La Nina, El Nino set off opposing rainfall patterns in NE in last two years

After the onset of monsoon this year in the second week of June, the two northeastern states of Assam and Meghalaya have been receiving high volumes of rainfall.

According to weather department data, in June Assam has received 389.7 mm rainfall which is 26% excess to normal. Meghalaya also witnessed excess rain, 30% above the normal range.

However, Manipur and Mizoram were described as rain deficit by the Met department officials. The other four states in this region -- Tripura, Arunachal Pradesh, Nagaland and Sikkim -- witnessed normal rainfall.

The excess rain in Assam has caused a chaotic situation in the state where at least 19 districts are inundated by flood water. The major rivers like the Brahmaputra, Manas, Puthimari and Pagladiya are flowing above the danger level.

However, a state government official said that the flood situation cannot be solely linked to the rain in Assam.

"Although Assam has witnessed slightly excess rainfall this month, the heavy rain in parts of Bhutan recently has been the primary cause of the flood," he added.

Sanjay O'Neil Shaw, the director of the regional meteorological centre at Guwahati said, "The monsoon has arrived in the northeast on June 10. The ongoing rainfall is due to the monsoon and was expected. We are anticipating more rain in the coming days."

Meghalaya has also received excess rainfall in June which led to recurrent disruption in road connectivity. The highway connecting Southern Assam, Tripura, Mizoram and Manipur which goes through Meghalaya witnessed repeated landslides this month resulting in disruption of vehicular movement.

"The monsoon in the northeast almost has a usual pattern over the years. Sometimes it rains heavily in some parts of the region while the other areas receive less rainfall. The situation also changes very quickly as often the monsoon wind changes its direction," Shaw mentioned.

Last year, the northeast received heavy pre-monsoon showers which wreaked havoc in Dima Hasao district in Assam. Floods also occurred in Assam in May that time.

However, this year, the entire northeast was rain-deficit and 38% below normal rainfall occurred in the previous month. Heat waves swept Assam and Meghalaya which forced the state administrations to revise the school timings to make it easier for the children to study.

Speaking to IANS, Bhupendra Nath Goswami, former director of the Indian Institute of Tropical Meteorology said, "The rising mercury level is somewhat linked to global warming and all. But, the rain patterns in the last two years were consistent according to La Nina and El Nino effects."

According to Goswami, when La Nina happens, Assam and the northeast receives more rainfall in May just before the beginning of monsoon. After the onset of monsoon, the northeast receives less showers compared to other parts of the country.

"In 2022, La Nina was happening and rains were lashing parts of NE in the month of May. But during July to September, more rain happened in other parts of the country in comparison to here. This was exactly in accordance with the La Nina effect," he said.

Goswami added that as El Nino is sweeping the country this time, the exactly opposite pattern of rainfall is likely to happen.

"This year, the northeast got little rain in May and I expect that more rainfall will occur between July and September," he added.

As per the veteran climatologist, due to La Nina and El Nino effects, opposing rainfall patterns are noticed in these two years, however, there is no unusuality seen in the overall climate.