The Indian summer (June-September) monsoon impacts over 1.7 billion people of the Indian subcontinent and its timely progress, from the onset at the southern tip of India around the 1st of June till about the 27th of June, when it is generally established all over India, is crucial for India’s agriculturally dominated economy.
Besides agriculture, the summer monsoon also plays an important role in providing drinking water by recharging various rives systems & water reservoirs, especially in the peninsular and central India. Climate models have achieved only a limited success in simulating and predicting many of the complex features of Indian/Asian monsoon so far.
This year the summer monsoon was predicted to be below normal (about 93% of normal) by the India Meteorological Department by mid-April 2014. An important parameter for a below normal projection this summer was a brewing El Nino event in the equatorial Pacific Ocean. The monsoon-El Nino link has been extensively studied by many scientists in a large number of research papers and documents published in the last 30 years.
It is now generally accepted that an El Nino event (spreading of warm waters off the coast of equatorial South America) is generally associated with a weaker (summer) monsoon, while a La Nina event (opposite of El Nino, when colder sub-surface waters in response to strong easterly winds spreads in the equatorial Pacific, off the coast of South America) produces a good monsoon.
Among some of the worst monsoon droughts were 1877 and 1918, both were associated with strong El Nino events. Among some of the good (surplus) monsoon years were 1916 and 1975, which were both associated with La Nina events. Besides El Nino /La Nina, other large-scale circulation patterns like the Equatorial Indian Ocean Oscillation (EQUINO) and the enigmatic Quasi-Biennial wind Oscillation (QBO) in the Equatorial stratosphere (at about 20 km up in the atmosphere) also appear to impact Indian summer monsoon.
Let us now briefly look at the progress of this year’s monsoon so far.
The monsoon arrived at the southern tip a week late this year. After a few sporadic showers mostly in southern peninsular region, monsoon rains spread into northeast where good rains have been reported so far. Also neighboring Bangladesh (population ~ 160 Million) has received good rains so far (some flooding was reported in Bangladesh during the week-end of June 21-22 2014).
As of June 27, the monsoon rains have covered most of southern Peninsula of India (up to about 12N) and most parts of northeast India, including the city of Kolkata (second largest city with a population ~ 18 Million). However monsoon remains weak elsewhere and this is starting to cause considerable anxiety among India’s agriculture sector as well policymakers in India. Mumbai, the largest Indian city (with a population of about 25 Million) has received only about one fourth of normal rains so far and city officials are considering reduced water supply in some areas.
The Director General of India Met Dept (IMD), Mr D S Pai had a two hour emergency meeting with India’s newly elected PM Mr Narendra Modi & briefed the PM on the monsoon progress and possible impact on agriculture. The El Nino impact is being felt at this point, as convective activity over the equatorial IndiaOcean remains weak & this seems to have stalled monsoon progress.
The EQUINO appears to be in a positive phase, generating sporadic convection in the eastern equatorial Indian Ocean and if this phase of EQUINO continues, there may be revival of monsoon in the next two to three weeks. Also the QBO is in a westerly phase now, which generally favors increasing convective activity. Convective activity within the large-scale monsoonal flow provides significant amount of rains over various regions of India. Further the El Nino is only of moderate strength at this time (temperature anomaly of about 1C in the Nino 3.4 region; compare this with 1997/98 El Nino when temperature anomaly was a whopping 3C or more for several months).
Also, the phase of PDO (Pacific Decadal Oscillation, a thirty-year oscillation) being negative now, the impact of El Nino on monsoon may not be as adverse as it was in 1987 drought or a more recent drought of 2002. Per latest communiqué by the IMD, monsoon activity would resume across much of the country by about 6 July 2014. A good monsoon is essential for India’s agriculture, which today accounts for about 10% of its GDP (Gross Domestic Product) which translates to about US$ 200 billion.
Accurate simulation and prediction of Indian/Asian monsoon with a lead time of few weeks to few months still remains an intractable problem in climate science.
Madhav Khandekar is a former Research Scientist from Environment Canada and was the Expert Reviewer for the IPCC 2007 Climate Change Documents. Khandekar continues his research at present on monsoon inter-annual variability and its linkage with global weather anomalies like El Nino/La Nina.