Heat-Mitigation Strategies to Improve Pedestrian Thermal Comfort in Urban Environments: A Review

Abstract

Thermal comfort is one of the main factors affecting pedestrian health, and improving thermal comfort enhances walkability. In this paper, the impact of various strategies on thermal-comfort improvement for pedestrians is thoroughly evaluated and compared. Review studies cover both fieldwork and simulation results. These strategies consist of shading (trees, buildings), the orientation and geometry of urban forms, vegetation, solar-reflective materials, and water bodies, which were investigated as the most effective ways to improve outdoor thermal comfort. Results showed that the most important climatic factors affecting outdoor thermal comfort are mean radiant temperature, wind speed, and wind direction in a microclimate. The best heat-mitigation strategy for improving thermal comfort was found to be vegetation and specifically trees because of their shading effect. The effect of height-to-width (H/W) ratio in canyons is another important factor. By increasing H/W ratio, the thermal-comfort level also increases. Deploying highly reflective materials in urban canyons is not recommended, as several studies showed that they could reflect solar radiation onto pedestrians. Results also showed that, in order to achieve a satisfactory level of thermal comfort, physiological and psychological factors should be considered together.

The Use of Green Design Strategies for Achieving Thermal Comfort (Applying PMV as a Measurement Tool)

“…In many research studies, ENVI-met has proven its success in performing thermal simulations for outdoor areas. (M. Fahmy, Mahmoud, Elwy, & Mahmoud, 2020;Gehl Jan, 1996;Yang et al, 2011;Yilmaz, Mutlu, & Yilmaz, 2018;Nasrollahi, Ghosouri, Khodakarami, & Taleghani, 2020).These studies confirmed an agreement between the measured data (from the field measurements or observed data at the local meteorological stations) and simulated air temperatures. Envi-met has the capability to simulate the microclimate of any location all over the world.…”

“…Therfore, water bodies are inputted as a type of soil, and the process is limited to the transmission and absorption of the shortwave radiations. (Nasrollahi et al, 2020)…”

The Challenge in the Management of Historic Trees in Urban Environments during Climate Change: The Case of Corso Trieste (Rome, Italy)

“…Urban vegetation can make a significant contribution to climate change adaptation and mitigation strategies by cooling cities through shading and evapotranspiration, by mitigating the effects of wind speed and turbulence helping enhance pedestrian comfort, by slowing and filtering the runoff from rain events, contributing to improve water quality, and to reduce storm water runoff, flooding, and waterway pollutants and by filtering atmospheric pollutants include nitrogen dioxide and sulphur dioxide, and larger particulate matter [6][7][8][9][10][11]. However, the potential of these effects depends on the phytosanitary and biological status of the vegetation.…”

“…It is important to consider that vegetation in the urban environment is stressed by anthropic and natural factors exacerbated by climate change. Specifically, climate change influences plants at all stages of development: germination, growth, and reproduction [9]. Temperature and water availability affect the timing and success of seed germination and disrupt pollen development and fertilization [12] and reduce its viability [13], and directly affect photosynthesis and growth rates; in particular, drought reduces growth by inducing stomatal closure and decreasing photosynthetic capacity [14].…”

Implications of Urban Land Management on the Cooling Properties of Urban Trees: Citizen Science and Laboratory Analysis

“…Various other studies have attempted to quantify the respective contribution of each of the processes involved in the cooling effect, which combines a radiative component and an evaporative component, i.e., shading and transpiration [7,45]. Various studies used either field measurements (e.g., [46][47][48][49]) or model simulations (e.g., [50][51][52]). Nevertheless, more effort is needed to improve our understanding of the effects that landscaping and land management has on leaf area and transpiratory cooling of trees.…”