The influence of urban design on outdoor thermal comfort in the hot, humid city of Colombo, Sri Lanka

Abstract

The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.

Green-Roof Effects on Neighborhood Microclimate and Human Thermal Sensation

“…Therefore, there is constant tendency for numerical models such as ENVI-met to moderate extreme values and contract the diurnal range. Similar results have been reported by Johansson et al [24] and Emmanuel et al [18].…”

“…Human thermal comfort (HTC), which depicts human sensory perception of the thermal environment, has been widely adopted to examine the relative sustainability of urban design options from the human-health viewpoint [18,21,24]. HTC depends on some key weather parameters such as radiation, temperature, humidity and air flow.…”

Urban Outdoor Thermal Comfort of The Hot-Humid Region

“…Interest in research on outdoor thermal comfort has been increasing lately, especially in tropical regions [1], [2], [3], [4], [5], [6]. Not until recently, it has been assumed that the indoor thermal comfort theory can be applied to the outdoor.…”

Sky View Factors from Synthetic Fisheye Photos for Thermal Comfort Routing—A Case Study in Phoenix, Arizona

“…The 1D RayMan model (Matzarakis et al, 2007 has been extensively employed to estimate MRT, PET, and other thermal comfort indices from fisheye photographs, meteorological, and personal factors (Coutts, White, Tapper, Beringer, & Livesley, 2016;Herrmann & Matzarakis, 2012;Johansson & Emmanuel, 2006;Krüger, Minella, & Rasia, 2011;Lin, 2009;Lin, Matzarakis, & Hwang, 2010;Oliveira, Andrade, & Vaz, 2011;Thorsson, Lindqvist, & Lindqvist, 2004), following equations outlined in the German VDI engineering standards (Verein Deutscher Ingenieure, 1994). We automated the Windows GUI using a script that simulates keystrokes to remotely execute the RayMan tool and batch process thousands of georeferenced synthetic fisheyes for a given day and time.…”