"Unsustainable cities accelerate the urban heat island effect"
Bangladesh braced for a ferocious summer with roasting temperatures this year. Not only Bangladesh, various countries have been witnessing hotter and drier summers across the world due to climate change, reckless urbanisation, lack of dark surface and greenery, and so on. Scientists and environmentalists have repeatedly been warning of harsher summers with scorching temperatures.
Dhaka, the capital city of Bangladesh experienced its hottest days in 58 years on 15 April with the mercury climbing up to 40.4 degrees. People have been suffering immensely due to extreme heat throughout April and May across the country. The soil turned bone dry while the temperature kept rising. Although the heat eased a little after Cyclone Mocha had made landfall, further heat waves are predicted in the offing. Heat waves and extreme temperature due to a variety of reasons have been making headlines for the past few days.
This year, a study was conducted about the threat of extreme hot weather for the first time in South Asia. The study report was published in the international scientific journal 'Sustainable Cities and Society' this March. The four researchers who conducted the study, 'Spatiotemporal Changes in Population Exposure to Heat Stress in South Asia', examined the extent to which South Asians are exposed to heat stress and its temporal and spatial effects.
Shamsuddin Shahid is one of the four researchers of the study. He is an associate professor in the Faculty of Civil Engineering at Universiti Teknologi Malaysia (UTM). He has been recognised as one of the World's 1000 most influential climate scientists by Thomson Reuters in 2021. He spoke in an interview with Prothom Alo's Farjana Liaqat about the study, the rising temperature and other details.
Extreme heat does not cause visible damage to the landscape like floods, cyclones or tsunami which is why it remains underestimated. In this context, how can this issue be addressed?
You're correct. Extreme heat is often underestimated due to its lack of visible damage, unlike many natural calamities. Heatwaves can be recognised after a couple of days when temperatures persistently remain high, although they don't cause immediate visible impacts. However, extreme heat significantly affects public health, infrastructure, agriculture, and labour productivity, thereby impacting the economy. The cases of individuals seeking medical attention for heat-related illnesses or diseases indicate heat extremes' impact.
One positive side about heatwaves is that we know when it may happen. In Bangladesh, extreme heat events occur during the pre-monsoon season. Another issue is the increase in extreme heat events is almost certain and imminent. It is not like the hydrological hazards you mentioned. Their changes in Bangladesh are still very difficult to prove using existing statistics. The scope to know when it may occur enables us to address this hazard more effectively than other natural disasters.
Urban infrastructure development often ignores the environmental damage of an area. What is your take on it? How to balance urban development and environmental damage?
Urbanisation improves people's living standards and quality of life. There has been a rapid increase in urbanisation in the past few decades, which will continue in the future everywhere, including Bangladesh. Urban development reduces natural vegetation and increases impervious surfaces, resulting in higher land surface temperatures in urban areas compared to their surroundings, known as the urban heat island (UHI) effect. The increased impervious surface also reduces rainfall percolation to the subsurface and increases urban floods. But these negative impacts depend on sustainability in urban development. Unsustainable cities accelerate the UHI effect, exacerbating the environmental damage caused by urbanization. However, it is possible to mitigate these adverse effects by striking a balance between urban development and environmental protection. Urbanisation in Bangladesh was not controlled and sustainable. Our major cities are the most densely urbanised regions in the world. Improving the environment of such dense urbanised cities is very challenging. But many densely urbanised cities of the world are environmentally sustainable. This is possible by considering the environmental factors in all aspects of urban development and balancing urban development and environmental protection.
There has been talk about detecting and forecasting the urban heat island. Making people aware can be of help. But is there any way to actually get rid of those heat pockets?
Early warning of heat extremes is one of the most important measures to cope with their impacts. It is possible by tracking the relevant weather parameters and circulation patterns. We can also use the existing global forecasting system. But the problem is that the definition and characterisation of heatwaves or heat extremes in Bangladesh are not well-established. In reality, heatwaves and heat extremes lack a universally agreed-upon definition. Their identification relies on assessing the impact on human health, which can vary across different regions and change over time. Therefore, we must establish clear definitions for heatwaves or heat extremes to develop an effective early warning system.
Though early warning systems play a crucial role in mitigating the impacts of extreme heat, they alone cannot provide a comprehensive solution. A key aspect to address is reducing the UHI, particularly in heat-prone areas. Multiple factors contribute to heat intensity in urban pockets, such as street layout, building heights, density, spacing, surface characteristics, vegetation coverage, air pollution, and heat generated by air conditioning systems. It is possible to reduce heat effectively by modifying urban geometry, enhancing green spaces, increasing surface reflectivity (albedo), improving air quality, and promoting optimal air conditioning temperatures for cooling purposes.
Recently the matter of vegetation and tree plantation is being highlighted in Dhaka. But what about the other phenomena that contributes to extreme heat generation?
Anthropogenic heat flux significantly contributes to UHI. Studies showed that dense traffic during congestion leads to elevated temperatures in nearby areas. Additionally, the heat generated by air conditioning units contributes to further warming the surrounding environment. This creates a chain reaction where the increased temperatures increase the demand for cooling.
However, studies have also indicated that energy-efficient air conditioning systems and the use of electric or hybrid cars can significantly reduce the release of waste heat into the environment.
Despite adequate greenery, rural areas in Bangladesh are also suffering due to extreme heat…
The global temperature is on the rise due to the effects of global warming. As I mentioned earlier, the Earth's temperature has increased and become more unpredictable. This rise in mean temperature and variability has led to a greater frequency and severity of hot temperature extremes worldwide in recent years. Consequently, extreme heat can be felt everywhere. In one of my studies, I found an increase in high heat-stress days during the pre-monsoon season by 1 to 3 days per decade. This means that Bangladesh is now experiencing more extreme heat events compared to the past.
Moreover, temperatures can be exceptionally high in some years due to natural climate variability. This year, for example, some scientists attribute the elevated temperatures to the emergence of the El Niño weather pattern. Such phenomena can affect large areas, but they particularly exacerbate the situation in urban areas due to the existing UHI.
Do you believe overpopulation has anything to do with global warming? How is population contributing to extreme heat in Bangladesh?
Some try to establish a connection between overpopulation and global warming. However, I believe the impact of a higher or increasing population on global warming is minimal or even negligible. Instead, it is closely tied to economic development. A notable example is China, where the population growth rate has declined since the 1980s and is now approaching negative growth. But, greenhouse gas emissions in China have increased nearly fivefold during this period, primarily due to rapid economic growth.
The contribution of dense populations to UHI is also negligible. Factors such as paved surfaces with low albedo (reflectivity), limited vegetation, and building thermal mass play a more significant role in absorbing and storing heat, thus contributing to UHI. I have observed that the change in land surface temperature in the Rohingya camp in Ukhia, despite its high population density, is barely noticeable. This could possibly be attributed to the absence of buildings in that particular area.
India has recently introduced Heat Wave Action Plan in several of its cities including Ahmedabad. Can something similar to this help Bangladesh?
Not only Indian cities, other South Asian countries like Pakistan and cities in Southeast Asia have also adopted heat action plans to address and mitigate the impacts of extreme heat events. These plans involve establishing heatwave response committees comprising various government and non-governmental organizations. The cities are also actively strengthening their early warning systems, raising public awareness about heat-related risks, setting up cooling centers in heat-prone areas, and ensuring a consistent and reliable water supply during high-temperature months.
Furthermore, these cities have integrated heat mitigation strategies into their urban planning and development processes. These strategies include increasing green spaces, implementing cool roof initiatives, and enhancing natural ventilation in buildings. However, it is important to acknowledge that Dhaka, in particular, is a highly congested city, which poses challenges for the implementation of certain effective heat mitigation measures, such as creating larger water bodies or expanding green spaces. Therefore, careful examination of the effectiveness and feasibility of various strategies is necessary to identify suitable options for implementation in Dhaka's specific urban context.
Will you elaborate possible steps for sustainable temperature control in Bangladesh?
The effective control of global warming-induced temperature rise relies on successfully implementing commitments outlined in the Paris Agreement. However, it is within our capacity to manage and control the UHI effect. We may not have direct control over global warming-induced temperature changes, but we can certainly take measures to mitigate the conditions of high and extreme human heat stress. One of the most effective approaches is to increase the number of trees and shaded areas. Shade significantly reduces heat compared to direct sun exposure, thereby alleviating thermal stress and minimising heat-related injuries.
Implementing green roofs, cool roofs, natural ventilation systems in buildings, and strategically planting trees along roadsides, road dividers, and traffic islands are among the practical and easily implementable methods to combat the urban heat island effect. These measures contribute to creating a more sustainable and comfortable urban environment, mitigating the adverse impacts of excessive heat.
Thank you
You are welcome