Urban Heat Island mitigation strategy
Green wall installation can provide cooling effects for both indoor and outdoor environments.
Image Credit: Osaka Metropolitan University
Scientific Frontline: Extended "At a Glance" Summary: Urban Heat Island Mitigation Strategies (UHIMS)
The Core Concept: Urban Heat Island Mitigation Strategies (UHIMS) encompass ecological and architectural interventions—such as vertical greenery and reflective surfaces—designed to reduce extreme localized temperatures in urban environments by managing how building envelopes interact with local microclimates.
Key Distinction/Mechanism: Unlike traditional approaches that isolate indoor air conditioning or outdoor shading, advanced UHIMS operate dynamically across the building envelope. By utilizing vertical greenery and targeted surface albedo (reflectivity), these strategies simultaneously cool indoor spaces and outdoor immediate environments without relying on active electrical grids.
Major Frameworks/Components:
- Building Energy Model (BEM): A simulation framework used to reproduce, analyze, and predict indoor thermal conditions and overall energy performance.
- Urban Microclimate Model (UMM): A spatial analytical tool utilized to capture outdoor microclimate dynamics and environmental interactions.
- Physiologically Equivalent Temperature (PET): A standardized bioclimatic metric used to consistently assess human thermal comfort across both indoor and outdoor settings.
- Surface Albedo Modulation: The strategic use of surface reflectivity, where high-albedo materials reduce indoor temperatures, and low-albedo exterior surfaces enhance localized outdoor thermal comfort.
Branch of Science: Urban Climatology, Building Physics, Human Ecology, and Sustainable Architecture.
Future Application: The development of passive-cooling, resilient building envelopes designed to maintain survivable human thermal conditions during compounded climate emergencies, such as extreme heatwaves occurring simultaneously with regional power outages.
Why It Matters: As global urbanization and climate change accelerate the frequency of extreme heat events, integrated architectural strategies reduce dependency on active cooling systems, lower the strain on vulnerable power grids, and safeguard public health.
Have you ever stood in the middle of a city and felt the heat radiating off its surfaces, or entered a closed room and wondered how it could feel hotter than it does outside?
Climate change and urbanization have intensified the urban heat island (UHI) effect, where urban areas are significantly warmer than rural areas. This has, in turn, increased the frequency of extreme heat events, such as heat waves, and deteriorated both outdoor environments and indoor thermal conditions in buildings, leading to higher cooling energy demands, greater strain on power grids, and an elevated risk of power outages. Previous studies on UHI mitigation have primarily focused on improving outdoor environments, but indoor and outdoor thermal conditions interact dynamically through building envelopes, the materials separating the interior and exterior. Therefore, it is essential to evaluate them in an integrated manner. Furthermore, building resilience under compounded extreme conditions, such as heat waves coinciding with power outages, has not been sufficiently investigated.
To address this, an international research team led by Associate Professor Jihui Yuan from Osaka Metropolitan University’s Graduate School of Human Life and Ecology evaluated the impacts of UHI mitigation strategies (UHIMS)—such as green roofs, vertical greenery, and envelope materials—on both indoor and outdoor thermal environments. The study focused on an educational facility in Shahrud, Iran, a city characterized by extremely hot summers. In the analysis, the researchers used an integrated simulation approach that combines a building energy model (BEM), which reproduces indoor thermal conditions, with an urban microclimate model (UMM), which captures outdoor microclimate dynamics. Based on weather data records, the simulations considered future climate scenarios as well as extreme conditions, including summer heat waves and power outages, to evaluate building performance under realistic and severe conditions. Thermal comfort was assessed using the physiologically equivalent temperature (PET), enabling consistent evaluation of both indoor and outdoor environments.
The results revealed that a green wall installed on the south-facing facade improved indoor thermal conditions by up to 1.7°C. In addition, albedo, the amount of light reflected by a surface, showed significant effects on thermal comfort. Low-albedo exterior surfaces improved outdoor thermal comfort by approximately 1.5°C, while high-albedo exterior surfaces were found to be particularly effective in reducing indoor temperatures. Additionally, researchers found that the radiative properties of exterior materials have a stronger influence on thermal environments than their heat capacity.
“This study could function as an initial guide for resilient buildings that can maintain acceptable thermal conditions even under extreme conditions,” said Yuan. “It could also contribute to the advancement of urban heat island mitigation strategies that integrate both urban- and building-scale approaches, while helping to achieve both reduced energy consumption and improved thermal comfort.”
Published in journal: Energy and Buildings
Authors: Parnian Komeili, Mostafa Mohajerani, Ahmad Jameei, Masoud Taheri Shahraeini, and Jihui Yuan
Source/Credit: Osaka Metropolitan University
Edited by: Scientific Frontline
Reference Number: eco061526_01
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