Abstract
The microclimatic conditions of the urban environment influence significantly the thermal comfort of human beings. One of the main human biometeorology parameters of thermal comfort is the Mean Radiant Temperature (Tmrt), which quantifies effective radiative flux reaching a human body. Simulation tools have proven useful to analyze the radiative behavior of an urban space and its impact on the inhabitants. We present a new method to produce detailed modeling of Tmrt spatial distribution using the 3-D Discrete Anisotropic Radiation Transfer model (DART). Our approach is capable to simulate Tmrt at different scales and under a range of parameters including the urban pattern, surface material of ground, walls, roofs, and properties of the vegetation (coverage, shape, spectral signature, Leaf Area Index and Leaf Area Density). The main advantages of our method are found in (1) the fine treatment of radiation in both short-wave and long-wave domains, (2) detailed specification of optical properties of urban surface materials and of vegetation, (3) precise representation of the vegetation component, and (4) capability to assimilate 3-D inputs derived from multisource remote sensing data. We illustrate and provide a first evaluation of the method in Singapore, a tropical city experiencing strong Urban Heat Island effect (UHI) and seeking to enhance the outdoor thermal comfort. The comparison between DART modelled and field estimated Tmrt shows good agreement in our study site under clear-sky condition over a time period from 10:00 to 19:00 (R2 = 0.9697, RMSE = 3.3249). The use of a 3-D radiative transfer model shows promising capability to study urban microclimate and outdoor thermal comfort with increasing landscape details, and to build linkage to remote sensing data. Our methodology has the potential to contribute towards optimizing climate-sensitive urban design when combined with the appropriate tools.
Highlights
The scene elements were grouped by surface material, allowing them to be linked to their respective surface temperatures and optical spectral properties in the Discrete Anisotropic Radiation Transfer model (DART) database
Our motivation to use the DART model to estimate Tmrt stems from its capability to assimilate a large variety of 3-D data derived from state-of-the-art remote sensing techniques; providing the possibility to better analyze how Tmrt is influenced by vegetation and its biophysical properties, by the optical properties of surface materials, by surface temperature, and by local atmospheric conditions
The increasing availability of data of urban areas opens up new possibilities for detailed analysis in terms of urban microclimate and thermal comfort
Summary
The increased number of heat waves due to global climate change experienced in growing urban areas across the world directly and indirectly affects thermal comfort and health of urban residents, in the tropics. The environmental factors controlling outdoor thermal comfort are the Mean Radiant Temperature (Tmrt), wind speed, air temperature, and humidity [1]. Outdoor thermal comfort and heat related mortality are more influenced by the Tmrt and less by the other three factors [2]. Tmrt is considered an essential bio-meteorological variable having a strong influence on thermal comfort indices
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