Heatwave pattern is shifting to a ‘significant hazard’ for health, crops in Bangladesh


An analysis of data from the past few decades indicates that climate change is causing summer heatwaves at unexpected times and is affecting a wider range of areas, according to meteorologists. Hotspots are also growing larger.

Heatwaves have become a ‘significant hazard’ at the start of summer, but they are not occurring in the same areas and are not following the same pattern because of climate change, said meteorologist Dr Abdul Mannan. “We notice changes every year.”

For example, he said, heatwaves reached the southern district of Rangamati in the past two years. “This was not the case previously. Now there are changes to the heat maps in March and April. Temperatures are rising over time and more areas are becoming prone to heatwaves.”

According to the World Health Organization, a heatwave is generally defined as a period of at least five days where temperatures in an area are five degrees Celsius above the daily average. However, the specific parameters can vary according to country and region.

The Bangladesh Meteorological Department defines temperatures of 36 to 38 degrees Celsius as a mild heatwave, 38 to 40 as a moderate heatwave and temperatures above 40 degrees Celsius as an intense heatwave.

In mid-April this year, Khulna, Rajshahi and Dhaka divisions and their surrounding areas were experiencing mild to moderate heatwaves. Rain and storms brought some relief afterwards, but a moderate to intense heatwave returned at the end of the month.

Rajshahi has twice recorded temperatures of 41.2 degrees Celsius – the highest in the country so far this year. Eleven different locations across the country recorded temperatures between 36 to 40 degrees Celsius in the 30 days of April.

The 2019 Study on Heatwaves and Associated Large-Scale Circulation in Bangladesh gives a general idea of where the highest temperatures in the country were recorded between 1981 and 2016.

According to co-author Mohan Kumar Das, one of the longest heatwaves in the country was recorded in Chuadanga and Ishwardi in 1995, with 62 days of temperatures above 36 degrees Celsius.

Another heatwave lasted 60 days in Jashore in 2010, while a third in Rajshahi in 1994 dragged on for 55 days.

In 2014, a heatwave lasted for 79 days in Rajshahi, 51 in Mongla and 50 in Khulna.

The effects of a heatwave are felt less near the ocean and in coastal areas, Mannan said.

However, as the climate continues to change, temperatures are rising in districts such as Sylhet, Chattogram, and Rangamati, which is likely to have a long-term impact on the environment.

“Due to its geographical location, the western part of our country is prone to heatwaves. In addition, atmospheric conditions cause some other areas to also experience heatwaves,” said Mannan.

“Recently, we have seen heatwaves in the southern regions of the country in addition to the west. Even Rangamati saw heatwaves last year.”

Rangpur was more prone to heatwaves, but the area has seen a gradual decline in such occurrences, Dr Mannan said. Temperatures in Rangpur did not rise too much this year.

Rajshahi, Khulna, Barishal, Chattogram and Dhaka divisions are now experiencing heatwaves. In the past, there were no heatwaves in Sylhet. But they have experienced them last year and this year.”

In the long-term forecast for May, the Met Office said it expects an intense heatwave in the western part of the country, and one to two mild or moderate heatwaves in the rest of the country.

Dr Samarendra Karmakar, former chairman of the National Oceanographic and Maritime Institute, said Bangladesh historically experienced more intense heat in May. The highest temperature on record – 45.1 degrees Celsius – was recorded in May 1972.

“We have seen that when average temperatures are high in April, the highest temperatures are recorded in May. May has just started. We will see what heatwaves are to come this year.”


Parts of India and Pakistan have registered record high temperatures this year, putting millions of people at risk in both countries.

On Apr 12, New Delhi registered a high of 42.6 degrees Celsius, the highest April temperature in 72 years. Pakistan’s Sindh province recorded highs of 47 degrees Celsius at the start of May.

Meteorologists say that the effects of heatwaves in India are felt in Bangladesh. The effects of the climate change crisis can be felt across the Indian subcontinent.

“Cyclones start in one area and then move to others, so do heatwaves,” said Mannan. “A heatwave starts in India’s Rajasthan and then moves across Uttar Pradesh to Bihar and then West Bengal. Its effects can be felt in Bangladesh as well.”

Part of a heatwave that starts in India can reach or extend into Bangladesh and then spread across the country, he said.

However, it should be of some comfort to Bangladeshis that these heatwaves reduce in intensity before they reach the country.

Samarendra, who is also a former director of the Bangladesh Meteorological Department, said the heat from intense heatwaves in India gradually enters Bangladesh through the Jashore-Kushtia-Satkhira region. This is why this area generally has higher temperatures. By the time these heatwaves spread to Bangladesh, the temperatures drop by 8-10 degrees Celsius.

The flow of heat is required for Bangladesh’s weather cycle in order to prevent delays in the monsoon season, the meteorologist said.

“But, if India’s heatwaves are on the rise, the effect will also be felt here. The heatwave in India and Pakistan is part of a weather system that will affect us as well.”


Heatwaves will slowly become a significant concern for Bangladesh as floods are, according to Mohan Kumar, a researcher of numerical weather prediction modelling and meteorology.

“Our research shows that Dhaka and other central areas of the country are now experiencing heatwaves. People, farmers and fauna are suffering the most. Private and public initiatives are necessary to supply clean water, plant more trees and provide rest areas in the shade.”

Rice grows best at temperatures between 25 and 35 degrees Celsius. Higher temperatures are detrimental to rice, stunting growth and reducing grain yield.

The temperatures in April and May, which regularly reach or exceed 35 degrees Celsius, make rice farming untenable.

Last April, similar temperatures caused heat shocks in the northeastern wetland regions of Bangladesh, ruining crops on nearly 50,000 hectares of land.

Dr ABM Arif Hasan Khan Robin, a professor of genetics and plant breeding at Bangladesh Agricultural University, said that work is underway to develop rice varieties that can withstand high temperatures because of such adverse weather conditions. These new varieties will be available in the next few years.

Temperatures above 36 degrees Celsius severely damage the flowering of rice paddy, and so farmers need to know when heatwaves are coming, he said.

It is possible to reduce heat damage to paddy during times of high temperature with the use of a special spray, Dr Arif said.

Dr Md Shahjahan Kabir, the director general of the Bangladesh Rice Research Institute, says a variety of rice that is resistant to high temperatures is being tested for its regional yield. If the yield and other characteristics of the rice prove acceptable, the variety will be submitted to the National Seed Board for approval.

If it is approved, the variety will be able to flower and yield at temperatures above 35 degrees Celsius, he said.

RISKS TO PUBLIC HEALTH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Day labourers suffer the most from the intense heat. Experts urge the provision of clean water and shaded rest areas to help them cope with scorching heat.

Many people are at risk of heatstroke if they venture outside in the intense heat, said Dr MH Chowdhury Lelin, a public health specialist.

When exposed to intense sunlight for an extended period, the body loses its ability to regulate heat, causing temperatures to rise, similar to when experiencing a fever. Excess sweat also causes the body to lose salt and water.

“Dehydration and lack of salt destroy the balance of electrolytes in the body. When this happens, people can lose consciousness and suffer heatstroke.”

Children, the elderly, those who are suffering from a major disease, and those with lower immunity are at greater risk of heatstroke, the doctor said.

Anyone suffering from serious dehydration or salt imbalance in the body must seek medical help immediately, said Dr Lelin, who is also the director of Health and Hope Specialised Hospital. They are at greater risk of contracting viral diseases and suffering from diarrhoea and food poisoning.