Hotter, drier summers may be new norm

Expressing concern over the record temperature rise in April and May in Bangladesh, experts have warned that this can become the new normal for the country.

According to Bangladesh Meteorological Department (BMD), heatwaves swept over different parts of the country for 24 days in April and 22 days in May this year.

In 2018, heatwaves lasted 10 days in April and eight days in May.

These two months also witnessed very low rainfall this year compared to the average rainfall during the same period over the last 30 years.

The 30-year average rainfall for April was 134 millimetres while the figure was 284 millimetres for May. But this year, the rainfall was 66.4 percent less in April and 44.1 percent less in May than the 30-year average, according to BMD data.

"This year's weather pattern is very unusual. The frequency of heatwaves is increasing, the areas affected are widening gradually, and the temperature is also on the rise," Md Monowar Hossain, a meteorologist at the BMD, told The Daily Star yesterday.

Meteorologists said this change in weather conditions has become a new weather phenomenon in the country.

According to the World Health Organisation, 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.

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.

Experts say that erratic rainfall, high temperatures, extensive areas under heatwaves and their frequency are the new worries for Bangladesh, one of the worst victims of global warming.

"Increased human activities both at the global, regional and local levels are responsible for the warming of the climate. In Bangladesh, the heatwave magnitude and frequency situation would become worse in future, especially in cities," Ashraf Dewan, professor at the School of Earth and Planetary Sciences of Curtin University, Australia said.

In Southeast Asia, April and May are usually the warmest months of the year.

In a recent report from the World Weather Attribution (WWA), an international coalition of scientists said the April heatwave in Southeast Asia was a once-in-200-year event that would have been "virtually impossible" without the human-caused climate change.

Dhaka experienced 40.6°C on April 16, the highest in the capital in 58 years.

Towhida Rashid, a professor and the founding chairperson of the Department of Meteorology at Dhaka University, said the greenhouse gas layer is getting thicker in the atmosphere and the temperature is on the rise both over land and ocean.

"As we are entering into the El Niño phase, the dry spell will continue for a few more years. So, the intensity and the duration of heatwaves will continue to increase in Bangladesh. We have to be adaptive to this weather pattern," she said.

El Niño is a unique state of the global climate, which warms the surface waters of the equatorial Pacific Ocean, affecting the ionosphere and surrounding climate.