We Indians keep a close eye on monsoon progress each year, which is very vital for the Indian economy and agriculture perspective.
The arrival of seasonal rainfall after harsh summers is welcome with great pomp. As per the national forecasting agency, the rainy season stretches from 1 June to 30 September chronologically. The arrival of monsoon over the Indian mainland starting from Kerala is announced by Indian Meteorological Department, precisely IMD, keeping in mind the set criteria based on various parameters including rainfall, winds and Outgoing Longwave Radiations (OLR).
This year, the monsoon arrival was announced by the national agency on 29 May as against the earlier predicted date of 27 May, yet 3 days in advance. But the controversy arose when the country's largest private weather forecaster Skymet India objected to the arrival in view of ignorance of set criteria overlooked by IMD. Many budding weather enthusiasts and bloggers also supported Skymet as the widespread rain eludes Kerala.
The set criteria for announcement of monsoon arrival:
- If after 10th May, 60 per cent of the available 14 stations, viz Minicoy, Amini Divi, Trivandrum, Punalur, Kollam, Alappuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu, and Mangalore report rainfall of 2.5mm or more for 2 consecutive days, the onset over Kerala be declared on the 2nd day, provided the winds and OLR criteria also remains in concurrence.
- Wind Field: Depth of westerly winds should be maintained up to 600 hPa, in the box 0°-10°N and 55°-85°E. The zonal wind speed over the area bounded by 5°-10°N and 70°-80°E should be of the order of 15-20 knots at 925 hPa.
- OLR: INSAT derived OLR value should be below 200 Watt/ sq. meter in the box confined by 5°-10°N and 70°-75°E.
Skymet argues IMD overlooked its own set of specified criteria for declaring onset of monsoon. According to Skymet, though OLR and Winds were established, the main norm of rainfall fell short on 28 May and 30 May.
"Onset conditions were fulfilled only for one day, 29thMay. Day prior (28th May) and day later (30thMay), merely </= 40% of the designated stations met the rainfall criteria. Declaring monsoon based on single day observations amounts to gross violation of standards, never attempted in the past," claims Skymet.
Monsoon is a pulse of winds travelling alongside ITCZ, a trough of low pressure, which strikes the country and essential for sowing and irrigation of crops along with its direct influence on Economy, monsoon still holds the utmost importance.
Meanwhile, IMD in the press release on Tuesday, revised the long-range forecast of monsoon to 103 per cent from the earlier predicted 99 per cent with an error margin of ±4 per cent. IMD also reiterated the onset of monsoon and tried to clear the air over the erupted controversy with the press release stating it to be a weak onset.
As per the data retrieved from IMD, Minicoy received 1.3 mm, 16 mm and 12 mm of rainfall on 28, 29 and 30 May respectively. No rainfall was observed in Thiruvananthapuram, Kollam, Kudlu and Kannur on 28 May. Similarly, Amini Devi, Punalur, Alappuzha, Kottayam, Kochi, Thrissur ,Kozhikode, Thalaserry and Mangalore received 0.4 mm, 3.6 mm, 9.4 mm, 0.2 mm, 8.0 mm, 17.2 mm, 0.7 mm. 7.2 mm and 7 mm of rainfall respectively on 28th May. Meanwhile on the date of onset I.e, 29th May, Recorded rain at 14 Monsoon stations is as follows:
Minicoy 16 mm
Amini Devi 0.5 mm
Thiruvananthapuram 22.7 mm
Punalur 13.4 mm
Kollam 6 mm
Alappuzha 8.4 mm
Kottayam 9.4 mm
Kochi 5 mm
Thrissur 2.5 mm
Kozhikode 8.6 mm
Thalaserry 2 mm
Kudlu 18.4 mm
Mangalore 20 mm
Surprisingly, on 30 May, Thrissur, Kozhikode, Thalaserry, Kannur, Kudulu, Mangalore and Amini Devi recorded nil rainfall.
Notably, last week Kerala has had a massive week in terms of rain but currently rain is scattered in the state and the common man doesn't care about whether the set pattern is followed, all they want is the arrival of rain showers to trench their thirst but declaring monsoon without meeting the criteria impacts historical data records as well as scientific research which will be based on monsoon onset data of the meteorological department.