These areas have been termed 'heat islands', which are defined as urbanised areas that experience higher temperatures than their outlying areas.
The findings were made in a report published in September titled 'Feasibility Study on Heatwave in Dhaka'. The study was conducted jointly by Bangladesh Meteorological Department, Bangladesh Red Crescent Society and German Red Cross.
One of the key objectives of the study was to identify the trigger and thresholds of heatwaves along with their impacts, especially on the vulnerable population of Dhaka city and propose early actions to minimise them.
Researchers identified the hotspots, using the Geographic Information System (GIS) software which is designed to analyse geographic and spatial data, according to Mohammad Shahjahan Shaju, assistant director of Bangladesh Red Crescent Society.
“This was a pilot study covering Dhaka through which the heat islands in the capital were identified amid a growing trend of scorching heat.”
DHAKA’S HEAT ISLANDS
The neighbourhoods marked as heat islands are Badda, Gulshan, Kamrangirchar, Mirpur, Gabtoli, Goran, Basabo, Tongi, Shaheednagar, Babubazar, Postogola, Jurain, Hazaribagh, Jatrabari, Sayedabad, Kurmitola, Azampur, Uttara, Kamarpara, Mohammadia Housing, Adabor, Farmgate, Tejkunipara, Nakhalpara and Mohakhali.
Heatwaves have been quite prominent in the capital in recent years, experts said. The mercury hovers between 29 degrees Celsius and 34.5 degrees Celsius on average in Dhaka’s heat islands, leaving them in the grip of a heatwave.
A heatwave typically occurs when a vast area experiences a high temperature for three consecutive days.
A temperature between 36-38 degrees Celsius signified a mild heatwave, 38-40 degrees Celsius a moderate heatwave, while the level above 40 degrees Celsius is considered an extreme heatwave.
“Usually, a temperature up to 36 degrees Celsius is reasonable; but it becomes intolerable when it goes beyond that. We recommend early action when the mercury crosses 38 degrees Celsius,” said Shahjahan.
Rising temperature is a global phenomenon and Bangladesh is no exception.
That level of warming, measured against preindustrial levels, is likely to increase the frequency of deadly heatwaves and threaten coastal cities with rising sea levels, the country-by-country analysis concluded.
Senior Meteorologist Dr Abdul Mannan believes Dhaka will continue to experience heatwaves and the temperature will become unbearable in some neighbourhoods that are swarming with high-rise buildings, factories or dense populations.
“Other cities like Khulna, Barishal and Rajshahi are gradually becoming vulnerable to extreme heat,” Mannan said.
SWELTERING HEAT: PAST AND PRESENT
>> The mercury rose to 41.2 degrees Celsius in Jashore on Apr 24, the highest recorded this year. Dhaka recorded its highest temperature at 39.5 degrees Celsius.
>> In the second half of April, the temperature in most parts of Bangladesh ranged from 36 degrees Celsius to 40 degrees Celsius.
>> A 'heat shock' swept over vast swaths of the country, including Netrokona, Madan, Khaliajuri, Kendua, Kishoreganj's Nikli and Karimganj in April.
>> In 2014, the highest temperature in Bangladesh was recorded at 42 degrees Celsius in Chuadanga, while the mercury peaked at 40 degrees Celsius in Dhaka.
>> Over the past two decades, Jashore recorded the highest temperature in Bangladesh, at 42.2 degrees Celsius. Before that, the mercury climbed to 43 degrees Celsius in 1995.
>> As of now, the highest temperature on record in Bangladesh is 45.1 degrees Celsius logged on May 18, 1972.
HEATWAVES INTENSIFYING, EXPANDING
"We have seen an uptick in lightning cases recently. Also, there's a rising trend of heat waves sweeping over the country, mostly in July. The time and space are changing [for these natural phenomena],” he said.
"For the last few years, heatwaves didn't dominate the pre-monsoon period. This year, a good number of them swept through the country, especially from March to May. At least four of them were strong and lasted for a long time.”
Dhaka and other densely-populated major cities like Khulna, Barishal and Rajshahi are gradually becoming prone to heatwaves, according to Mannan.
"Sylhet was among the places that would never experience heat waves due to the local weather and heavy rains. But a recent analysis showed that Sylhet is also becoming vulnerable to heatwaves," the meteorologist said.
This year's heatwaves expanded up to Sylhet. Chattogram never experienced heatwaves in the past. This year, areas from Sitakunda to Rangamati were affected. The mercury rose to 39.3 degrees Celsius."
FORECAST AND AWARENESS
Mannan stressed the need for initiatives that address the issue of heatwaves.
"Many people have died in Canada this year due to a heatwave. People face a lot of hurdles, especially the day labourers or members of lower-income groups, who could lose their earnings. Elderly people fall sick. Some of them suffer from diarrhoea or other diseases caused by lack of nutritious food.”
It is necessary to forecast heatwaves, even though it is “an unusual phenomenon” in order to reduce the plight of the vulnerable people, he said.
“We have contacted the Directorate General of Health Services. Many of us do not realise why people in Dhaka are falling ill frequently," said Shahjahan Shaju, assistant director of Bangladesh Red Crescent Society.
"Sometimes they have a heat stroke. We need to create awareness on how to address such issues.”