Urban design to lower summertime outdoor temperatures: An empirical study on high-rise housing in Shanghai

This research investigates the effect of urban design factors on summertime urban heat island (UHI) intensity. Ten high-rise residential quarters in the inner city of Shanghai were empirically investigated during mid July to mid August in 2008. On-site design variables were developed to quantify the thermal impacts from density, building layout and greenery. The design variables that were measured on site were correlated with the variation in UHI intensity during the day and night. The results show that variations in UHI are in part due to site planning, building design, and greenery. The overall daytime and nighttime UHI models explain up to 77 and 90 percent of UHI variation, respectively. On-site shading from either buildings or vegetation canopy is the most important factor influencing daytime UHI. The shading factor can distort and dilute behavior of other variables, e.g., green ratio and surface albedo. Nighttime UHI is more complicated due to the influence from anthropogenic heat, and is significantly related to greenery density and coverage. Based on the findings, potential design strategies are proposed in an effort to mitigate UHI, including manipulating building layout and mass to improve shading during the day while facilitating site ventilation at night and increasing site vegetation cover through strategic tree planting. Further recommendations for urban planning approaches to mitigate UHI on the urban scale are proposed.