Why in the News
India has just ended its driest southwest monsoon in 11 years, and the India Meteorological Department (IMD) now forecasts a ‘normal’ northeast monsoon for October to December. The forecast carries a wide error window, and a strong El Niño, the same driver present during the 2015 Chennai deluge, makes the southern States’ season hard to predict.
What is the northeast monsoon, and why does El Niño matter?
- What it is: The northeast monsoon is the ‘other monsoon’ that brings rain from October to December, after the main southwest monsoon withdraws. It works like a second, smaller rainy season for the south eastern peninsula.
- Regions it feeds: It falls mainly on Tamil Nadu, Puducherry, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and Keralam.
- Share of rainfall: It contributes only around a quarter of India’s annual rainfall, but that rain is concentrated on the south eastern peninsula.
- El Niño: El Niño is the periodic heating up of the Central Pacific Ocean. It is linked to a drier southwest monsoon over India.
- The takeaway: A season that is a small share of national rainfall can still decide floods or drought for the southern States, so its forecast carries high stakes.
What did the southwest monsoon leave behind?
- Rainfall shortfall: Rainfall from June to September was 759.4 mm against a normal of 868.6 mm.
- Deficit size: The shortfall was 12.6%, which makes this the driest southwest monsoon in 11 years.
- Cause: A strengthening El Niño weakened the southwest monsoon this year.
- Farm and price impact: The deficit has hit kharif sowing, the crops sown with the summer rains. It is also reflected in food inflation.
Why is the northeast monsoon forecast less reliable?
- IMD forecast: The IMD expects northeast monsoon rainfall to be ‘normal’, meaning in line with the 50 year average and within a 12% error window, the margin by which actual rain may differ from the forecast.
- Uneven outlook: Most parts of the country are expected to receive below normal rainfall. Some areas of northwest India and southern peninsular India are likely to get normal to above normal rain.
- Precision gap: The northeast monsoon forecast is far less precise than the southwest monsoon forecast, which carries a margin of 5%.
- Surprise risk: A wide window means a ‘normal’ forecast can still be followed by extreme rain, so the season can turn into a disaster with little warning.
How does El Niño cut both ways for the south?
- Chennai deluge: On 1 December 2015, a powerful El Niño year like the present one, Chennai received its heaviest one day rainfall in over a century.
- Human cost: At least 500 people died and 18 lakh people were displaced in Tamil Nadu.
- Wet El Niño years: Several El Niño years, such as 1997 and 2009, also brought above normal October to December rain in Tamil Nadu.
- Poor El Niño years: El Niño years such as 1982 and 2002 saw a poor northeast monsoon, along with a bad southwest monsoon.
- Unclear mechanism: The link between El Niño and a vigorous northeast monsoon is not yet fully understood. El Niño’s warming pattern tends to deflect cyclonic circulations, the swirling wind systems that carry rain, in unpredictable ways.
Challenges
- Imprecise forecasts: The wide error window gives State and city administrations little certainty when planning for the season.
- Clogged drainage: Uncleared stormwater drains turn heavy spells into urban floods.
- Weak shelters: Shelters that are not fortified cannot protect people displaced by sudden torrents.
- Back to back stress: Farmers already hit by the kharif shortfall stay exposed if the northeast monsoon also fails.
- Unsettled science: The incomplete understanding of the El Niño link limits how far forecasts can improve in the short run.
Way Forward
- Drain clearance: Southern States and their cities should clear stormwater drains before the heavy spells begin.
- Fortified shelters: State governments should fortify relief shelters in flood prone districts.
- Damage provisions: The Centre and the southern States should make advance provisions for infrastructure damage.
- Sharper warnings: The IMD should tighten weather warnings and forecasts so local authorities can act in time.
Conclusion
A ‘normal’ forecast does not mean a safe season, because El Niño has brought both floods and failures to the south. The test is whether the Centre and the southern States finish drain, shelter and warning preparations before the season’s torrents arrive.
Matching Previous Year Question
“[2017] With reference to ‘Indian Ocean Dipole (IOD)’ sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct? 1. IOD phenomenon is characterized by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean. 2. An IOD phenomenon can influence an El Nino’s impact on the monsoon. Select the correct answer using the code given below: (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 ANSWER: (b)”
