DHAKA鈥橲 increasing heat is not just a result of global warming; it is also a consequence of poor urban planning. In the 1980s, wetlands covered 20 per cent of Dhaka. Today, only 2 per cent remain. A 2023 study by Bangladesh University of Engineering and Technology found that due to water body loss, Dhaka is heating up 60 per cent faster than the global average. This destruction has not only changed the landscape but has also disrupted the city鈥檚 microclimate, turning it into a heat island 鈥� a place where concrete structures trap heat, making life unbearable for residents.
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Science of natural cooling
WATER bodies act as nature鈥檚 air conditioners. Water has 4.75 times higher heat capacity than concrete, meaning it absorbs heat during the day and releases it slowly at night. A 2021 study by the University of California found that a 1-hectare pond can absorb 50-60 gigajoules of heat per day, reducing nighttime temperatures by 2-3掳C. This process helps maintain humidity and temperature balance in surrounding areas.
Additionally, waterbodies cool the air through evaporation. Each square meter of wetland evaporates 10-15 liters of water daily, which absorbs heat from the air. According to the Water Resources Research Institute, if Dhaka鈥檚 lost 320 hectares of wetlands still existed, they could have generated 3.2 billion liters of water vapour daily 鈥� lowering city temperatures by 4-5掳C. This evaporation process also helps break the urban heat dome, allowing natural air circulation.
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Water body loss and rising temperatures
FROM 1985 to 2023, Dhaka鈥檚 urbanisation surged, but water body conservation failed. The Environment and Social Development Organization reports that in 1985, Dhaka had 2,000 ponds and 4,200 hectares of wetlands. By 2023, only 29 ponds and 80 hectares remained.
This destruction is reflected in temperature trends. Between 1990 and 2023, Dhaka鈥檚 average temperature rose by 2.1掳C 鈥� 62 per cent higher than in rural areas (1.3掳C). Since 2010, the pace has accelerated. While wetland loss is happening at 8.5 per cent per year, temperatures are rising by 0.12掳C annually.
Local studies confirm this trend. A 2023 BUET thermal imaging study found that areas dominated by concrete, like Mirpur and Gulshan, are 5-7掳C hotter in summer than places with water bodies, like Dhanmondi Lake or Ramna Park. Also, night time temperatures in water body deprived areas are 4-5掳C higher, affecting sleep and overall health.
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Health and economy impact
THE loss of water bodies is not just increasing temperatures 鈥� it is harming Dhaka鈥檚 entire ecosystem.
In 2022, heatstroke caused 112 deaths in Dhaka, a 300 per cent increase from 2015 (28 deaths). According to icddr,b, cases of heat rash, dehydration and respiratory problems among children and the elderly rose by 40 per cent between 2010 and 2023 due to increased humidity and air pollution.
The demand for cooling systems has skyrocketed. According to the Power Development Board, Dhaka鈥檚 peak electricity demand in 2022 reached 3,800 megawatts 鈥� 60 per cent higher than in 2015. Rising air conditioning use has increased household and commercial electricity bills by 35 per cent in the past five years. Additionally, the government spent Tk 26,000 crore in 2022-23 on energy subsidies to meet the rising demand for imported fuels like diesel and furnace oil.
Extreme heat is affecting Dhaka鈥檚 workforce too. A World Bank report found that 40 per cent of outdoor workers 鈥� such as construction labourers, rickshaw pullers and farmers 鈥� lost 2-3 working hours per day due to heat stress. This is reducing gross domestic product by an estimated 1.2 per cent annually. Meanwhile, Dhaka鈥檚 residents are spending Tk 1,200 crore per year on heat-related illnesses, which now account for over 15 per cent of the city鈥檚 healthcare budget.
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Vicious cycle of heat
AS WATER bodies disappear, the need for artificial cooling rises, increasing energy consumption and carbon emissions, which further intensify the heat. According to the Department of Environment, Dhaka鈥檚 rivers and canals have lost 30 per cent of their water flow since 2010, increasing humidity by 18 per cent 鈥� pushing the heat index to dangerous level. Dhaka must prioritise water body restoration and urban greenery to break this cycle. Policies promoting wetland conservation, rooftop gardens and an improved public transport system can help cool the city. Without such sustainable actions, the rising heat will continue to threaten Dhaka鈥檚 health, economy and future.
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Arghya Protik Chowdhury is a student of environmental science at the听 Bangladesh University of Professionals.