Dhaka ranks worst in dwellers’ exposure to heat: Study

Dhaka is the worst city in the world in terms of dwellers’ exposure to extreme heat caused by rapid population growth and global warming that aggravates health problems, a study says.

Between 1983 and 2016, Dhaka’s population rose dramatically and the city experienced an increase of 575 million person-days of extreme heat, according to the study titled “Global Urban Population Exposure to Extreme Heat”, published in the Proceedings of the National Academy of Sciences, better known as PNAS journal.

The increase in extreme heat in Dhaka is largely attributable to its population soaring from around four million in 1983 to around 22 million today.

The researchers said the patterns they found in South Asia and Africa “may crucially limit the urban poor’s ability to realise the economic gains associated with urbanisation.”

They added that sufficient investment, humanitarian intervention, and government support would be needed to counteract the negative impact.

“The exposure to extreme heat increases morbidity and mortality. It impacts people’s ability to work and results in lower economic output. It exacerbates pre-existing health conditions,” the study read.

In recent decades, hundreds of millions of people have moved from rural areas to cities where temperatures are generally higher because of surfaces, such as asphalt, which trap heat and a lack of vegetation.

The scientists studied the maximum daily heat and humidity in more than 13,000 cities from 1983 to 2016 and then compared weather data with statistics on the cities’ population over the same 33-year period.

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.

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, 17 per cent experienced an additional month of extreme-heat days during the period.

The lead author of the study Cascade Tuholske of Columbia University’s Earth Institute said, “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?”

Using the “wet-bulb globe temperature” scale, a measure that takes into account heat and humidity, the researchers defined extreme heat as 30 degrees Celsius.

They calculated the number of days of extreme heat in a particular year by the population of the city that year to come up with a definition called person-days.

They found that the number of person-days to which city dwellers were exposed went from 40 billion per year in 1983 to 119 billion in 2016.