Unusual summer this year

Summers in Bangladesh are usually unforgiving as the mercury keeps on rising throughout the season, but not this time. This year, the summer is unusual, with relentless rains and thunderstorms dominating most part of the season from March to April.

Both frequency and persistence of rain and lightning strikes are more than usual this time, said Dr Samarendra Karmaker, former director of Bangladesh Meteorological Department.

“From April, I do not think there has been a day when it did not rain. It stops for a day or two and is back again. Therefore, it can be said without a doubt that frequency of rain has increased,” says Samarendra.

Also owing to the frequent and persistent rains, there has been no heat wave this season, he says.

“Rain and lightning strikes are more frequent this time. Our paddy fields are in vast empty expanse, meaning we have no place to take shelter if lightning strikes. And this is causing difficulty for us to even harvest our crop,” said Abdul Monem, 45, of Tahirpur, Tanguar Haor in Sunamganj district.

Recent data shows that around 70 people were killed in lightning strikes in different parts of the country between March and April.

“You will notice that the victims of lightning strikes are mostly farmers and this makes sense because lightning strikes the highest object first,” Dr Samarendra said.  

In the harvesting season, this makes farmers easy targets as they work on open fields.

This is because thirty or forty years ago, there were only two paddy harvests -- Aush and Aman -- but now farmers also plant Boro paddy that ripens around the end of April and beginning of May, which is also Kalbaishakhi season.

Dr Samarendra explains the persisting and frequent rainfall in scientific terms: “There is an easterly low pressure which comes through the Indian southern peninsula and moves up to the land through the north and north-east. There is nothing unusual about that. What is unusual is, although this normally lasts for four to five days, this year the system is persisting. That is because the sub-tropical high pressure over the Bay of Bengal is weak this time. Had it been stronger, it would have helped move the easterly low-pressure towards the Arabian Sea.”

The easterly low pressure is now passing through the Khulna region and entering Bangladesh. Along with that there is a westerly low pressure system that is persisting and is passing through Uttar Pradesh, Bihar and West Bengal.

The conjugation of both the systems near Bangladesh is resulting in higher frequency of rains and thunderstorms.

Asked why these systems are persisting, Samarendra said, “The reason is practically unknown. However, it could be that there is a change in global circulation pattern.”

Questioned whether there is any link between frequent thunderstorms and rain, Samarendra said “There is no established link yet between frequent thunderstorms, rain and climate change.”

Understanding Easterly waves

When we hear "wave", we usually picture a wave crashing against the shore of a beach. Now, imagine that wave being invisible and in the upper atmosphere and we have got the gist of what a meteorological tropical wave is.

Also called easterly wave, invest, or tropical disturbance, a tropical wave is generally a slow-moving disturbance that's embedded in the easterly trade winds.

The westerlies, anti-trades, or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude.

Extreme weather patterns the new normal?

Are extreme weather patterns becoming the norm owing to climate change? The question keeps popping up, every year, as new and extreme weather events continue to affect the country.

According to rainfall and temperature data recorded at seventeen meteorological stations over the time period 1958-2007, there was an increase in annual rainfall of Bangladesh at a rate of 5.53 mm/year and pre-monsoon rainfall at a rate of 2.47 mm/year, according to a study on recent trends in the climate of Bangladesh by Shamsuddin Shahid of Department of Geology, University of Malaya.

Quoting a positive correlation between the sea surface temperature in the Bay of Bengal and the rainfall of Bangladesh, Shahid in his study said, “It can be remarked that increase in sea surface temperature of Bay of Bengal might be the cause of increased precipitation in Bangladesh. It is not possible to come to a decision about global climate change impact on rainfall and temperature of Bangladesh by analysing the data presented in this paper.”

Bangladesh is among one of the most vulnerable countries to climate change and also one of the most disaster prone countries in the world, according to Intergovernmental Panel on Climate Change.

As the planet warms and sea-level rises, it is likely that typhoons, especially in South and South-east Asia, will get stronger, according to an article published by The Guardian in 2016.

Storms feed off of latent heat, which is why scientists think global warming is strengthening storms.

The destructive power of typhoons that wreak havoc across China, Japan, Korea and the Philippines has intensified by 50% in the past 40 years due to warming seas, reports an article published by The Guardian in 2016.

“The researchers warn that global warming will lead giant storms to become even stronger in the future,” read the article titled ‘Asian typhoons becoming more intense, study finds’.

According to the Guardian report, Prof Wei Mei, at the University of North Carolina at Chapel Hill, said it is clear that the future global warming, as projected by the UN’s Intergovernmental Panel on Climate Change, would heat the oceans in the region and lead to even more intense typhoons.