Rising Temperatures: Understanding Urban Heat Island effects in our cities
Why are cities overheating? And what options do we have to prevent it?
By: Faiza Hasan, Research Fellow
About 55% of the global population lives in cities, and with ongoing trends in urbanization, this figure is expected to increase significantly, potentially increasing to 68% by 2050. As cities expand and more people live in urban areas, there are various concerns, a primary concern being heat. The Urban Heat Island effect is a phenomenon where urban areas tend to be higher in temperature than their surrounding rural areas.
A few factors can contribute to these ‘heat islands’ being created, such as overcrowding. Similar to how being in a crowded room can get uncomfortable temperature wise; the hustle and bustle of a crowded city contributes to its heat. While rural areas consist of fewer people spread across more land; urban areas are small, high contact, and full of activity. Having hundreds of vehicles, air conditioning units, industrial facilities, and more, crammed into a small space contributes to higher temperatures.
Additionally, urban areas suffer from a shortage of natural heat reduction capabilities. The absence of trees, vegetation, and bodies of water removes necessary shade and cooling mechanisms that commonly exist in rural areas to cool down the landscape. Instead, materials used to construct facilities in city construction tend to absorb more heat in comparison to trees, vegetation, and bodies of water, contributing further to higher temperatures.
An additional, and very important, perpetrator of the heat island effect is the geometry of a city itself. The ‘urban canyon’ structure refers to the valley formed between tall, closely spaced skyscraper-like buildings in the city. This structure leads to a larger heat capacity and changes in wind pattern through the city, further intensifying the temperature in cities.
What is the Solution to Overheating Cities?
Cities are getting hotter, more people are moving to cities, construction is increasing, heat is being trapped and absorbed…and the cycle continues. Is the solution to stay rural? Should cities be avoided?
As always, there are different arguments, one of them being that natural landscapes are preferable and humans should avoid altering the landscape. Others state that humans are a part of the natural landscape and therefore anything we create is natural. While this debate continues — especially as global heating heightens, there are still ways to make cities more sustainable and reduce the Urban Heat Island effect.
- Changing Construction Materials
Darker colored construction materials absorb more heat, constructing lighter colored roofs and pavement can lower the Urban Heat Index (UHI). Additionally, concrete is known for a high thermal capacity, exploring alternatives such as wood or bamboo can help in reducing temperatures as well. Other newer construction materials such as solar glass, which absorbs heat and converts it to energy, are great options for construction material but are also more expensive than switching to lighter colored materials or avoiding concrete. However, calculating the cost-benefit of these materials in the long term is important as they might reduce energy and cooling costs, such as in the case of Solar glass.
2. Incorporating Green Spaces
The abundance of concrete present in cities increases heat absorption. To combat this, planting trees is a suitable option because it encourages evapotranspiration. As the name suggests, evapotranspiration is a combination of two processes. Evaporation refers to water from surfaces that turns into water vapor. Transpiration is the vapor released by plants as they absorb water through their roots. This process uses heat in surrounding areas, subsequently cooling those areas.
Additionally, trees provide shade, which helps in reducing temperature and shielding people from the sun. However, planting enough trees to make a difference in a crowded city can be difficult. While parks do exist within urban areas, a famous example being Central Park, the rest of the city remains defenseless. Another solution to this issue is constructing more green roofs. They provide shade while also encouraging evapotranspiration, and act as insulation for buildings, thus reducing the overall energy cost needed to heat and cool the building.
3. Careful Urban Planning
Cities need to be planned meticulously, with foresight. The structures built in cities are meant to last and will subsequently impact their surroundings for decades. This longevity means that the choices made during planning and construction will have lasting environmental impacts. So it’s crucial for city councils, urban planners and construction companies to work together for climate-conscious solutions. Key considerations include building geometry, which influences airflow and heat distribution, the selection of materials that minimize heat absorption, and climate friendly green spaces, which will all play a significant role in mitigating overheating in urban areas.
The Muslim Perspective
Islamic law contains the idea of an inviolable sanctuary labeled as the Haram. Both Makkah and Al-Madinah contain these inviolable sanctuaries in which Prophet Muhammad (PBUH) himself stated rules. In Makkah he stated
“Its thorn trees shall not be cut down, its game shall not be disturbed…and its fresh herbage shall not be cut” (Othman Abd-ar-Rahman Llewellyn, “The Basis for a Discipline of Islamic Environmental Law”)
and in Medina he (PBUH) stated similar instructions.
To this day, hunting does not take place within these two areas, but the rest of the environmental rulings aren’t practiced. Since these rulings are ‘incompatible’ with development, it’s been argued that necessity makes what’s prohibited permissible, in this case prioritizing development over environmental consequences (Othman Abd-ar-Rahman Llewellyn, “The Basis for a Discipline of Islamic Environmental Law”). The two inviolable sanctuaries have the potential to become models of environmental protection and sustainable development, showcasing best practice in integrated urban and rural planning. Demonstrating how to live in peace with people and the planet has great potential to spread environmental consciousness throughout the Muslim world and beyond.
There are other tools in Islamic law that can impact how urban design is approached, including harim zones such as greenbelts and easements, as well as himas, the wildlands protected from settlement, farming, wood cutting, etc. in order to protect the areas for public good. We may even consider economic aspects of Islamic law, such as waqf, which can be used as an important material and financial support for conservation.
Earlier the question was posed, is it better to stay rural and avoid urbanization? And reflecting deeper we need to ask, are humans disrupting the landscape? The Islamic response, as always, seems to be moderation, seeking to first remove harm and then bring benefit in consideration to all of creation.
Disclaimer:
Views and opinions expressed in this article are those of the contributors and do not necessarily reflect the views, policy or position of the organization.
Sources:
1- 68% of the world population projected to live in urban areas by 2050, says UN.
2- Heat Islands and Equity.
https://www.epa.gov/heatislands/heat-islands-and-equity#inequitable
3- Reduce Heat Islands.
https://www.epa.gov/green-infrastructure/reduce-urban-heat-island-effect
4- Learn About Heat Islands.
https://www.epa.gov/heatislands/learn-about-heat-islands
5- Using Green Roofs to Reduce Heat Islands.
6- ‘Canyon Effect’ in Australian cities.
https://medium.com/the-machinery-of-government/canyon-effect-in-australian-cities-ce496190c760
7- Evapotranspiration: Watching Over Water Use.
8- Heat Storage in Urban Areas: Local-Scale Observations and Evaluation of a Simple Model.
Grimmond, C. S. B., & Oke, T. R. (1999). Heat Storage in Urban Areas: Local-Scale Observations and Evaluation of a Simple Model. Journal of Applied Meteorology, 38(7), 922–940. https://doi.org/10.1175/1520-0450(1999)038<0922:HSIUAL>2.0.CO;2
9- Thermal Effects of Urban Canyon Structure on the Nocturnal Heat Island: Numerical Experiment Using a Mesoscale Model Coupled with an Urban Canopy Model.
Kusaka, H., & Kimura, F. (2004). Thermal Effects of Urban Canyon Structure on the Nocturnal Heat Island: Numerical Experiment Using a Mesoscale Model Coupled with an Urban Canopy Model. Journal of Applied Meteorology, 43(12), 1899–1910. https://doi.org/10.1175/JAM2169.1
10- Urban storage heat flux variability explored using satellite, meteorological and geodata.
Lindberg, F., Olofson, K.F.G., Sun, T. et al. Urban storage heat flux variability explored using satellite, meteorological and geodata. Theor Appl Climatol 141, 271–284 (2020). https://doi.org/10.1007/s00704-020-03189-1
11-Urban Heat Island: Causes, Effects and Mitigation Measures — A Review.
Md. Nuruzzaman. Urban Heat Island: Causes, Effects and Mitigation Measures — A Review. International Journal of Environmental Monitoring and Analysis. Vol. 3, №2, 2015, pp. 67–73. doi: 10.11648/j.ijema.20150302.15
12- The role of city size and urban form in the surface urban heat island.
Zhou, B., Rybski, D. & Kropp, J.P. The role of city size and urban form in the surface urban heat island. Sci Rep 7, 4791 (2017). https://doi.org/10.1038/s41598-017-04242-2
13- The Basis for a Discipline of Islamic Environmental Law.
LLEWELLYN, O. A.-a.-R. und Harvard University Center for the study of World Religions, 2003. The Basis for a Discipline of Islamic Environmental Law. In: Islam and ecology: a bestowed trust. S. 185–248. Harvard University Press. ISBN 0945454392
