There have been marked changes in Bangladesh’s rainfall patterns with increasing rains occurring during the spring and less than the usual precipitations occurring in the monsoon months.
In the parlance of the Met Office, Bangladesh has four and not six seasons.
The four seasons include pre-monsoon, monsoon, post-monsoon and winter.
This year July, which used to be the wettest month with average rainfall of 523 mm, got 16 per cent less of rainfall in the first 24 days, according to the Met Office.
In June, the second wettest month, this year the Met Office recorded 455 mm of rainfall which was four mm less than the normal.
But the scenario changed during the pre-monsoon season, spanning March and May.
Spring, not found in Met Office literature, spans mid-February and mid-April.
In April, the rainfall recorded by the Met Office was 36 per cent in excess of what it calls the normal average.
In April this year rainfall occurred on 28 days in sharp contrast with the usual 11 rainy days.
This year, May too was wetter than normal with 30 rainy days in sharp departure from the usual 18 rainy days.
The Met Office says that the rains in the pre-monsoon months of March, April and May occur in Bangladesh from thunderstorms.
The Met Office, however, said that due to lack of research it was unable to come to conclusion that change in rainfall patterns took place under the impact of climate change.
But the Met Office found unmistakable evidence of sharply increased intensity of thunderstorms in Bangladesh.
Weatherman SM Quamrul Hassan said that thunderstorms occur in pre-monsoon months when dry and hot air enters Bangladesh from the northwest and meets cold and moist air coming from the Bay of Bengal and the consequent energy supply feeds the system of thunderstorm formation.
Normally the air flows break for which thunderstorms cannot form continuously, he said.
But this year as there was no respite in the air flows from the sea and the northwest thunderstorms occurred almost every day in two out of the three pre-monsoon months.
‘This was an unusual weather phenomenon in Bangladesh,’ said Quamrul.
A 2009 research conducted by University of Malaya in Malaysia for which rainfall data was analyzed for 48 years since 1958, found that rainfall in pre monsoon months increased by 2.47 mm every year over the period studied in Bangladesh.
The research predicted that rise in sea surface temperature may result in the flow of stronger and more continuous winds from the Bay of Bengal during pre-monsoon months to cause more rains.
This year Bangladesh weather forecasters reported to have had a rare sight of unusual number of towering columns of thunderclouds hanging over the sky in pre-monsoon months.
People did not have the opportunity to have a glimpse of it from above, but they felt it on the ground in their own way.
Many pre-monsoon morning skies wore the look of night after heavy clouds enveloped them. Motorists had to keep headlights on while driving even after the sunrise as it was eclipsed by dark clouds.
Lightning struck with a frightening frequency and killed almost 200 people between March and mid-May.
‘It’s the worst year of thunderstorms,’ said Rashed Zaman, a 40-year-old Dhakaiya.
In 2017, a NASA funded climate research studied rainfall data of 34 years since 1966 recorded by 152 stations in Europe and Asia and came to the conclusion that global warming was causing more thunderstorms in European and Asian countries than before.
According to the study rains after thunderstorms increased by 18.4 per cent due to the global warming increase per degree Celsius.
‘As a consequence, the transitional seasons of spring and fall are becoming more summerlike in terms of precipitation characteristics, extremes, and intensity,’ found the study.
Thunderstorms are occurring in increasing intensity at many places across USA, Europe and Asia.
Japanese meteorologists said a ‘train of thunderstorms’ caused the recent devastating floods in their country.
Bad news is that the researchers noticed a rise in thunderstorm triggering energy in air in Bangladesh.
BUET physics professor Rafi Uddin, after analyzing 15 years data from 1998, found that the energy, academically called ‘Convective Available Potential Energy’ rose above 2,000 joule/kg in 2013 from around 1,000 joule/kg in 1998.
‘We don’t have enough data to come to a conclusion. Still, we can say that tis energy has been rising,’ said Rafi.
In April, spells of flood submerged 78,000 hectares of standing crops in 28 districts of Bangladesh.
Floods and in March and April last year, caused by unusually heavy rains reduced rice production by a million tonnes besides creating a severe fodder crisis in the country.
Amid the weather appearing to behave in a crazy manner people were amazed to hear cuckoos singing after the spring was over.
Wildlife expert Anisuzzaman Khan said frugivore cuckoo comes close to humans in spring, when flowers bloom.
‘But, lately, cuckoos stayed n the gardens long after spring was over,’ said Anisuzzaman.
‘Animals like cuckoos are indicator species. Perhaps they are sending the message: a change is taking place,’ Anisuzzaman said.
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