While several States reel under heatwaves, the India Meteorological Department (IMD) has forecast a bountiful monsoon for the year. In a press briefing on April 15, the agency has forecast that the rains in June-September will be 6% more than the annual average of 87 cm during these months.
Last year, El Nino – a warming of the Central Pacific and usually linked to diminished rainfall in India – dented India’s monsoon by 6%. This year, the El Nino has not yet fully faded but is expected to do so by June and progress to La Nina, a converse cooling effect that’s usually linked to surplus rainfall by the second half of the monsoon (August and September), said IMD Director-General Mrutunjay Mahapatra.
The IMD uses multiple approaches to forecast the monsoon. One is to use statistical associations and draw upon its vast historical database of over 150 years to correlate certain global meteorological parameters such as ocean temperatures and snow cover in Europe etc. to the performance of the monsoon. The other way is to use the dynamical approach, or simulating the weather across the globe on a particular day, and having powerful computers crunch the numbers to extrapolate this weather into any future day or time period desired. Both these models indicated a similar outlook for the monsoon this year, said M. Ravichandran, Secretary, the Ministry of Earth Sciences (MoES).
The IMD is expected to update its monsoon forecast in May, just ahead of the monsoon onset in June, and give more information on how the monsoon is expected to spatially distribute itself across the country. The models indicate a 30% chance of monsoon rains being over 10%, categorised as ‘excess’ in the IMD vocabulary. This is a significant jump considering that in any given year there is only a 17% chance of such ‘excess’ rain.
June and July are considered the most important monsoon months for agriculture given that a large fraction of the kharif crop is planted in these months. The agency, however, did not indicate the quantity of rainfall expected during these months.
Twin factors
One of the two factors favouring plentiful rain was a positive IOD (Indian Ocean Dipole), or a cooler than normal Indian Ocean in the east as compared to the west, which again helps bring rain to several States in southern India. Though currently ‘neutral’, it is expected to turn positive by August.
Another factor was a below-normal snow cover in the northern hemisphere and Eurasia. Historically, there was an “inverse relationship” between the levels of snow here and the monsoon, said Dr. Mohapatra.
The current forecasts also indicate that “above-normal” rain was likely over most parts of the country except northwest, east and northeast India.
