Why did IMD declare monsoon early?
Experts did not take too kindly to IMD’s decision, which, strangely, came only two days after the body suggested the onset of the monsoon over Kerala would be delayed — this, a few weeks after claiming the onset would be early
Has the monsoon arrived? Or not?
Well, the India Meteorological Department or IMD says it has. But IMD’s own criteria for declaring the onset of the monsoon says it has not.
The monsoon is declared when eight stations across Kerala, Lakshadweep, and Karnataka, receive a minimum of 2.5 mm of rain for two consecutive days. On the day IMD chose to announce the onset of the monsoon, Sunday, only five did.
It wasn’t immediately clear why IMD jumped the gun -- it never has in the past -- but its head insisted its call was right.
“Even if we don’t meet the rainfall criteria for the second day, it doesn’t make a huge difference. The criterion was met on Saturday which is why onset was declared. We cannot expect that the criteria will be met every day. Tomorrow again rainfall will increase,” said M Mohapatra, director general, IMD responding to criticism by independent meteorologists on declaring monsoon onset prematurely.
Experts did not take too kindly to IMD’s decision, which, stranegly, came only two days after the body suggested the onset of the monsoon over Kerala would be delayed -- this, a few weeks after claiming the onset would be early. Yes -- there was a flip, then a flop, then a flip again.
“The monsoon’s onset over Kerala is a well-defined event. The onset criteria are based on the findings of multiple research studies spanning over five decades, which nicely link large-scale atmospheric conditions of the monsoon to rainfall occurring over Kerala. Thus, there should not be any room for subjectivity or assumptions in the onset declaration,” said Akshay Deoras, an independent meteorologist and doctoral researcher at the UK’s University of Reading.
“The monsoon onset criteria have badly failed. The monsoon surge in rainfall is not there. We do not hope to see widespread heavy rain over Karnataka, Kerala, Tamil Nadu during the next few days and the chances of monsoon progressing are also minimal during the next 4-5 days. Since IMD has declared monsoon onset so we are calling it monsoon but this the pre-monsoon pattern of showers. In fact, monsoon could have been declared earlier around May 23 or 24 when there was heavy and widespread rainfall over peninsular India,” said Mahesh Palawat, vice president, climate change and meteorology, Skymet Weather.
Here’s what the norm has been: If, after May 10, at least 60% of 14 stations — Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore — report rainfall of 2.5 mm or more for two consecutive days, the onset of the monsoon over Kerala will be declared on the second day, provided the wind pattern is south-westerly and Outgoing Longwave Radiation (OLR) is low. OLR represents the total radiation going to space emitted by the atmosphere or extent of cloudiness.
IMD in a statement on Sunday said the depth and strength of westerly winds had increased; that cloudiness over southeast Arabian Sea and adjoining areas of Kerala had improved meeting the outgoing long wave radiation (OLR) criterion; and that there has been widespread rainfall activity over Kerala during the previous 24 hours and that out of 14 rainfall monitoring stations evaluated for declaring onset of monsoon over Kerala, 10 stations received rainfall of 2.5 mm or more.
On Sunday, this criteria was not met.
Rainfall was reported at few places in Kottayam, Kollam, Alappuzha, Wayanad and Ernakulam districts on Monday, according to IMD’s Thiruvananthapuram office, but total was yet to be tabulated.
Declaring early monsoon onset could lead to confusing messaging to farmers, Skymet’s Palawat added. “For example, from the current projections we can say that south Maharashtra, Madhya Maharashtra, Telangana, Andhra Pradesh, Karnataka, Kerala and Tamil Nadu will receive good rains around June 10. So farmers there should wait for rains for sowing or they have to re-sow which has a huge cost. There is political pressure to declare monsoon onset but these aspects are important.”
“Declaring a weak onset of the monsoon could be a challenging task since the rainfall criterion often remains on the borderline. However, the onset criteria must not be overlooked since it could affect research and planning of agricultural activities in India,” added Deoras who also analysed data from IMD’s 14 stations on Sunday and Monday.
HT reported on Sunday that IMD changed its monsoon onset forecast a couple of times. On May 14, the department predicted that monsoon was likely to make landfall over Kerala on May 27, five days ahead of its normal onset date. On Friday, it said there could be a delay of 2-3 days due to a weakening of south-westerly winds. Its extended range forecast also indicated weak rainfall over most of the country, except northeast India, from June 2 to 8.
Then on Sunday, it announced the onset. “Today IMD declared the monsoon onset over Kerala. All the conditions are met for the monsoon onset. However, the monsoon flow has weakened and further monsoon progress could be slow. At least for next one week, monsoon could be weak and not much rainfall can be expected,” M Rajeevan, former secretary, ministry of earth sciences, said on Sunday.