Wicked surprise: On the northeast monsoon

As India recovers from a monsoon-deficit year, there is both hope and trepidation regarding the prospects for that ‘other monsoon’, or the ‘northeast monsoon’. While contributing only around a quarter of India’s annual rainfall, it is largely focused on the south-east peninsula regions of Tamil Nadu, Puducherry, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and Keralam. The southwest monsoon, influenced by a strengthening El Niño, has already left its desiccating mark. Rainfall from June-September was 759.4 mm against 868.6 mm, a 12.6% deficit, the driest in 11 years. This has impacted kharif sowing and is reflected in food inflation.

The India Meteorological Department (IMD) has said that this year, the northeast monsoon rainfall, spanning October to December, would likely be ‘normal’, meaning in line with a 50-year average and within a 12% error window. Most parts of the country, it said, are expected to receive below-normal rainfall, except some areas of northwest India and southern parts of peninsular India, where rainfall is likely to be normal to above-normal. The wide error window, however, is far less precise than its forecasts for the southwest monsoon with its margin of 5%, and can sometimes make the northeast monsoon the bearer of nasty surprises. For instance, December 1, 2015, saw the city of Chennai deluged by its heaviest rainfall in 24-hours in over a century; at least 500 lives were lost and 18 lakh people displaced in the State. That year and the present are linked by a common thread: a powerful El Niño. Associated with the heating up of the Central Pacific, the El Niño is linked to the drying up of the southwest monsoon rains but also yoked — not always — with a vigorous northeast monsoon. Other than in 2015, several El Niño years, such as 1997 and 2009, have been associated with above-normal rainfall between October and December in Tamil Nadu though El Niño years, such as 2002 and 1982, saw a poor northeast monsoon (and a predictably bad southwest monsoon). While the climate mechanisms linking a vigorous northeast monsoon and El Niño are still to be fully understood, it appears the warming patterns of the El Niño tend to deflect rain-bearing cyclonic circulations in unpredictable ways. Therefore, the Centre and the southern States ought to take enough precautions: from clearing up stormwater drains, fortifying shelters, making provisions for infrastructure damage and tightening weather warning forecasts to prepare for torrents.