Sudden temperature drops in winter, sweltering and frequent heatwaves in summer, poor rainfall during monsoon, and four cyclones marked this year, and the experts blame it on climate change.

Heatwaves swept over the country for 62 days -- 24 days in April, 22 days in May, and 16 days in June, according to the Bangladesh Meteorological Department data.

Dhaka recorded the highest temperature in 58 years, 40.6 degrees Celsius, on April 16. The very next day, the people of Ishwardi endured a temperature of 43 degrees Celsius, the highest in the country this year.

The country witnessed the effects of four cyclones -- Mocha in May, Hamoon in October, Midhili in November, and Michaung in December.

Experts said erratic weather patterns have become a major concern for Bangladesh, one of the worst climate change-affected countries.

"Extremes are changing in frequency and intensity due to global warming," said Prof AKM Saiful Islam, one of the lead authors of the Intergovernmental Panel on Climate Change assessment report.

"Although it is difficult to link individual extremes or with one year's data to long-term climate change, it is evident that we have seen extreme and rare events in this decade as an early sign of climate change," he told The Daily Star.

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

Bazlur Rashid Khan, a meteorologist at the BMD, said, "We observed that temperatures were above 36 degrees Celsius almost nationwide for more than 15 days at a stretch. We also saw that in winter temperature drops were sudden and by a large margin. This has a multifaceted impact on lives and livelihoods."

Ashraf Dewan, a professor at the School of Earth and Planetary Sciences of Curtin University, Australia, said global climatic change and local changes in climate caused by intense human activities are triggering unusual weather patterns in many places of the world, including in Bangladesh.

"If local level anthropogenic activities, like land transformations, cannot be controlled, weather extremes such as heatwaves and little monsoon rain will continue to aggravate in the coming days," he said.

He said land-use changes at the local level have a significant impact on land-atmosphere interactions, resulting in unusual weather patterns.

Mohan Kumar Das, executive director at the National Oceanographic and Maritime Institute, said the unusual weather patterns observed in Bangladesh and in the Bay of Bengal, characterised by prolonged heatwaves, deficient rainfall, and increased cyclonic activity, can be attributed to a combination of natural and anthropogenic factors.

He said global climate change, primarily driven by rising greenhouse gas emissions, influences the overall climate system, leading to alterations in temperature and precipitation patterns.

"The Bay of Bengal's oceanic conditions, including sea surface temperature fluctuations and atmospheric circulation changes, play a pivotal role in shaping the region's climate," Mohan said.

The periodic El Nino and La Nina events in the Pacific Ocean contribute to variability in weather patterns, impacting heatwaves, rainfall, and cyclone intensity. Local factors such as land use changes, air pollution, and geographic features amplify these effects, he 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.

M Asaduzzaman, former research director at the Bangladesh Institute of Development Studies, said phenological changes caused by unusual weather patterns were evident and they were creating a burden for farmers.

"The weather pattern is changing and so is agriculture. To have a deeper understanding of this change, we need a more evidence-based information," he said.

Several experts believe that unusual weather patterns have an impact on agriculture and healthcare.