A big picture of urban heat island mitigation strategies and recommendation for India
Introduction
In the recent past, the earth's ecology has witnessed climate change. Scientists have researched that global temperature will continue to rise for decades due to greenhouse gases produced by human activities which include the use of air conditioning for thermal comfort. Global climate change due to various other reasons and one of the reasons is rapid urbanization in large cities is worsening the liveability status of the people living in the cities and their surroundings. Currently, more than 50% of the world population lives in urban areas, and it is expected to increase to 6.4 billion by 2050 (Bocquier, 2005).
It has been established that an increase in global temperature has a direct impact on the microclimate. There are many factors that trigger climate change, and consequences afterward. One of the after-effects is Urban Heat Island (UHI), recognized as the most evident characteristics of urban climate. It occurs due to dark, non-reflective surfaces used for parking, roads, roofs, walkways. As urban areas developed, open land and vegetation have been replaced by buildings, roads, landscapes and other infrastructure. These surfaces absorb the warmth of the Sun and radiate heat. The increase of land surface temperature influence material flow and energy flow in urban ecological systems, employing a series of environmental effects on urban climates and human health.
According to a study of the metropolitan area of Chicago and Salt Lake City by the LBNL, the energy-saving potential of heat island reduction measures ranges from $4 million to $15 million per year (Konopacki and Akbari, 2002).
The present paper assesses various heat island mitigation strategies and their effectiveness in cooling the urban environment. It also proposes a set of recommendations for India based on research and analysis. It includes an extensive overview with a focus on the measures-specific approach to UHI mitigation. The present paper provides policies or programs to identify and spread successful approaches as time and cost-efficiently as possible.
Section snippets
Impact of urban heat island
A community's environment and its quality of life can be affected by the increased temperatures from urban heat islands, especially during the summer. Though some heat island impacts appear positive like the expansion of the plant growing season, most impressions are negative and includes:
Benefits of urban heat island mitigation
Mitigating the urban heat island effect can produce benefits for buildings, cities, suburban areas, and globally as well. There can be a:
- •
Reduction in energy bills in Air-conditioned buildings and unconditioned buildings can be cooler in the summer months
- •
Reduced thermal expansion in roof and thus extended life
- •
Peak shaving of electric demand during the summer months because of reduced building cooling loads
- •
Adverse health and mortality impacts may reduce during extreme heat events.
- •
Improved air and
Strategies to mitigate UHI
There are numerous strategies to mitigate the UHI effect, leaving a positive impact on both local and global climate. The mitigation strategies have been sub-divided into three parts:
- •
Roof strategies (high-reflectance roof, vegetated roof),
- •
Non-roof strategies (shading structure with energy generation/architectural devices, high reflectance paving, plantation, and water bodies) and
- •
Covered parking strategies.
By using these strategies, UHI effects could be significantly reduced. It has been found
Roof strategies
Dark, non-reflective surfaces used for car parking, roads, roofs, walkway, and other hardscapes absorb the sun's warmth and radiate heat, thus creating heat islands. Urban areas can have temperatures 1 to 3 °C (Zielinski, 2014) hotter than nearby suburban and undeveloped areas. Following are the roof strategies that have been discussed to mitigate the effect of UHI.
Vegetation
The presence of vegetation in open spaces within urban areas has a relevant impact on the urban heat island phenomenon with a bulk of effects on the different terms of the surface energy balance. Vegetation in urban open areas can make many contributions to high-quality urban living. It can stop radiation, decelerate wind, and reduce air temperature and plays a key role in the urban thermal environment.
Trees efficiently decrease the thermal radiation in urban open spaces and contribute to the
Covered parking strategies
Parking lots can cover up to half of the land area in cities and offer a great opportunity to correct urban climate problems. The conversion from asphalt-covered parking areas to grass-covered parking areas is helpful to reduce the urban heat island effect. The parking area can be covered with at least one of the following methods: (a) have SRI coated roof; (b) a vegetated roof; (c) covered with energy generation systems such as thermal collectors, photovoltaics and wind turbines.
Recommendations
Urban design plays a major role in heat island formation, and smart growth development strategies provide an opportunity to reduce heat islands. Smart growth increases the community's economy and safeguards the environment through strategies that help citizens to make well-informed decisions regarding the built environment. In addition to limiting the heat island effect, smart growth provides a framework that increases regional environmental protection, enhancement in the community character,
Conclusion
Urban open spaces with a suitable thermal environment attract citizens and boost the vitality of cities. The thermal environment in outdoor spaces can be decomposed into air temperature, thermal radiation, wind speed, and humidity. The present paper reviewed a number of literature and the effectiveness of different mitigation strategies in modifying the urban thermal environment. The following conclusions can be drawn from the literature review:
- •
Urban geometry changes the radiative and
Declaration of Competing Interest
The authors declare that they have no objection and conflict of interest to publish this paper in your journal.
References (46)
- et al.
Global cooling updates: reflective roofs and pavements
Energy Build.
(2012) - et al.
Monitoring the energy-use effects of cool roofs on California commercial buildings
Energy Build.
(2005) - et al.
Urban green space cooling effect in cities
Heliyon
(2019) - et al.
Microclimate development in open urban spaces
Energy Build.
(2015) - et al.
Cool roofs in China: policy review, building simulations, and proof-of-concept experiments
Energy Policy
(2014) - et al.
Development for cool roof calculator for India
Energy Build.
(2016) - et al.
Performance evaluation of green roof and shading for thermal protection of buildings
Build. Environ.
(2005) - et al.
A review of mitigating strategies to improve the thermal environment and thermal comfort in urban outdoor spaces
Sci. Total Environ.
(2019) - et al.
Water as an urban heat sink: blue infrastructure alleviates urban heat island effect in mega-city agglomeration
J. Clean. Prod.
(2020) - et al.
Influence of changing trees locations on thermal comfort on street parking lot and footways
Urban For. Urban Green.
(2017)
Hotspots of solar potential in India
Renew. Sust. Energ. Rev.
Impact of a cool roof application on the energy and comfort performance in an existing non-residential building. A Sicilian case study
Energy Build.
Using Cool pavements as a mitigation strategy to fight urban Heat Island—A review of the actual developments
Renew. Sust. Energ. Rev.
Cooling the cities–a review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments
Sol. Energy
The potential for cool roofs to improve the energy efficiency of single Storey warehouse-type retail buildings in Australia: a simulation case study
Energy Build.
The effects of street tree planting on urban heat island mitigation in Montreal
Sustain. Cities Soc.
Investigation of thermal benefits of rooftop garden in the tropical environment
Build. Environ.
Quantifying the direct benefits of Cool roofs in an urban setting: reduced cooling energy use and lowered greenhouse gas emissions
Build. Environ.
Numerical simulation of the impact of different vegetation species on the outdoor thermal environment
Urban For. Urban Green.
Cool Roof Rating Council
Using Cool Roofs to Reduce Energy Use, Greenhouse Gas Emissions, and Urban Heat Island Effects: Findings from an India Experiment
Thermal comfort for all
Mitigating Urban Heat Island Through Green Roofs
Cited by (30)
Quantifying urban heat island and pollutant nexus: A novel geospatial approach
2024, Sustainable Cities and SocietyAwareness and willingness to pay for green roofs in Mediterranean areas
2023, Journal of Environmental ManagementAssessment of the potential of green wall on modification of local urban microclimate in humid tropical climate using ENVI-met model
2023, Ecological EngineeringCitation Excerpt :The maximum solar insolation measured in Pathanamthitta, Kerala (in this study) was 768 W/m2 in the summer season and 850 W/m2 in the winter season. It may also be noted that green walls are recommended as a suitable potential mitigation strategy for mitigating the urban heat island effect in tropical climates (Khare et al., 2021). Thomas et al. (2018) reported that the intensity of the urban heat island of the study area was 2.6 °C during summer and 2.0 °C during winter.