How the South-West Monsoon left weather forecasters IMD, Skymet high and dry
Vinson Kurian Thiruvananthapuram | Updated on October 15, 2019 Published on October 15, 2019
Researchers and scientists not only here but even abroad have had a tough time predicting the whimsical course of the monsoon year after year.
North-East monsoon expected in two days: IMD
While the IMD had predicted rainfall would be 96% of the Long Period Average in its early forecast, Skymet put this at 93%. Both predictions went awry with actual rainfall at 110% of the LPA
Myriad factors, many still beyond our comprehension, seem to combine decisively to preside over the fate of the annual Indian monsoon, among the most complex weather systems on the face of the planet. Be it the Indian Ocean in our backyard, the grander Pacific to the Far-East, the snow-bound Arctic to the Far North or the inhospitable Tibetan landscape to the North-East — they all leave a stamp on the monsoon's performance during a given year.
They are 'known unknowns' at best or 'unknown knowns' at worst, depending on how scientists/researchers prefer to approach this spectacular weather event. And every year, they have an impact on the monsoon, as they did in no small measure this year.
It was supposed to be a below-average monsoon. In its early forecast, the IMD had predicted rainfall would be 96 per cent of the long period average (see table). Private weather forecaster Skymet put the figure at 93 per cent. Both predictions, however, went awry with actual rainfall coming in at 110 per cent of the Long Period Average. Even the best global weather models were unable to foresee this outcome. And therein lies a tale.
'The real finance minister'
Two-thirds of the country lacks irrigation, which leaves its farm economy at the mercy of the monsoon, prompting former finance minister and former president Pranab Mukherjee to cite it as the country's 'real finance minister.'
And not without reason. The economic well-being of more than 600 million people is intrinsically tied to the whims and fancies of this weather system, which delivers 70 per cent of the annual rainfall.
Sowing of major kharif crops is timed with the likely onset of annual rains for a given season and any uncertainty with respect to its arrival and progress can put paid to farmers' dreams.
This, in turn, can spell havoc with rural farmers' incomes and their capacity to spend, apart from causing food inflation to spiral beyond control, with direct consequences on interest rates.
There is a range of industrial sectors that instantly recoils at the monsoon-led misfortunes of the teeming rural population — among them FMCG, automobiles, tractors and fertilisers.
Not just this. The rains also have an impact on power generation in major Indian states. Below-average monsoon rainfall has often been associated with an increase in the number of blackouts.
Not drought-proof
This is especially so in States such as Punjab and Kerala, where poor monsoons have bequeathed harsh summers and an increase in the number and length of power outages.
The heightened demand invariably translates into higher unit costs, playing with productivity and operations for user industries across the spectrum.
Meanwhile, an above-average monsoon and associated rains, such as in the monsoon just concluded, can mean cascading implications for industries such as construction and transport. Cement and other construction materials often face increasing demand leading to a price spiral during such a phase, raising costs. The rains also interfere with time schedules of major ongoing projects.
So when and where the monsoon will arrive and how it will deliver rain is of paramount importance to not just farmers but also some crucial stakeholders of the larger economy. Suffice to say long-range monsoon forecasts are awaited with bated breath.
'Predictably unpredictable'
Researchers and scientists not only here but even abroad have had a tough time predicting the whimsical course of the monsoon year after year. The just-concluded 2019 monsoon has been no exception with the first month of June ending up with a 33 per cent deficit.
But the subsequent three months saw their best precipitation (or worst, depending on which side of the Vindhyas you are!), leaving the landscape swamped by the fury of the rain.
This was way beyond anything either the India Meteorological Department (IMD), India's equally revered and reviled national forecaster, or domestic private forecaster Skymet Weather or even leading global weather models had bargained for.
Still, in the words of Mrutyunjay Mohapatra, Director-General, the IMD managed to save itself some blushes by predicting normal rainfall (96-104 per cent of the long-period average, LPA) for the season.
This was when several global models had indicated a strong possibility of continuation of a 'monsoon-killer' El Nino episode in the Equatorial Pacific and possibly below-normal rains for India.
IMD'S monsoon tryst
The IMD's quantitative forecast for the season's rainfall issued in April and May was 96 per cent of the LPA, with a model error of ± 5 per cent and ± 4 per cent of the LPA, respectively.
While issuing the forecasts based on the IMD's models, it was suggested that the El Nino episode would further weaken and a positive Indian Ocean Dipole (IOD) event would emerge in the Indian Ocean.
An El Nino, marked by warming of the East Equatorial Pacific, has been known to dry up the monsoon and trigger droughts, though with honourable exceptions, such as in 1997.
In contrast, a similar anomaly in the Indian Ocean in which its western basin warms up relative to the East (a positive IOD), boosts an ongoing monsoon, as was spectacularly evident this year.
Moreover, the IMD had also predicted that the monsoon's performance would be better in the second half (August and September) compared to the first half (June and July).
Standout features
The IMD's analysis on the weakening of El Nino and development of a positive IOD and the second half monsoon rainfall being above normal proved to be right in the end. The terrific run of the 2019 monsoon also left behind a list of stand-out statistics.
They are as follows:
After 1994 (110 per cent of LPA), rainfall received in 2019 (110 per cent of LPA) is the highest season rainfall received by the country as a whole.
During 18 of the last 19 years (2001-2019), North-East India has received seasonal rainfall less than the regionally applicable LPA, with the exception of 2007 (110 per cent of LPA).
This indicates that the seasonal rainfall over North-East India is passing through a below-normal epoch. After 1931, this is the first time that the seasonal rainfall is more than the LPA even after the June rainfall deficiency was more than 30 per cent of LPA.
After 1996 (119 per cent of LPA), this is the highest recorded August rainfall (115 per cent of LPA). This is also the second highest September rainfall (152 per cent of LPA) after 1917 (165 per cent).
After 2010, this is the first time rainfall during the last three months (July to September) was above the LPA. After 1983 (142 per cent above LPA), 2019 recorded the highest cumulative rainfall during the August-September period (130 per cent).
Monsoon long-range forecast Vs actual rainfall (% of LPA)
* LPA - long period average LPA is the average rainfall for June-September from 1951 to 2000 calculated at 89 cm
*Source: IMD, Skymet Weather
The IMD admitted that quantitatively, the realised rainfall during the second half was more than it had predicted. But its forecast for onset over Kerala proved to be correct.
The IMD also got it right with prediction of the date of commencement of withdrawal of the monsoon from North-West India around October 10 as against the normal date of September 1.
The actual date of withdrawal turned out to be only a day earlier (October 9), the most delayed since October 1 in 1961, followed by September 30 in 2007.
Skymet's experience
Jatin Singh, Managing Director of Skymet Weather, the other major agency that makes long-range forecasts, points to the roller-coaster ride of the monsoon this year.
This was an El Nino year, but the El Nino started collapsing after June, even as the monsoon-booster positive IOD phase kept growing stronger, Singh told BusinessLine.
According to Jatin Singh, this had resonated with helpful MJO signals that periodically passed the Indian Ocean, all of which powered the monsoon to a new peak, delivering a surplus of 10 per cent.
Read also: Monsoon logs a double-digit surplus as season concludes
MJO refers to the Madden-Julian Oscillation wave, a low-pressure wave packing clouds, moisture and rain, that traverses periodically from the East to the West over the Indian Ocean with a significant bearing on rainfall under its footprint.
Skymet Weather, Singh said, had started giving monsoon forecasts in 2012 under the guidance of the legendary R Sikka, also known as the 'monsoon man' of India.
"Despite being a long-term forecast based on models and numerical data, we are proud to say that the accuracy level of Skymet with respect to the South-West monsoon is 70 per cent,"he said.