Indian Monsoon: At a Glance

Indian Monsoon: At a Glance

Introduction

The monsoon is more than just a season of rain for India as this unique climate system is a lifeline for the people of the country. Monsoon rains are critical for the agricultural sector with productivity and food grain prices closely linked to a good monsoon. They are crucial for replenishing the country’s water reserves, and for generation of hydro- electricity. The seasonal reversal of winds are what we call monsoon. A good monsoon has always meant general prosperity and well-being and bad monsoon has meant distress. 

What is Monsoon?

The word monsoon is derived from the Arabic word Mausim, meaning “season.” It refers to a seasonal reversal of winds caused by differential heating, and consequent pressure difference between sea and land.

During summer the land heats up faster than the surrounding sea. The hot air over the land rises, creating low pressure. This attracts the relatively cooler, moisture laden air from the high-pressure areas over the sea to blow towards land as monsoon winds, causing widespread rains when they reach the land and encounter mountain ranges.

The reverse happens in winter, with winds blowing from the cooler land areas towards sea as retreating monsoon.

Types of Monsoon

Each year, India experiences two distinct monsoons namely Southwest Monsoon and the Northeast Monsoon.

Southwest Monsoon (June to September)

Near about 75 per cent of India’s total rainfall comes during this season making it essential for irrigation, drinking water, and even electricity generation through hydropower. Therefore, southwest monsoon is India’s main rainy season and a lifeline for the country’s economy and ecology. It supports farming, fills rivers and lakes, and recharges groundwater.

Usually it begins in early June when the monsoon winds reach Kerala. Over the next few weeks, these winds spread across the entire country. By the middle of July, most of India is covered. The process starts because land heats up faster than the sea during summer. This creates low pressure over northern and central India. At the same time, the Indian Ocean stays cooler, leading to higher pressure over the sea. Moist winds flow from the ocean to the land, bringing rain.

These winds are called southwesterlies because they blow from the southwest. They split into two branches. One travels along the Arabian Sea and brings rain to the western coast and central India. The other moves across the Bay of Bengal and reaches eastern and northeastern parts of the country. As these winds hit mountain ranges like the Western Ghats and the Himalayas, they rise, cool, and release rain. The monsoon weather systems forming over the warm Bay of Bengal bring plenty of rains when they move across northern parts of the country. This monsoon is especially important for crops like rice, cotton, and sugarcane. A delay or failure in this season can affect food supply, livelihoods, and the wider economy.

Northeast Monsoon (October to December)

As the southwest monsoon begins to fade, the northeast monsoon sets in by October. This is also called the retreating monsoon. It is shorter and less widespread but still important, especially for southern India.

By October, the land starts to cool faster than the ocean. This creates a high-pressure area over the Indian subcontinent and a low-pressure area over the surrounding seas. The direction of wind flow reverses. Now, winds blow from land to sea. These are called northeasterlies.

Since these winds pass over the Bay of Bengal before reaching the southeastern coast, they pick up some moisture. As they reach Tamil Nadu, south Andhra Pradesh and parts of Sri Lanka, they provide abundant moisture for rainfall activity. This rain is crucial for regions like Tamil Nadu that do not receive much during the southwest monsoon. Weather systems forming over south Bay of Bengal bring abundant rainfall over south Peninsula.

Factors Affecting Indian Monsoon

The Indian monsoon is a complex weather system shaped by many natural forces. These forces decide when the rains arrive, how much rain falls, and how long the season lasts. While some factors work at a global scale, others are more local. Together, they guide the flow of winds, the rise of clouds, and the spread of rainfall across the country.

Some of the most notable factors that affect Indian monsoon include:

1. Inter-Tropical Convergence Zone, or ITCZ: It plays a major role in shaping the Indian monsoon. It is a narrow belt near the Equator where winds from the northern and southern hemispheres meet. This zone is known for low pressure and rising warm air, which often leads to cloud formation and rain. During the summer months, the ITCZ moves northward, following the Sun. In July, it can reach as far as the Gangetic plains in northern India. This movement is important because it pulls in moist winds from the oceans towards the land. These winds become part of the southwest monsoon. As the ITCZ shifts north, it creates a zone of strong convection. That means warm air rises quickly, forms clouds, and brings rain. This low-pressure area is sometimes called the monsoon troughwhen it forms over land. It is especially active during the peak monsoon months and helps produce long spells of rain in many parts of the country. The ITCZ also explains why the monsoon arrives in India in early June. When the Sun starts heating the Indian landmass, the ITCZ begins its northward journey. This change in its position helps draw in the trade winds from the southern hemisphere. After crossing the Equator, these winds bend due to the Earth’s rotation and arrive in India from the southwest. These are the southwest monsoon winds. Later in the year, around October, the ITCZ starts moving south again. As it retreats, the winds reverse. Now they blow from the northeast, leading to the start of the northeast monsoon. This shows how closely the Indian monsoon is linked to the yearly movement of the ITCZ. In short, the ITCZ acts like a switch that helps turn the monsoon on and off. Its position decides the direction of winds, the spread of rain, and the arrival and withdrawal of the monsoon across the country.

2. El Niño Effect: is a natural climate event that forms in the Pacific Ocean but influences weather patterns across the world, including India. It happens when warm water builds up along the coast of South America, especially near Peru and eastern parts of the equatorial Pacific. This rise in ocean temperature changes the movement of air and clouds across the globe, which can disturb regular wind patterns. For India, this often results in a weak or delayed monsoon season. During an El Niño year, the usual flow of moist winds towards India is disrupted. This change reduces the amount of rainfall India receives between June and September. In the past, strong El Niño events have led to serious drops in rainfall, late arrival of the monsoon, and dry spells in key agricultural states. To reduce the risks, Indian weather agencies monitor ocean temperatures and pressure changes closely. The India Meteorological Department uses these signals to forecast long-term monsoon patterns and issue early warnings. This helps farmers, governments, and disaster relief agencies prepare in advance. Since 1950, there have been 16 El Niño years, out of which 7 years had impacted Indian monsoon rainfall when rainfall was below normal.

3. La Niña and the Indian Monsoon: La Ninais a natural climate pattern that causes the central and eastern parts of the Pacific Ocean to cool more than usual. This change in ocean temperature affects global weather, including India’s monsoon. During La Niña years, most regions in India receive normal to above-normal rainfall in the southwest monsoon season. This is especially helpful for rainfed farming and water storage. However, the excessive rain can sometimes lead to floods, damage to crops, and the loss of livestock in certain areas. Unlike El Niño, which often weakens the Indian monsoon and leads to dry conditions, La Niña usually strengthens it. While El Niño is linked to warm ocean waters and weaker monsoon winds, La Niña is marked by cooler waters and stronger moisture-bearing winds towards India. In simple terms, El Niño tends to bring less rain and more uncertainty, while La Niña often brings heavier rainfall. Also, below-normal temperatures are generally observed during the winter season during the La Niña years.

Distribution of Rainfall in India

Rainfall in India is not the same everywhere. Some regions receive very heavy rain, while others remain mostly dry. The average annual rainfall in India is about 125 cm, but it has great spatial variations. This uneven pattern is linked to the path of the monsoon winds and the shape of the land. As monsoon winds vary from year to year, the rainfall is not always the same. This variation is called rainfall variability.  Indian monsoon exhibits a wide spectrum of variability, on diurnal, synoptic, sub-seasonal, interannual, decadal and centennial time scales. The active-break cycles of monsoon rainfall represent the sub-seasonal variability of the Indian monsoon. A significant fraction of the interannual variations of monsoon rainfall is associated with tropical and subtropical ocean climate.

The western coast and parts of Northeast India get the highest rainfall. These areas receive more than 400 centimetres of rain every year. The winds from the Arabian Sea hit the Western Ghats, forcing the air to rise. As the air rises, it cools and forms clouds, leading to heavy rain. This is known as orographic rainfall and is common along mountain slopes. Similarly, the hills in the Northeast act like barriers and bring large amounts of rain to places like Meghalaya and Arunachal Pradesh.

In contrast, parts of western Rajasthan and nearby regions in Gujarat, Haryana and Punjab get very little rain. These areas receive less than 60 centimetres of rain annually. The Deccan plateau and areas east of the Sahyadri hills also get low rainfall. These places lie in the rain shadow region, meaning the hills block the rain-bearing winds. Leh, in Ladakh, is another area with very low rainfall due to its high altitude and cold desert climate. Most other parts of India receive moderate rainfall. Snowfall is limited to the Himalayan region.

Why Indian Monsoon is so important?

The monsoon is central to India’s economy, especially its agricultural sector. With a large part of the population relying on farming, the success or failure of the monsoon can shape the country’s overall economic health.

• Nearly 64 per cent of Indians depend on agriculture, which mainly relies on the southwest monsoon.
• Only about 55 per cent of India’s net sown area is covered by irrigation. The rest depends on rain-fed systems, which makes a large part of the country’s farmland highly vulnerable to changes in rainfall patterns.
• Good monsoon raises agricultural production, aids GDP growth, drives up rural earning and consumption.
• Most parts of the country stay warm enough for farming throughout the year, except the Himalayan region.
• Different rainfall patterns across regions allow a wide variety of crops to be grown.
• Uneven or late rainfall often causes floods or droughts, affecting both crops and rural incomes.
• Areas without proper irrigation suffer the most when the monsoon is weak or delayed.
• Sudden and intense rain can lead to soil erosion, harming the fertility of land.
• Winter rain in north India, brought by western disturbances, is helpful for wheat and other rabi crops.
• Local climate, shaped by the monsoon, also influences food habits, clothing styles and types of houses across India.

The monsoon is not just a weather pattern; it is the heartbeat of India’s economy, environment and everyday life. From sowing seeds in rural fields to powering cities through hydroelectricity, its influence is vast and far-reaching. While the science behind the monsoon has grown more precise over the years, its unpredictable nature still reminds us of the delicate balance between nature and human activity.

Accurate forecasting, early warning systems and scientific missions like Mission Mausam are helping the country prepare better for the changes each season may bring. At the same time, rising challenges such as climate change and extreme weather events require continued investment in research, technology and public awareness.

Mission Mausam

Mission Mausam is a new Central Sector Scheme approved by the Cabinet on 11 September 2024. Its aim is to reduce the impact of extreme weather events caused by climate change and build stronger, more resilient communities. The broader goal is to make Bharat a “weather-ready and climate-smart” nation.

The mission focuses on improving how India monitors and predicts weather. This will be done by using advanced tools such as high-resolution weather radars, satellites with better instruments, and next-generation computing systems. It also plans to use artificial intelligence and machine learning to improve forecasting.

To carry out its vision, Mission Mausam has been organised into nine verticals, each led by institutes under the Ministry of Earth Sciences. These verticals will work together to improve real-time weather and climate services across the country and nearby regions.

Nine Verticals of Mission Mausam:

1. OBSERVE_All: Collects and monitors weather data for forecasting and decision-making.
2. DEVELOP: Works on building next-generation Earth System Models for better predictions.
3. IMPACT: Focuses on early warnings for severe weather events and turning research into practice.
4. FRONTIER: Builds new technologies for observing and measuring weather.
5. ATCOMP: Develops tools for air quality tracking and pollution management.
6. DECIDE: Designs decision-support systems for sectors like agriculture, water, and energy.
7. Weather_MOD: Prepares strategies for weather modification like rain enhancement or fog control.
8. LEAD: Builds capacity and improves the way weather updates are shared with people.
9. NEAT: Encourages partnerships with private firms for improved observation systems.

Many parts of Mission Mausam build upon and improve the existing ACROSS sub-scheme under the PRITHVI programme. As a result, ACROSS will now be merged with this new mission. Mission Mausam will be implemented in two phases: from 2024 to 2026, and continued from 2026 to 2031 in the next funding cycle.

See Also…..
CROPPING SEASONS OF INDIA
Cropping Systems- Meaning Types & Advantages
WEATHER CLIMATE AND SEASON