Context: The Northeast Monsoon (October–December) is crucial for southern India, particularly Tamil Nadu and adjoining regions, amid a deficient southwest monsoon and concerns over agricultural output and food inflation.
Northeast Monsoon: Key Features
- Rainfall contribution: Accounts for around one-quarter of India’s annual rainfall, with major impacts on Tamil Nadu, Puducherry, coastal Andhra Pradesh, Rayalaseema, south interior Karnataka and Kerala.
- Period: October to December, following the southwest monsoon season.
- IMD forecast: Northeast monsoon rainfall is expected to be normal, based on the 50-year average, with a deviation of up to ±12%.
- Regional distribution: Most parts of India are expected to receive below-normal rainfall, while parts of northwest India and southern peninsular India may receive normal to above-normal rainfall.
Southwest Monsoon Deficit and Its Impact
- Rainfall deficit: India received 759.4 mm of rainfall during June–September against the normal 868.6 mm, a 12.6% deficit, making it the driest southwest monsoon in 11 years.
- Economic consequences: Deficient rainfall affected kharif sowing and contributed to food inflation.
El Niño and Northeast Monsoon Variability
- El Niño: A climate phenomenon involving abnormal warming of the central and eastern equatorial Pacific Ocean, which can alter global atmospheric circulation and India's rainfall patterns.
- Contrasting effects: El Niño is often associated with a weaker southwest monsoon, but its impact on the northeast monsoon is variable and not always adverse.
- Historical examples: El Niño years such as 1997 and 2009 witnessed above-normal October–December rainfall in Tamil Nadu, while 2002 and 1982 experienced poor northeast monsoons.
- Underlying mechanism: Changes in Pacific Ocean warming patterns may influence the movement of rain-bearing cyclonic systems, producing unpredictable rainfall over southeastern India. The precise mechanisms linking El Niño to northeast monsoon intensity remain incompletely understood.
Chennai Floods of 2015: A Case Study
- Extreme rainfall: On December 1, 2015, Chennai experienced its heaviest 24-hour rainfall in over a century.
- Humanitarian impact: The floods caused at least 500 deaths and displaced approximately 18 lakh people across Tamil Nadu.
- Key lesson: El Niño years can bring extreme northeast monsoon rainfall, highlighting the need to prepare for both rainfall deficits and floods.
Why Is Northeast Monsoon Forecasting Challenging?
- Lower forecast precision: The IMD’s stated error window for the northeast monsoon is ±12%, compared with approximately ±5% for southwest monsoon forecasts, making precise prediction more difficult.
- Complex climate interactions: The relationship between El Niño, cyclonic circulations and regional rainfall is not consistent across years, increasing the risk of unexpected extreme rainfall.
Disaster Preparedness: Way Forward
- Urban flood management: Desilt and clear stormwater drains, restore natural drainage channels and improve urban flood-control infrastructure.
- Disaster response: Strengthen cyclone shelters, prepare emergency supplies and plan for infrastructure damage and population displacement.
- Early warning systems: Improve weather forecasting, last-mile communication and timely evacuation in flood-prone areas.
- Centre–State coordination: Ensure coordinated preparedness among the Centre, southern States, meteorological agencies and disaster-management authorities.
