy software. Temporal and spatial variations of microclimatic data are correlated to site parameters to evaluate their significant levels. The findings are useful for landscape and urban planning practice in high rise built environments with an aim to improve their bioclimatic performance and to mitigate urban summer heat islands.