Generally the temperature starts rising in March in the country. Nor’wester hits by the end of the month. With the beginning of the Bengali Chaitra month, the mercury starts to increase. But this year rainfall has started already, before Nor‘westers hit.
In the past few days, dark clouds entered the territory of Bangladesh through the Bay of Bengal in the similar pattern of monsoon. There have been moderate to heavy rains from coastal areas the to north. However, the Meteorological Department says that the rains may ease over the entire country except in Sylhet next week. Temperatures may rise then and hot weather may return.
Meteorologists are concerned because of the rains similar to monsoon rains have occurred at the start of Chaitra. The Meteorological Department estimates an average of 52.2 millimetres of rain across the country in March. In its forecast for this month, the agency predicted less than normal rainfall which already has been proven wrong.
According to the meteorological department, Feni district alone has received 181 mm of rain in the last four days. And the amount of rainfall across the country has exceeded 300 mm. The gusty wind that usually accompanies the rain at this time was absent. Instead, the clouds darkened like monsoon and it rained in torrents. Bangladesh Meteorological Department held a special meeting on Wednesday morning to find the reason of sudden heavy rain.
Meteorologist Bazlur Rashid, of the meteorological department, told Prothom Alo, usually during this time there is light rain and thunder along with Nor’wester. Instead, heavy rains swept through the country like monsoon for the past couple of days. Initially it seems to be due to the east wind. But at the same time, one of the key influencers of global weather, the 'Madden-Julian Oscillation' or MJO cycle, seems to be active as well.
World Meteorological Day is being observed today, 23 March. The theme of this day this year is 'The future of weather, climate and water across generations'. The World Meteorological Organisation observes this day to raise awareness about the damage caused by weather and climate change around the world and to propagate necessary preparedness.
Three reasons for sudden rain
Meteorologists say Bangladesh witnessed reduced rainfall for past three years. The reasons for this are mainly two. First, La Niña was active over a wide area from the Pacific Ocean to the Indian Ocean. When it is active, ocean temperatures drop by 2 to 4 degrees Celsius below normal. As a result, there is less rain over a wide area from the Americas to Australia to South Asia.
On the other hand, another similar condition occurs over the region extending from the Indian Ocean to the Bay of Bengal, which is called the Indian Ocean Dipole or Indian Ocean Dipole–IOD. It was also less active for two years. It also causes lesser rains and that's what happened. This condition is responsible for less rain in the country for three years.
Meteorologists believe La Niña in the Pacific for three years and the continuation of IOD conditions in the Indian Ocean and Bay of Bengal as exceptions. Usually those two special weather conditions do not manifest for more than one to two consecutive years. Amid these conditions, another condition of global climate has become active. Meteorologists call this the 'Madden Julian Oscillation-MJO cycle'. Two meteorologists Roland Madden and Paul Julian identified this special weather condition in 1970.
The MJO also rotates in different oceans across the world. Heavy rainfall occurs in the MJO-active areas. It passed through the Arabian Sea in February and entered the Bay of Bengal in the middle of this month through the Indian Ocean. This caused the Indian Ocean and the Bay of Bengal to get warmer than normal for a week.
Meteorologists say that when La Nina and IOD become positively active, rainfall increases in the respective areas. It will happen in the Bay of Bengal causing heavier rains from April-May. After the monsoon starts in June, the rains will increase, enhancing the risk of flood.
Rashed Chowdhury, a professor at the University of Arizona in the United States and a researcher of El Nino and La Nina, told Prothom Alo, "For several years, we have seen that El Nino and La Nina are greatly affecting the weather in Bangladesh. The rainfall in Bangladesh is related to the global weather conditions. Therefore, we have to make long-term weather and rainfall forecasts in line with global weather conditions. Because, the agriculture and crop production is highly dependent on the rainfall. Therefore, our meteorological department should evaluate and provide information on the global effects of El Nino, La Nina, IOD, along with weather forecast for one or two days.”
*This report, originally published in Prothom Alo print edition, has been rewritten in English by Farjana Liakat