Dhaka worst-affected city in world by urban heat: Study

Amid a pursuit for high economic growth and improving standards of living, Bangladesh now faces a new threat: deadly urban heat.

According to a study by the Proceedings of the National Academy of Sciences (PNAS) of the United States of America journal, Dhaka is the worst-affected city in the world in terms of deadly urban heat.

In the study, titled "Global urban population exposure to extreme heat", published in the PNAS journal, it was shown that exposure to deadly urban heat had tripled since the 1980s, and now it affected nearly a quarter of the world's population.

"This has broad effects," said Cascade Tuholske, lead author of the study and a postdoctoral researcher at Columbia University's Earth Institute.

"It increases morbidity and mortality. It impacts people's ability to work, and results in lower economic output. It exacerbates pre-existing health conditions," he added.

Between 1983 and 2016, Dhaka's population rose dramatically, with the city experiencing an increase of 575 million person-days of extreme heat.

Other cities that underwent rapid population growth include Shanghai and Guangzhou in China, Yangon in Myanmar, Bangkok in Thailand and Dubai in the United Arab Emirates.

Scientists have put the worrying trend down to the combination of rising temperatures and growing number of people living in urban areas, and warned of its potentially fatal impact.

The study found that the number of person-days -- the cumulative population exposed to cumulative heat in a given year for a particular place -- soared from 40 billion a year in 1983 to 119 billion in 2016, representing a threefold increase.

In 2016, 1.7 billion people were subjected to extreme heat conditions on multiple days.

Although it varied between cities and regions, scientists attributed two-thirds of the overall rise in exposure to increased urban populations and a third of it to global heating.

Cities that had at least half of their heat exposure caused by global heating include Baghdad in Iraq, Cairo in Egypt and Mumbai in India.

Of the cities studied in the research, 17% experienced an additional month of extreme-heat days during the period, which spanned just over three decades.

"A lot of these cities show the pattern of how human civilisation has evolved over the past 15,000 years. The Nile, the Tigris-Euphrates, the Ganges … there is a pattern to the places where we wanted to be. Now, those areas may become uninhabitable. Are people really going to want to live there?" Tuholske said.

A Brazilian study analysing the impact of forest loss on human health found that by 2100 as many as 12 million Brazilians could be exposed to extreme risk of heat stress as a result of large-scale deforestation of the Amazon and climate change.

According to Global Forest Watch, an online platform that provides data and tools for monitoring forests, in 2010, Bangladesh had 2.22 million hectares of tree cover, extending over 16% of its land area. In 2020, it lost 21.5 thousand of hectares of tree cover, equivalent to 11.6 metric tonnes of carbon emissions.

Meanwhile, a European research has predicted the economic costs of heatwaves could increase by nearly five times by 2060.

This wasn't, however, the first time Dhaka listed its name in a worrying list.

The Global Liveability Index 2021 ranked Bangladesh's capital as the fourth least liveable city in the world.

In April of this year, the densely populated capital of Bangladesh had topped the list of world cities with the worst air quality.

The rankings, however, are not entirely due to failures in Bangladesh's governance and policies.

One of the reasons for Dhaka's ranking in the PNAS ranking in terms of urban heat was global climate change.

One of the biggest reasons for climate change is the emission of greenhouses gases.

According to the World Resources Institute, the top three greenhouse gas emitters  -- China, the European Union and the United States -- contribute 41.5% of total global emissions, while the bottom 100 countries only account for only 3.6%/

While Dhaka remains affected by the emissions of other countries, it does not have the ability to change much on a ground level.

The study used infrared satellite imagery and maximum daily heat and humidity readings from more than 13,000 cities from 1983 to 2016 to determine the number of people exposed to the days a year that exceeded 30C (86F) on the wet-bulb globe temperature scale, it also took into account the multiplier effect of high humidity in an area. They matched the findings with the cities' populations over the same period, reports the Guardian.