Urban Heat Island: Why are our cities getting hotter?

Date Published: August 13th, 2024

Written by: Vania Dian Gunawan, edited by Charlene Octavian

Graph showing surface temperature differences between day and night in urban vs. rural areas

Source: U.S. Environmental Protection Agency

If you’re living in urban areas, especially in the tropics, you’ve likely experienced the discomfort of going out under the scorching hot sun during summer or the dry season, wishing you could escape to the cooler, breezy countryside. This phenomenon is known as the Urban Heat Island (UHI), it happens mostly in metropolitan areas, where usually the temperature is higher than the surroundings. Urban areas are places where many people are densely constructed in certain spaces.

The world is experiencing a significant shift towards urbanization. Currently, over 50% of the global population resides in cities, a rise from about one-third in 1950, and it is anticipated that this number will grow to approximately two-thirds by 2050. This rapid urbanization will make the UHI an increasing problem for many people around the world.

In Indonesia, the UHI effect is also evident. Suburban areas around Jakarta, including Depok, Bogor, South Tangerang, and Bekasi, are experiencing significant residential expansion. This growth has led to increasing temperatures, with average land surface temperatures (LST) recorded at 27.97°C in 2004, 30.82°C in 2014, and 28.7°C in 2020. LST was lower in 2020 compared to 2014 because of the climatic effects of La Niña in the latter part of the year which leads to cooler surface temperatures worldwide, in contrast with El Niño. Besides residential expansion, the increase in LST is also linked to the growth of barren land and a decrease in vegetation and water bodies.

The same research also shows that in Jabodetabek and the surrounding cities of Tangerang, South Tangerang, and Bekasi, the UHI effect causes ground surface temperatures to be 3-6 °C higher than in nearby rural areas.

This increasing temperature will not only negatively affect the environment but also threaten human health. Before we go further into the effects of UHI, let’s first understand the causes and then explore what can be done to mitigate it.

Causes of Urban Heat Island

Urbanization & human activities

The growing number of people coming to the urban area every year exacerbated this effect because of their activities that generate heat such as industrial, transportation, energy consumption, and construction.

Lack of green areas

Urbanization has led to land use changes to accommodate people’s needs. Modifications such as deforestation, clearing of vegetation, and changes in land cover, and landscape could affect the heat and moisture exchange between the land surface and the atmosphere, worsening the UHI effect.

Buildings are constructed close together

Building materials are usually good at retaining heat, so when homes, shops, and industrial buildings are built close to each other, it can lead to increased temperature in the surrounding areas.

Albedo effect

This refers to the reflectivity of surfaces. Dark materials like asphalt, concrete, roofs have low albedo meaning they absorb more heat. As a result, temperatures remain high at night as the absorbed heat rises into the atmosphere, keeping the surroundings warm.

Tall urban buildings

Tall buildings create ‘urban canyons’ that block cooling winds and trap heat.

Effects of Urban Heat Island

Human health, productivity, and comfort

Increase the risk of heat stress leading to heat exhaustion, heatstroke, and dehydration, especially among vulnerable groups like children, the elderly, and those with existing health issues.

Worsen air quality by promoting the formation of ground-level ozone and fine particulate pollution. Ground-level ozone, formed through complex chemical reactions involving pollutants and sunlight, increases respiratory and cardiovascular risks among urban residents.

Create favorable conditions for the spread of vector-borne diseases, such as dengue fever and malaria.

These health risks, combined with reduced productivity from heat-related discomfort and illnesses, lower the overall quality of life and limit people’s ability to work and engage in daily activities.

Environment and Climate

Energy Consumption: UHI contributes to increased energy consumption for cooling, leading to higher greenhouse gas emissions and energy costs. There’s an unending loop where when the very hot days can also further worsen the heat because people try to cool themselves with air conditioners.

Hydrological Cycle: UHI effects can disrupt local hydrological cycles by reducing evapotranspiration, potentially leading to droughts in some areas.

Biodiversity: Higher temperatures, less vegetation, and changes in water availability can harm plant and animal species, leading to habitat loss. Additionally, warm water flowing into local streams can disrupt ecosystems and exacerbate environmental changes, making it difficult for species adapted to cooler habitats to survive.

How to Mitigate Urban Heat Island

Greeneries can reduce the urban heat island effect in urban areas.

Photo by CHUTTERSNAP on Unsplash

Proper urban design & planning

Considering the characteristics of the local climate and meteorology and green building concepts such as:

Add greenery to cities to help cool things down. Plant trees along streets to provide shade, especially over dark surfaces, and add vegetation into urban spaces, including green roofs. Plants and trees can absorb pollutants, cooling the temperatures, conserve water, and shield people from UV light.

Implement high albedo materials for surfaces on roofs, roads, and walls. Other than implementing green roofs or walls, this can also be done by renovating the existing ones or making the new ones with light reflective colour and coating to reduce heat trap.

Vary the height of new buildings to increase airflow, create shade canyons, or use more natural ventilation in buildings

Limit land use change by maintaining green open spaces and designated green zones. Strong policies are needed to ensure that land intended to remain undeveloped is protected from land-use changes.

Use permeable paving to let water flow through and facilitate evaporation, which has a cooling effect.
Building on stilt can reduce the UHI effect and save energy by naturally cooling the building as cool air circulates underneath. This method is also more common in tropical countries and can be considered eco-friendly as it causes minimal harm to the landscape.

Individuals can help by choosing public transportation, using more energy-efficient appliances, planting more plants and vegetation, and implementing sustainable house design. The effect of implementing this in just one building might not create a significant change, but if people start implementing it in multiple buildings, collectively it can reduce the UHI in some areas.

How Eco-Mantra’s Projects Showcase Minimized Environmental Impact While Improving Thermal Comfort

Batavia & Central Market PIK

Eco-Mantra is involved in the Environmentally Sustainable Design (ESD) Concept and Schematic Design for Batavia PIK and Central Market in North Jakarta. They have implemented various ESD features to improve thermal comfort in these properties.

In Batavia PIK, ESD features recommended could not only potentially reduce ambient temperature but also ultimately increase asset utilization and reduce turnover rates by a factor of 6 hours per day, resulting in more visitors during the day due to the cooler, more comfortable temperature. Some of the ESD features recommended and implemented are building on stilts and mangrove restoration, where mangrove CO₂ sequestration is 80 times more effective than that of a tropical rainforest.

For Central Market PIK, other than ESD Concept and Schematic design, Eco-Mantra also assisted Central Market PIK in achieving EDGE Advanced Green Building Certification, making it the first eco-lifestyle hub in Indonesia to receive it. Some of the strategies include installing a heat-reflecting skylight and stack effect ventilation to enhance natural ventilation and air circulation.

Eco-Mantra is an environmental engineering consultancy company that helps implement ESD in client properties. We offer a wide range of services for companies and leaders at any stage of the sustainability journey, from consulting and auditing to design and engineering.

If you are interested in implementing ESD in your project, please contact us here. We will be happy to assist you with our expertise and experience. Together, we can create a greener future for ourselves and our planet!