Indian Monsoon: Mechanism, Variability & Climate Change

Why in News: The Indian monsoon is a critical climate system whose variability, changing rainfall distribution and increasing extreme events have major implications for agriculture, water security, disaster management and the economy.

~75%

of India's total rainfall comes during the Southwest Monsoon.

125 cm

Approximate average annual rainfall of India, with large spatial variation.

934.8 mm

Southwest monsoon rainfall in 2024, equal to 108% of LPA.

150 mm+

Daily rainfall threshold used in the source to discuss extreme rainfall events.

Monsoon at a Glance

Differential heating
of land & sea

→

Pressure gradient

→

Seasonal wind reversal

→

Moisture transport

→

Rainfall

Monsoon refers to a seasonal reversal of winds associated with differential heating and consequent pressure differences between land and sea.

The term comes from Arabic Mausim, meaning "season".

1. Seasonal Reversal: Southwest vs Northeast Monsoon

Southwest Monsoon — June to September

Main rainy season and provides about 75% of India's rainfall.
Normally reaches Kerala in early June and covers most of India by mid-July.
Two principal branches are the Arabian Sea branch and Bay of Bengal branch.
Western Ghats and Himalayas induce uplift and rainfall.
Crucial for crops such as rice, cotton and sugarcane.

Northeast Monsoon — October to December

Also called the retreating monsoon.
Land cools faster than the ocean, reversing the pressure and wind pattern.
Northeasterlies cross the Bay of Bengal and gain moisture.
Important for Tamil Nadu, south Andhra Pradesh and parts of Sri Lanka.
It compensates for relatively lower southwest-monsoon rainfall in parts of southeastern India.

2. ITCZ: The Dynamic Core of Monsoon Circulation

The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt near the Equator where winds from the two hemispheres converge and warm air rises.

Summer heating

→

ITCZ shifts north

→

Monsoon trough

→

Convection & clouds

→

Southwest Monsoon

In July, the ITCZ can reach the Gangetic plains. Its northward movement helps draw moisture-bearing winds toward India.

Its southward retreat around October is associated with reversal toward the northeast monsoon.

3. ENSO and Monsoon Variability

El Niño

Associated with unusual warming of the central/eastern equatorial Pacific.
Often linked with a weaker or delayed Indian southwest monsoon.
Since 1950, 16 El Niño years occurred; 7 were associated with below-normal Indian monsoon rainfall.

La Niña

Associated with cooling of the central/eastern Pacific.
Generally linked with normal to above-normal monsoon rainfall in India.
Excess rainfall can also increase flood, crop and livestock risks.

4. Spatial Pattern of Rainfall

India's rainfall averages about 125 cm annually but varies sharply across space because of monsoon pathways, relief and rain-shadow effects.

Western coast & NE

>400 cm

Western Rajasthan etc.

<60 cm

Leh/Ladakh

Very low

Orographic rainfall: Moist winds rise over the Western Ghats and northeastern hills, cool and condense, producing heavy rainfall.

Areas east of the Sahyadris experience rain-shadow conditions.

5. 2024 Southwest Monsoon: Regional Performance

India received 934.8 mm during June–September 2024 against an LPA of 868.6 mm, i.e. 108% of LPA.

East & Northeast

86%

Northwest

107%

Central

119%

South Peninsula

114%

LPA = Long Period Average.

6. 2024 Rainfall by Month

June

89%

July

109%

August

115%

September

112%

June was below normal, while rainfall strengthened in July–September, with August at 115% of LPA.

7. Monsoon Variability Over Time

Sub-seasonal, interannual, decadal and longer-term variability are observed. Active–break cycles are an important sub-seasonal feature.

2015

16

2016

10

2018

11

2019

3

2020–23

5–7

2024

3

8. Monsoon–Economy Linkages

Agriculture

Nearly 64% of Indians are stated to depend on agriculture; only about 55% of net sown area is irrigated in the source.

Water Security

Monsoon rainfall replenishes rivers, lakes, groundwater and reservoirs, shaping drinking-water and irrigation availability.

Energy

Good monsoon conditions support reservoir storage and hydropower generation.

Rural Demand

A good monsoon can raise agricultural output, rural incomes and consumption.

Food Security

Rainfall performance influences crop output and consequently food availability and prices.

Hazards

Delayed or uneven rainfall can produce droughts, floods and soil erosion.

9. Climate Change and the Indian Monsoon

Climate change

→

Changing rainfall distribution

→

Longer dry spells

+

More intense wet spells

→

Higher adaptation burden

The source does not identify a clear long-term national-average trend in total rainfall, but reports substantial spatial differences.
It reports declining monsoon rainfall in parts of Kerala, Northeast India and East Central India, while North Karnataka, Maharashtra and Rajasthan show increases.
Extreme daily rainfall events above 150 mm have increased; central India saw an increase of around 75% between 1950 and 2015.
Dry spells during the summer monsoon became about 27% more common during 1981–2011 compared with 1951–1980.
Nearly half of seasonal rainfall can occur in 20–30 hours, intensifying flood and runoff risks despite longer dry intervals.
July rainfall is reported as declining while September is becoming wetter, alongside shifts in monsoon onset and withdrawal in different regions.

10. Climate Change → Agricultural Risk

Long dry spell

→

Moisture stress

→

Yield risk

Short intense rainfall

→

Runoff / erosion

→

Waterlogging & crop loss

11. IMD: Forecasting and Early Warning

India Meteorological Department (IMD), established in 1875 under the Ministry of Earth Sciences, provides weather and climate services for agriculture, disaster management, aviation and public safety.

Seasonal Forecast Cycle

Mid-April: broad southwest monsoon rainfall forecast.
Mid-May: prediction of southwest monsoon onset date.
End-June: updated seasonal forecast with regional/month-specific information.
Forecasts also support northeast monsoon and winter-rain assessments for relevant users.

2021–24 Forecast Record

Year	Forecast	Actual	Status
2021	101%	100%	Accurate
2022	103%	106%	Accurate
2023	96%	95%	Accurate
2024	106%	108%	Accurate

Source criterion: forecast within ±5% of LPA.

12. Mission Mausam

Approved on 11 September 2024 as a Central Sector Scheme, Mission Mausam seeks to make Bharat “weather-ready and climate-smart” through better observation, modelling, forecasting and decision support.

OBSERVE_All

Collects and monitors weather data.

DEVELOP

Builds next-generation Earth System Models.

IMPACT

Strengthens severe-weather early warnings and research-to-practice links.

FRONTIER

Develops new observation and measurement technologies.

ATCOMP

Supports air-quality tracking and pollution management.

DECIDE

Builds decision-support systems for agriculture, water and energy.

Weather_MOD

Explores weather-modification strategies such as rain enhancement or fog control.

LEAD

Builds capacity and improves dissemination of weather information.

NEAT

Promotes partnerships with private firms for observation systems.

Implementation is described in two phases: 2024–2026 and continuation from 2026–2031. The source states that ACROSS is merged into Mission Mausam.

13. Technological Capacity: Selected Indicators

Doppler radars

15 → 39

Automatic Rain Gauges

1350 → 1382

DRMS stations

3955 → 5896

Values compare 2014 and 2023 as stated in the source; bar lengths are visual aids.

14. Lightning as an Emerging Monsoon Hazard

The source notes that lightning remains a major weather-related hazard during monsoon months and that recent data indicate a shift in hotspots, with eastern and central India witnessing more frequent lightning events.

Gujarat, Rajasthan and Punjab recorded increases in the cited discussion.

UPSC Mains Answer Framework

Question: “The Indian monsoon is simultaneously an economic lifeline and a source of increasing climatic risk.” Discuss the statement with reference to changing rainfall patterns and India's preparedness.

Introduction

Define the monsoon as a seasonal reversal of winds and establish its importance through its links with agriculture, water resources, hydropower and rural livelihoods.

Body I — Why the Monsoon Matters

Agriculture and food security.
Groundwater, reservoirs and drinking-water security.
Hydropower and rural demand.
Ecological and socio-cultural significance.

Body II — Why Variability is Rising in Policy Significance

Spatial and temporal variability.
Longer dry spells and intense rainfall events.
Flood–drought coexistence and soil erosion.
Changing onset, withdrawal and intra-seasonal distribution.

Body III — Institutional and Technological Response

IMD seasonal forecasting and early warnings.
Doppler weather radar and ground observation expansion.
Mission Mausam and AI/ML-enabled forecasting.
Decision-support systems for agriculture, water and energy.

Way Forward

Climate-resilient agriculture and irrigation expansion.
District-level impact-based forecasting and early-warning dissemination.
Rainwater harvesting, watershed management and reservoir optimisation.
Weather-indexed risk management and resilient infrastructure.
Greater use of high-resolution models, radar, satellites and AI/ML.

Quick Recall

1. What does ITCZ contribute to the Indian Monsoon?

Its north–south seasonal migration helps organise the monsoon trough, convection, moisture inflow and seasonal wind reversal.

2. Why is rainfall distribution more important than aggregate rainfall alone?

Because intense rainfall over short periods can coexist with prolonged dry spells, creating flood, runoff, soil-erosion and crop-moisture risks even when seasonal totals appear adequate.

3. How can Mission Mausam strengthen climate resilience?

Through improved observation, modelling, severe-weather warnings, sectoral decision support, new technologies and stronger dissemination of weather information.

Conclusion

The monsoon should be viewed not merely as a rainfall phenomenon but as a system linking climate, agriculture, water, energy, livelihoods and disaster risk . The policy objective is therefore to move from rainfall forecasting alone toward impact-based, climate-resilient and locally actionable weather governance .