On a day when the monsoon made its official arrival on Indian mainland, the Indian Meteorological Department (IMD) had more good news to share. It has upscaled its forecast for the south-west monsoon this year, to a 102 per cent of the long-period average (LPA). In its first monsoon forecast on April 15, the IMD had said the monsoon will be 100 per cent of the LPA.
Rainfall between 96 to 104 per cent of the LPA are considered "normal" monsoon. Statistically, too, the IMD has improved the chances for an "above normal" monsoon to 25 per cent from the earlier forecast of 21 per cent. The chances for a below normal monsoon, therefore, have dipped to 15 per cent from the previous forecast of 20 per cent.
However, not all the news is good. The northeast region, which has been seeing declining monsoon precipitation for the last few years, will continue to receive less rains, only 96 per cent of the LPA this year. Though this prediction is still within the normal range, it is much lower than the 102 per cent predicted for the entire country. Regionally, north-west India is expected to receive 107 per cent of the LPA, which is in the above normal range, and may not necessarily be a good thing, either. Central India is expected to get 103 per cent of the LPA, while the south peninsula is expected to receive 102 per cent of the LPA.
The monthly rainfall over the whole country is likely to be 103 per cent of the LPA in July and 97 per cent of the LPA in August, with a model error of nine points in this prediction. July and August are the main rain giving months, when the entire country is covered by the monsoon.
While a number of factors contribute to the monsoon performance, there are some factors decidedly in favour this year. Towards the latter part of the season, the El Nino Southern Oscillation will be colder than usual, and a weak La Nina should develop. El Nino usually leads to a poor monsoon, while La Nina brings more rain. Also, the Indian Ocean Dipole will continue to remain neutral.
Earlier in the day, the government announced that the southwest monsoon had arrived in Kerala. June 1 is the date of arrival, and the monsoon kept its date this year. The IMD had, earlier, worried that the rains might arrive a few days behind the schedule, by June 5, though the first forecast had kept June 1 as the date of arrival.
Meanwhile, private forecaster Skymet announced the monsoon's arrival on May 30. While Earth Sciences secretary M. Rajeevan Nair did not take names, he stressed on Monday that the arrival of the monsoon is decided upon by a "range of subjective conditions, and not arbitrary ones." These conditions include the wind speed and direction (south to south west), the depth and spread of the cumulus cloud cover, and the amount of rainfall received in the 14 stations in Kerala and nearby areas, designated for the purpose of announcing the first monsoon rains.
Over the last two days, Kerala has received widespread rains, and by Monday, 80 per cent of the stations have recorded over 2.5mm of rainfall, thus fulfilling the criteria for announcing the arrival of Monsoon 2020.
There is also a depression in the Arabian Sea that is building up into a cyclone off the north Maharashtra-south Gujarat coasts. "It is very likely to move nearly northwards till June 2 morning, and then recurve north-north-eastwards and cross north Maharashtra and south Gujarat coasts between Raigad and Daman by June 3. This system, which could be christened Cyclone Nisarga, if it develops into a cyclone, will bring heavy precipitation to the region. However, this should not be considered as part of the monsoon rain for the area," Nair said.
The system, however, might suck out the moisture from the region and delay the advance of monsoon northwards, leading to what meteorologists call a hiatus in the monsoon.
While monsoon forecasting has got very refined over the last decade, with the implementation of the National Monsoon Mission and the deployment of a series of weather satellites, the nature of the monsoon itself has changed, too. The needs of forecasting, too, have evolved. Now, the forecast of a normal monsoon for the entire season does not mean much, since the rainfall is not evenly distributed and there are several more days of extreme weather, with large lulls in between.
Nair said the IMD was researching on predicting in advance how many heavy rain days are expected, and also about when there should be active spells and breaks in the monsoon. However, it will be some years from now that these services will be available to the country.
Specific forecasts help city planners and farmers get ready in advance. For instance, if the urban planners have advance warnings over when the heavy wet spells are likely, they can initiate mitigation measures like closing schools or evacuating people from flood-prone areas and clearing out the drainage. Similarly, farmers can rationalise when to irrigate the fields.
Last year was a classic example of extreme weather. While at the end of the season, the monsoon score was at a little above normal, its time and spatial distribution caused both drought and flood.
June, the first monsoon month, was so dry that the country went into a 33 per cent rain deficit by the end of the month. Later, with heavy wet spells, there were floods in Surat, Pune, Bihar and Kerala. The monsoon also retreated a month behind the schedule.
