Bangladesh has made remarkable progress in reducing deaths from floods and cyclones through decades of investment in disaster preparedness. Today, however, the country faces a different kind of climate emergency. Extreme heat is emerging as one of the greatest threats to public health, productivity, and sustainable development, yet it remains one of the least recognised climate risks. This hazard is steadily tightening its grip on the country, rarely destroying homes overnight, yet quietly threatening almost every aspect of daily life.

Temperatures are rising under global warming

Climate scientists warn that these events are not isolated anomalies but part of a long-term warming trend driven by global climate change. Rising greenhouse gas concentrations are increasing both average temperatures and the likelihood of extreme heat events worldwide, and Bangladesh is among the countries expected to experience particularly severe consequences due to its tropical climate, dense population, and high socioeconomic vulnerability. In 2025, the global average temperature was 1.47°C above pre-industrial levels, making it the third-warmest year on record, according to Copernicus Climate data.

Extreme heat is emerging as one of the greatest threats to public health, quietly threatening almost every aspect of daily life. Photo: Rashed Shumon/ Star

In a recent BUET study, the mean annual temperature in Bangladesh is projected to rise by approximately 1.4°C to 4.8°C by the end of this century, depending on future global emissions. Such warming fundamentally changes the probability of extreme heat, making intense heatwaves more frequent, longer-lasting, and more severe than those experienced historically.

Increasing frequency of heat days

Evidence already suggests that this transition has begun. Analysis of more than five decades of meteorological records indicates that the frequency of heat days has increased significantly during the last decade, with Dhaka alone experiencing several moderate heatwaves over the past half-century. Climate projections consistently indicate that future summers will become increasingly dominated by prolonged periods of dangerous heat, affecting larger parts of the country and exposing millions more people to potentially hazardous conditions.

Bangladesh's humid tropical climate makes extreme heat considerably more dangerous than the thermometer may suggest.

Yet temperature alone does not tell the whole story. Bangladesh's humid tropical climate makes extreme heat considerably more dangerous than the thermometer may suggest. Human bodies rely on the evaporation of sweat to regulate internal temperature. When humidity is high, sweat evaporates much more slowly, reducing the body's natural cooling mechanism. As a result, people experience substantially greater physiological stress even when air temperatures are not at record-breaking levels. This combined effect of temperature and humidity is commonly measured using the Heat Index, often referred to as the "feels-like" temperature or apparent temperature.

Mortality, illness and impact on livelihood

Studies indicate that humid heatwaves, during which both daytime and night-time temperatures remain exceptionally high while humidity is elevated, pose greater health risks than dry heat alone. Particularly concerning are nights that remain unusually warm. Normally, cooler night-time temperatures allow the human body to recover from daytime heat exposure. When nights remain hot, recovery becomes impossible, leading to cumulative heat stress over several consecutive days and substantially increasing the risks of illness and mortality. Bangladesh has already witnessed the human cost of such events.

One study found that mortality increased by approximately 22% during day-and-night heatwaves, while humid heatwaves increased mortality by around 24%, highlighting the deadly combination of persistent heat and humidity. Globally, extreme temperature hazards claimed more than 7,000 lives and affected over 8.7 million people between 2005 and 2014, underscoring that heat is no longer merely an environmental issue but an increasingly significant public health emergency.

Older adults account for nearly 80–90% of excess heat-related mortality, while infants, pregnant women, outdoor labourers, people with chronic illnesses, and low-income households also face elevated risks.

Certain groups bear a disproportionate share of this burden. Older adults account for nearly 80–90% of excess heat-related mortality, while infants, pregnant women, outdoor labourers, people with chronic illnesses, and low-income households also face elevated risks. For many of these populations, avoiding exposure is simply not an option. Daily income often depends on working outdoors, regardless of the temperature. The dangers posed by climate change are further intensified by the way cities in Bangladesh are expanding.

Urban heat island effects

Rapid urbanisation has transformed large areas of Dhaka, Gazipur, Narayanganj, Chattogram, and other metropolitan centres into landscapes dominated by concrete, asphalt, steel, and glass. Green spaces continue to disappear, wetlands are being filled, water bodies are shrinking, and densely packed buildings restrict natural airflow. Together, these changes create the Urban Heat Island (UHI) effect, whereby cities remain significantly warmer than their surrounding rural areas. Urban surfaces absorb large amounts of solar radiation during the day and slowly release the stored heat throughout the night. Consequently, city residents often experience elevated night-time temperatures that prevent the body from recovering after prolonged daytime exposure. In many neighbourhoods, temperatures remain high well after sunset, extending heat stress well beyond daylight hours.

This phenomenon is particularly concerning because the urban population of Bangladesh continues to grow rapidly. Millions now live in densely populated neighbourhoods where limited vegetation, traffic congestion, industrial activities, and inadequate ventilation further compound heat exposure. As climate change raises regional temperatures, urban heat islands amplify these increases locally, creating conditions that are considerably hotter than those in surrounding rural environments. The consequences extend well beyond discomfort.

Impacts on water and energy

Higher urban temperatures increase electricity demand as households and businesses rely more heavily on fans and air conditioning. Peak electricity demand during hot summer afternoons already places enormous pressure on Bangladesh's power system. Rising temperatures are expected to further increase cooling demand while simultaneously reducing the efficiency of power plants, accelerating transformer ageing, increasing transmission losses, and making blackouts more likely unless infrastructure is upgraded.

Water systems face similar challenges. Hotter weather substantially increases domestic water consumption, particularly during the pre-monsoon season. As temperatures continue to rise, urban water demand is projected to increase even further, placing additional strain on already stressed water supply networks. This creates a dangerous cycle: hotter cities require more electricity and more water precisely when these essential services become increasingly difficult to provide.

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The dense urban landscape of Dhaka, dominated by concrete and lacking sufficient green spaces, increasingly traps heat, transforming the capital into a rapidly warming urban heat island. Photo: Anisur Rahman/ Star

Impacts on infrastructure

Heat also affects the infrastructure itself. Roads constructed for historical climate conditions may soften and deform under prolonged periods of high temperatures. Railway tracks become more susceptible to thermal expansion and buckling. Building materials deteriorate more rapidly under repeated heat exposure, while cooling costs for offices, hospitals, schools, and industries continue to rise. Infrastructure that was designed decades ago is increasingly being asked to perform under climatic conditions for which it was never engineered. Extreme heat is often perceived as a public health issue, but its consequences extend far beyond hospitals.

Impacts on workers and productivity

Extreme heat is quietly eroding productivity, slowing economic growth, and widening social inequalities in Bangladesh. The country's economy depends heavily on outdoor and labour-intensive sectors, including agriculture, construction, transport, fisheries, brick kilns, and manufacturing, where work cannot simply stop when temperatures soar. Heat stress causes fatigue, dehydration, reduced concentration, slower reaction times, and, in severe cases, heat exhaustion or heat stroke. As a result, workers slow down, take more breaks, or stop working altogether, reducing both labour supply through absenteeism and labour efficiency through presenteeism.

The economic costs are substantial. Globally, climate-induced heat stress is projected to reduce GDP by 0.5% under low-emission scenarios and by up to 1.4% under high-emission scenarios by the end of the century. When health impacts and supply-chain disruptions are included, total economic losses could reach 0.6–4.6% of global GDP by 2060, while heat-related labour productivity losses alone may amount to 0.31–2.6% of global GDP by 2100. Between 1992 and 2013, anthropogenic extreme heat is estimated to have reduced global economic output by US$16–50 trillion, with low-income tropical countries suffering annual income losses equivalent to about 8% of GDP per capita, compared with 3.5% in wealthier regions.

Bangladesh is already experiencing these impacts. A recent survey across major cities found that heat exposure costs workers an average of US$281 per person annually through reduced productivity. Illness and absenteeism account for around US$144 per worker each year, while reduced on-the-job efficiency adds another US$225. The losses are greatest among workers in agriculture, construction, fisheries, healthcare, hospitality, and other occupations requiring prolonged outdoor work.

Construction workers are among the most vulnerable, often working in direct sunlight with limited access to shade, drinking water, or cooling facilities. Many continue working despite dangerous conditions because daily wages determine daily survival. Factory workers in Bangladesh's ready-made garment sector also face increasing heat stress, as crowded industrial buildings with poor ventilation reduce productivity and threaten one of the country's most important export industries. Yet occupational standards still provide limited guidance on workplace temperatures, mandatory rest breaks, or work adjustments during extreme heat.

The impacts extend beyond the workforce. Research shows that when daily temperatures exceed 36°C, school attendance declines while child labour increases, particularly among girls, who often shoulder greater household responsibilities during heatwaves. These disruptions, combined with falling household incomes and rising health burdens, risk reinforcing long-term cycles of poverty.

Impacts on agriculture and food security

Rising temperatures affect crop development, increase evapotranspiration, intensify irrigation demand, and expose crops to damaging heat stress during sensitive growth stages. Rice, the staple food of Bangladesh, is particularly vulnerable when temperatures exceed critical thresholds. While moderate increases in minimum temperatures have benefited yields in some regions, temperatures above 35°C have been shown to reduce rice production, especially in the north-western districts of the country.

Temperature anomalies have explained substantial variations in Aus, Aman, and Boro rice yields in recent decades, illustrating how increasingly frequent heat extremes are becoming an important determinant of agricultural productivity. Higher temperatures also intensify drought conditions, increase dependence on groundwater irrigation, accelerate saltwater intrusion into coastal aquifers, and reduce the environmental suitability of crops such as wheat and dry-season rice. Rising sea-surface temperatures in the Bay of Bengal and increasing freshwater scarcity further threaten fisheries and aquatic ecosystems that support millions of livelihoods.

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A truck-mounted cannon is spraying water on vehicles on Airport Road in the Banani area. Dhaka North City Corporation started using water cannons to spray water in its areas to prevent air pollution and keep the city cool during the heatwave. Photo: Palash Khan/ Star

Preparing for a hotter future

Extreme heat is no longer a distant climate threat, as it is already reshaping lives, livelihoods, and the economy of Bangladesh. Just as the country has become a global leader in reducing disaster risks from floods and cyclones, it must now prepare for a hotter future through heat action plans, climate-resilient urban planning, worker protection, heat-resilient infrastructure, stronger early warning systems, and other targeted adaptation measures. Recognising extreme heat as a national development challenge, rather than merely a seasonal inconvenience, will be essential to protecting public health, sustaining economic growth, safeguarding livelihoods, and building a more climate-resilient Bangladesh.

A.K.M. Saiful Islam is a professor, and Fariha Islam Mou is a lecturer at the Institute of Water and Flood Management (IWFM), Bangladesh University of Engineering and Technology (BUET).

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