Some of Bangkok’s low-income communities suffer the impacts of extreme heat due to inadequate housing or lack of cooling measures, and internal room temperatures are often 10 degrees hotter than their surroundings. This poses health risks and economic costs. Analyzing the land surface temperature (LST) and identifying urban localities suffering high heat effects can help with urban planning and social support to counter the risks of heat for many vulnerable communities.
Urban dwellers worldwide are feeling the heat intensifying by the year . During the hot season in Bangkok, the increasing global temperature, compounded by the urban heat island (UHI) effects , turns a sunny, cloudless day in the city into an intense, searing experience.
This extreme heat is a discomfort that middle- to high-income households can often afford to escape, but it’s a month-long unavoidable reality for low-income households to endure. With this in mind, SEI researchers decided to visit Khlong Toey at noon in April—the hottest time and month in Thailand—to ask how the residents in the largest informal settlement of Bangkok—with over 100,000 inhabitants—were coping with the heat and what we could learn from them.
Khong Toey’s houses are mostly built with low-cost materials such as metal sheet roofs, gypsum plasters, and concrete blocks, that serve to absorb more solar radiation 1 and have a high heat capacity and thermal conductivity (Figure 1). This makes the ambient air temperature hotter than the meteorological readings. Most of the housings lack, or at best improvise, insulation under their roof with plastic sheets and material they can get hold of, to minimize the heat transfer from the roof to their room.
The setup of the housings also undermines the ability of residents to improve indoor and outdoor thermal comfort. As housing formations are densely lined side-by-side along the shadeless streets, they feel the heat radiating from the concrete street (64.0 C) and through their roof (62.2 C). The houses often lack channels for ventilation (e.g. windows) and can accumulate heat transferring from the roof. This makes the houses hot and humid. Most households are low-income and cannot afford to invest in air conditioning systems.
We visited two housing quarters at 1 pm, the time the locals said is the hottest in the day. Equipped with an infrared and digital thermometer, we captured the surface and air temperature in those spots. At the time, when the temperature on our iPhone weather app read 37 C, we found the temperature in those spots was significantly higher.
The first house (Figure 3) that was directly feeling the brilliant shine of the sun had an air temperature inside the house of 39.3 C with 70 percent relative humidity. The surface temperature of the floor, wall, ceiling, and metal roof read 41.1 C, 45.7 C, 49.2 C, and 68.1 C, respectively. The fact that the housing has just one air outflow from the entrance door technically makes natural ventilation non-existent. This makes the feeling inside – even just a few minutes – hot, sticky, and draining. The air was wet and heavy (Figure 4).
In contrast to the second housing quarters that fortunately sit under a tree’s shade (Figure 5), the housing had an air temperature of 35.5 C with 65 percent relative humidity. The surface temperature of the floor, wall, ceiling, and metal sheet roof was noticeably lower than the first house at 39.8 C, 40.2 C, 41.6 C, and 45.5 C, respectively. Hot, but significantly cooler than the first house that did not have any shading.
When asked how the people were coping with the heat, they told us various ways they were adapting to the heat. Both tenants said they simply cannot stay inside their home during the daytime (1 pm – 4 pm) as being in their house feels like being in a roasting oven. Some households run a water sprinkler over their metal sheet roof to reduce the heat transfer to their living space. In this oppressive heat, the community leader said every moment of wind breeze brought instant relief. Many carried cloth soaked in cold water to dab their body through the day and night. Ice is a precious and sought-after commodity. Some people just throw themselves against the open fridge for a few seconds of cooling. At nighttime, people got used to sleeping in bedsheets that quickly became soggy from their own sweat. It is common for the people of Khlong Toey to wake up two to three times from 10 pm to 4 am, to have a ‘cool off’ shower.
Studies show that increasing nighttime temperature, compared to daytime, has a disproportionately higher health impact because insufficient sleep is linked to adverse physical and mental impacts. The accumulated stresses from heat and sleep deprivation become dangerous for elderly women and children 2. As the people of Khlong Toey are reportedly experiencing poorer quality sleep, higher sleep disruption, and lower sleep time due to the heat, it raises critical questions about how municipalities can mitigate the UHI effect and improve thermal comfort as Bangkok’s temperature increases.
With the surface and air temperature readings, we can extrapolate the data with remote sensing for long-term temperature projections. Today’s high-resolution aerial and satellite data has enabled us to accurately and precisely monitor temperature changes in the physical environment. By leveraging a suite of accessible satellite data, like MODIS, Landsat, and Sentinel, we can efficiently analyze the land surface temperature (LST) and UHI effect.
By incorporating LST analysis into the decision-making process, we can identify the urban localities with high UHI effects and people vulnerable to these effects. The information creates the ground for urban planning and social support to counter the heat risk. Specifically, an urban cooling strategy, e.g., Cooling Singapore, formulated a city-scale plan to reduce the UHI effect and improve outdoor thermal comfort. Pairing the research insight with a community-led plan can co-produce a targeted urban cooling strategy that reduces the urban heat risk of vulnerable social populations and improves livability, e.g., promoting green spaces in reducing overall heat island temperatures.
It is a matter of ‘when’ – not ‘if’ – to develop a city and district strategy to manage the UHI effect and improve outdoor thermal comfort in Bangkok. Without it, municipalities and communities will be inescapable in a hotbox enclave.
Qi, J.-D., He, B.-J., Wang, M., Zhu, J., & Fu, W.-C. (2019). Do grey infrastructures always elevate urban temperature? No, utilizing grey infrastructures to mitigate urban heat island effects. Sustainable Cities and Society, 46, 101392. https://doi.org/10.1016/j.scs.2018.12.020; and Radhi, H., Assem, E., & Sharples, S. (2014). On the colours and properties of building surface materials to mitigate urban heat islands in highly productive solar regions. Building and Environment, 72, 162–172. https://doi.org/10.1016/j.buildenv.2013.11.005
Chevance, G., Minor, K., Vielma, C., Campi, E., O’Callaghan-Gordo, C., Basagaña, X., Ballester, J., & Bernard, P. (2024). A systematic review of ambient heat and sleep in a warming climate. Sleep Medicine Reviews, 75, 101915. https://doi.org/10.1016/j.smrv.2024.101915; and Sánchez-Guevara Sánchez, C., Núñez Peiró, M., & Neila González, F. J. (2017). Urban Heat Island and Vulnerable Population. The Case of Madrid. In P. Mercader-Moyano (Ed.), Sustainable Development and Renovation in Architecture, Urbanism and Engineering (pp. 3–13). Springer International Publishing. https://doi.org/10.1007/978-3-319-51442-0_1
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