Climates of India

Class 07 Social Science

Weather is what we experience every hour or day. It might be raining, or there could be bright sunshine, a lot of wind, etc. The weather keeps changing. Climate is the pattern of weather an area or a region experiences over a long period of time - several decades at least. This pattern varies from region to region.

Seasons

Seasons occur as the Earth revolves around the Sun. Each season lasts for a few months and recurs every year. There are several seasons in the year - spring, summer, monsoon, autumn and winter - that occur in a cycle.

The weather changes with the season, that is, it can be dry and hot in the summer months, or humid and rainy during the monsoon. Further, the pattern of seasons in a region is closely connected with the climate. There are four main seasons across most regions of the world - spring, summer, autumn and winter. However, India receives rainfall during a specific period of the year - the ‘rainy season’ or monsoon - along with the other four.

Weather is what we experience from day to day - windy, rainy, hot, dry, etc. Seasons recur every year and the weather of a place is different in every season. Climate is the long-term pattern in a particular region. There are many types of climates in the world.

Types of Climates in India

In the north, the Himalayan mountains have an alpine climate with cold, snowy winters and cool summers. Lower in the Himalayas, and in many hilly areas of India, the climate is often said to be temperate, as the winters are moderately cold and the summers not too hot.
In the northern plains, the climate is subtropical, with very hot summers and cold winters. This is where most of India’s wheat is grown.
In the west, the Thar Desert has an arid climate featuring extremely hot days, cool nights, and very little rainfall. People have had to develop unique ways to collect and save water.
The western coastal strip receives heavy rainfall during monsoon months, creating a tropical wet climate, which is favourable to the growing of rice and spices.
The central Deccan Plateau has a semi-arid climate with hot summers, mild winters and moderate rainfall during the rainy season.
Eastern India and the southern peninsula experience a tropical climate with a mild winter and distinct wet and dry periods controlled by monsoon winds.

Factors Determining the Climate

1. Latitude

Places near the Equator, that is, at low latitudes, are warmer, while those near the poles (high latitudes) are colder. This happens due to the angle at which the sun’s rays hit a particular area. At the Equator, the rays are nearly perpendicular, and so all their energy is focused on a smaller area of the Earth’s surface. In the polar regions, the rays are inclined or oblique, and the energy is distributed over a larger surface.

Moreover, they have to pass through more of the Earth’s atmosphere, which further dissipates their energy. As a result, the polar regions receive less heat than the equatorial zone. Kanniyakumari and the Nicobar Islands being close to the Equator are warm or hot almost throughout the year, whereas places in the north, such as Srinagar, are much cooler.

2. Altitude

The temperature decreases as the altitude increases.

The atmospheric pressure, and therefore the air density, decreases as the altitude increases, and as the air gets less dense, it gets cooler. The sun heats the surface of the Earth, and so the farther away from the surface, the less hot the air will be. The Himalayas are so high that many peaks maintain a temperature below water’s freezing point, keeping them covered in snow.

3. Proximity to the Sea

Temperatures in coastal areas do not vary much. The summers are not too hot and the winters are not too cold. That is because the sea acts as a moderator for the temperature. As you move inland from the coast, the temperatures get more extreme - summer temperatures will be higher and winter temperatures lower.

For example, Mumbai and Nagpur are located at a similar latitude, but Mumbai, being near the sea, has cooler summers (around 32°C) and milder winters (around 18°C), while Nagpur, away from the coast, experiences up to 44°C in summer and about 10°C in winter.

4. Winds

Wind can move masses of warmer or cooler air. States like Punjab, Haryana, Rajasthan and Madhya Pradesh often receive winds blowing from the west. Having travelled over the deserts of Arabia to Afghanistan, they bring dry and hot air that causes severe heat waves in summer. In winter cold winds from across the Himalayas creep into the Himalayan foothills, resulting in cold waves.

Winds affect not only temperature, but also humidity, and in turn, precipitation. Winds coming from the sea bring moisture over the land, which may result in rainfall.

5. Topography

The topography of a region also plays an important role in determining its climate. For example, the Himalayas and the Karakoram ranges protect the Indian subcontinent from the winds of the cold deserts of Central Asia.

The nearly flat topography of the Thar desert has nothing to protect it from hot and dry winds.

The Monsoons

The monsoon season is central to life in India. During the monsoon months, the rivers fill up, the soil is soaked with water, crops grow and life thrives.

As summer begins, the Asian landmass heats up, creating a powerful low-pressure system over it. Since air always flows from high pressure to low pressure, winds are drawn from the cooler, high-pressure ocean towards the hot land. These ocean winds carry moisture that condenses over the warmer land and falls in the form of heavy monsoon rains.

The pattern reverses in winter, when the landmass cools down more rapidly than the ocean. Now the land has a high-pressure system while the ocean remains warmer with relatively lower pressure. This causes the winds to blow in the opposite direction - from the land towards the ocean - bringing dry conditions to much of Asia.

The monsoon rains typically advance from the southern tip of India in early June, moving northward over several weeks until they cover the entire subcontinent by mid-July. It is not a smooth progression, though the Western Ghats act as a natural barrier; their western slopes receive much rainfall, while the Deccan plateau to the east receive less, and often with interruptions. This is commonly called the summer or southwest monsoon.

As winter approaches, the winds reverse and blow from the land to the ocean. These are dry winds that bring cold weather to south India, but a part of them, passing over the Bay of Bengal, collect some moisture and bring rainfall to parts of east and south India. This is called the winter or northeast monsoon.

Climates and Disasters

India’s diverse weather patterns can bring about extreme conditions such as cyclones, floods, landslides and other such climate-related disasters.

1. Cyclones

Every year, the Indian coastline, especially the eastern coast, witness several cyclones. In past years, some of them have been highly destructive, resulting in the loss of human and animal life, damaging property and infrastructure, uprooting trees and causing soil erosion.

The atmospheric pressure near the sea becomes lower than the surrounding areas, creating a low-pressure system. This invites the air from surrounding areas to come into the low-pressure area, and the air from the sea moves in, bringing with it moisture and rain. When the low-pressure system is intense and the wind speeds are high, this may result in a cyclone.

As winds collect moisture, they form clouds and rotate inwards towards the centre of the depression. This centre, which is cloudless, is called ‘the eye of the cyclone’.

2. Floods

A flood occurs when water overflows into normally dry land. This could be due to heavy rainfall generating huge run-off water that the land cannot absorb, or due to excessive accumulation of water in bodies like rivers and lakes, until the water overflows or their banks are breached. Floods occur frequently during the monsoons. States such as Uttar Pradesh, Bihar, Kerala, Andhra Pradesh and Assam are particularly vulnerable to floods.

In the Himalayan regions, floods occur when glacial lakes overflow. Glacial lakes form a barrier of rocks and ice to hold their water, which often comes from melting glaciers. If the glaciers melt too fast or if there is too much rainfall, the build-up of pressure can cause the water to break through the barrier - this is called a glacial burst and it often has devastating consequences for people and property.

Many cities experience flooding when there is heavy rainfall. This may be due to an overburdened drainage system or poorly planned construction encroaching on the waterways and blocking the flow of water. Besides, urban surfaces of concrete or asphalt do not allow water to be absorbed by the earth.

3. Landslides

A landslide is the sudden collapse of rock, soil, or debris, often triggered by heavy rain, earthquakes or volcanic activity. Landslides are common in hilly and mountainous regions such as Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh, as well as the Western Ghats and hilly regions. These events often occur during the monsoon.

In those regions, the chances of landslides have increased due to human activities such as the cutting down of forests, building infrastructure without following approved methods and the construction of too many buildings that block the natural flow of water.

4. Forest Fires

Forest fires are uncontrolled fires that spread rapidly across vegetation, often fuelled by dry climatic conditions, droughts or high winds. Human carelessness is another frequent cause.

Forest fires are common in states with large forested or grassland areas such as Uttarakhand, Himachal Pradesh, Madhya Pradesh and Chhattisgarh, as well as mountain ranges such as the Western Ghats. Apart from destroying large areas of forest, fires harm wildlife, degrade the ecosystem, spoil the air quality and displace local communities. The consequences are therefore both environmental and economic.

Climate Change

Climate change refers to significant, long-term changes in the climate. This may be on the scale of the planet or on a regional scale, and it involves shifts in temperature, precipitation and weather events.

In past millennia, natural processes drove climate change. Since the 19th century, however, climate change has been largely driven by human activities, particularly the burning of fossil fuels, deforestation, environmentally harmful industrial practices, and production and patterns of excessive or wasteful consumption.

Burning of Fossil Fuels

In the Earth’s natural carbon cycle, carbon dioxide (CO₂) and other gases are released gradually into the atmosphere and trap heat from the Sun. This natural ‘greenhouse effect’ warms Earth enough to support life. However, human activities like industry, transportation, and agriculture have released enormous amounts of these ‘greenhouse gases’ in just a few centuries. This sudden increase traps extra heat, causing rapid global warming and disrupting the climate patterns that plants, animals, and human societies have adapted to over thousands of years.