Maarg Manthan · Topic 8.7

Impact of El Niño and La Niña on the Indian Monsoon

Geography › Physical Geography of India · Topic 8.7

El Niño and La Niña change the Indian monsoon by shifting the Walker circulation over the Pacific, which alters where air rises and sinks over the Indian region. In most El Niño years the southwest monsoon is weak and erratic, with deficits in central and north-west India, delayed sowing and higher risk of drought, though the link is not exact. La Niña years usually bring a strong monsoon and, sometimes, floods. Because about half of India's farmland depends on rain and the monsoon supplies roughly three-fourths of the annual rainfall, ENSO is a main concern for farm output, prices and policy.

6 min read · UPSC Prelims · Geography · Physical Geography of India

At a Glance

El Niño Weak, erratic monsoon; drought risk
La Niña Strong monsoon; flood risk
Monsoon share About three-fourths of annual rain
Rainfed farmland About half of the net sown area
Forecasting IMD, Monsoon Mission
Exam link UPSC Prelims, Geography: Physical Geography of India

Where Does It Fit?

This topic applies the global cycle of El Niño and La Niña to India, after the monsoon mechanism. It looks at what these swings do to India’s rainfall, farming and economy, while the climatology of the cycle itself is in the macro on the atmosphere. Previous topic: Monsoon Mechanism: Traditional and Contemporary Theories (Air Mass Theory, Jet Stream Theory). Next topic: Seasonal Cycle of Indian Climate: Cold Weather, Hot Weather, Southwest Monsoon, Retreating Monsoon Seasons.

How Do El Niño and La Niña Reach India?

In short: the warm or cool water in the Pacific changes the air circulation across the tropics, and the monsoon is part of that circulation.

El Niño: warm water spreads over the central and eastern Pacific, and the area of rising air moves east from Indonesia. This weakens the Walker circulation and the monsoon cross-equatorial flow, so air sinks over parts of India and rainfall fails.
La Niña: cool water in the eastern Pacific strengthens the Walker circulation and the warm pool near Indonesia, which pushes more moisture to India.
Timing: an El Niño that develops early, before or during June, hurts the monsoon more than one that begins late in the season.
Indian Ocean Dipole: a positive phase can offset El Niño, as it did in 1997, while a negative phase can add to its effect. The global pattern is explained in El Niño and La Niña: ENSO and the Indian Ocean Dipole Effect and Influence of El Niño/La Niña on the Indian Monsoon.

What Are the Effects on Rainfall and Farming?

Aspect	El Niño year	La Niña year
All-India rainfall	Often below normal; the 2002 and 2009 droughts and the poor monsoons of 2014 and 2015 are examples	Often normal to above normal
Spread of rain	Long dry spells and breaks; worse in central, north-west and peninsular India	More even, but heavy spells can flood Assam, Bihar, Keralam (Kerala) and other regions
Kharif sowing	Delayed; lower area under rice, pulses, oilseeds and cotton	Good sowing and reservoir storage
Rabi crop	Reduced soil moisture and reservoir water	Better water for irrigation
Food prices	Higher prices of pulses, vegetables and cereals	Easier supply and prices
Temperature	Heat waves are more likely; the year after is often record warm	Cooler in general

The effect on the economy goes beyond farming. Farm income drives rural demand for goods, hydropower falls when reservoirs are low, and food inflation can force changes in trade policy, such as limits on exports of rice and sugar in an El Niño year. Drought also raises the demand for rural employment under MGNREGS.

How Is Monsoon Drought Defined and Managed?

Normal rainfall: the long-period average of the monsoon over 1971 to 2020 is about 87 cm. A season between 96 and 104 per cent of this average is called normal, and below 90 per cent is deficient.
Meteorological drought: declared by the India Meteorological Department when the seasonal rainfall deficiency is more than 10 per cent of normal over the country, and by more than 20 per cent of the area experiencing it.
Agricultural drought: declared by states, based on soil moisture, crop condition and rainfall, under the Drought Management Manual.
Response: contingency crop plans, seed supply, relief such as fodder and drinking water, buffer food stocks of the Food Corporation of India, crop insurance under the Pradhan Mantri Fasal Bima Yojana, and employment under MGNREGS.
Efficient water use: micro-irrigation, short-duration varieties and rainwater harvesting reduce the risk, as in Water Resources: Utilization, Water Contamination, Conservation Methods.

How Is the Impact Forecast?

The India Meteorological Department issues its long-range forecast of the monsoon in April and updates it in late May or June, using statistical and dynamical models. The condition of ENSO and the Indian Ocean Dipole, the snow cover of Eurasia, and temperatures of the seas around are inputs. The Ministry of Earth Sciences launched the National Monsoon Mission in 2012 to build coupled ocean-atmosphere models, which now give forecasts from days to a season ahead, and in 2024 the Cabinet approved Mission Mausam to improve weather and climate services further. As an analytical point, the ENSO link is the best-known predictor of the monsoon, but it explains only part of the variation, and in recent decades its strength seems to have changed, so forecasts have to look at several factors together, as in Monsoon Mechanism: Traditional and Contemporary Theories (Air Mass Theory, Jet Stream Theory).

Why Is This Topic Important?

Agriculture Monsoon drives farm output
Policy Drought definition and response
Forecasting IMD and Monsoon Mission

What Came Next?

The next topic describes the seasonal cycle of Indian climate: the four seasons of the year. Next topic: Seasonal Cycle of Indian Climate: Cold Weather, Hot Weather, Southwest Monsoon, Retreating Monsoon Seasons.

Key People and Terms

Long-period average Average seasonal monsoon rainfall
Meteorological drought Rainfall deficit above 10 per cent
Walker circulation East-west circulation over the Pacific
Monsoon Mission MoES programme for monsoon models
Contingency plan Alternate crop plan for poor rain
Kharif Crops sown with the monsoon

Exam Corner

Points to Remember

El Niño usually means a weak monsoon.
Meteorological drought: deficit above 10 per cent.
The monsoon gives about three-fourths of annual rain.
National Monsoon Mission began in 2012.
A positive IOD can offset El Niño.

Do Not Confuse With

Meteorological and agricultural drought Rainfall deficit versus crop and soil stress
El Niño and monsoon break Pacific warming versus a pause in the monsoon rain
LPA and normal rainfall The average versus the range around it

Memory Hook

Pacific warm, monsoon harm; Pacific cool, the rains rule.

Mains Angle

Questions ask for the impact of the monsoon on the economy and for drought management. These points add depth.

Rainfall Link with ENSO and IOD
Economy Farm output, prices, power
Response Forecasts, insurance, relief

A Question You May Face

An original practice question, not a past paper question.

“Examine the impact of El Niño and La Niña on the Indian monsoon and discuss the measures to reduce their effects on agriculture.”

How to Answer

Mechanism Walker circulation shift.
Effects Rain, crops, prices.
Limits IOD and timing.
Measures Forecast, insurance, irrigation.

GS Relevance

Prelims: effect of ENSO on the monsoon, drought definition, forecasting. GS Paper 1: climate of India; GS Paper 3: agriculture and disaster management.

Frequently Asked Questions

How does El Niño affect the Indian monsoon?

El Niño warms the central and eastern Pacific and shifts the area of rising air eastward, weakening the Walker circulation and the monsoon flow. In most El Niño years Indian rainfall is below normal, with long dry spells and a higher chance of drought, although other factors like the Indian Ocean Dipole can offset the effect.

How does La Niña affect the Indian monsoon?

La Niña cools the eastern Pacific and strengthens the Walker circulation, which usually brings a good monsoon, with normal to above-normal rainfall in many years. The heavy rain of some La Niña years can also cause floods in parts of India, such as Assam, Bihar and the Western Ghats.

What is a meteorological drought in India?

The India Meteorological Department declares a meteorological drought for the country in a monsoon season when the all-India rainfall deficit exceeds 10 per cent of the long-period average and more than 20 per cent of the area experiences drought. A rainfall below 90 per cent of the average is called deficient.

Why is the monsoon important for the Indian economy?

The monsoon brings about three-fourths of India's yearly rainfall and about half of the net sown area depends on it. It affects crop output, farm incomes, food prices, reservoir levels and hydropower, and rural demand, so a failed monsoon slows the economy and raises food inflation.

Which agency forecasts the monsoon in India?

The India Meteorological Department forecasts the monsoon, issuing its long-range forecast in April and an update in May or June. The Ministry of Earth Sciences supports it through the National Monsoon Mission begun in 2012 and, from 2024, Mission Mausam, which build better models using ENSO and ocean data.

PYQ Practice — Statement Analysis

1 El Niño years are generally associated with deficient monsoon rainfall in India.

True

But the relation is not perfect.

2 A monsoon drought is declared when the deficit is above 50 per cent.

False

It is above 10 per cent of normal.

3 About half of India's net sown area depends on rainfall.