Climate Notes in English Class 11 Geography Chapter-4 Book-India Physical Environment

 

Uniformity and diversity in monsoon climate

India's climate is primarily monsoonal, which forms the basis of the uniformity of weather across the country. However, there are distinct regional variations, which emerge in the form of differences in temperature, rainfall and winds.

• Variation in Temperature: Summers in Rajasthan can reach 50°C, while winters in Ladakh can drop to -45°C. The temperature difference is minimal in coastal areas, but in desert areas it varies considerably from day to night.

• Variation in rainfall: Somewhere like Cherrapunji, it rains upto 1100 cm, whereas some parts of Rajasthan receive less than 10 cm.

• Monsoon Effect: Monsoon is the mainstay of India's climate, but its regional variations make it complex and unique.

Factors affecting the climate of India

• Latitude: Due to the Tropic of Cancer passing through India, there is a difference in the climate of the northern and southern parts of the country. South India, being located in the tropics, maintains a stable and warm climate, while North India has cold winters and hot summers.

• Himalayan Mountains: The Himalayan Mountains play the role of a climatic divide in northern India. These high mountains provide protection to the subcontinent by blocking the cold northern winds. The Himalayas block the monsoon winds, cause rainfall and create rivers flowing across the country.

• Distribution of water and land: Coastal areas have a stable temperature because they are surrounded by the sea. The difference in the heating rate of land and sea is the basis of the monsoon system, which is important for agriculture and water supply.

• Distance from the coast: Coastal areas have stable and even climate, like Mumbai, while interior areas have sharp variations in temperature, like Delhi and Kanpur.

• Altitude above sea level: Temperatures drop with altitude. For example, Darjeeling has cold weather, while Agra, located at the same latitude, has a hot climate.

• Relief (mountains and slopes): Windward slopes, such as the Western Ghats, receive heavy rainfall, while leeward slopes, such as the Southern Plateau, receive less rainfall. This shows the influence of geographic structure on climate.

Nature of Indian Monsoon

The Indian monsoon is an important part of our climate, but understanding it fully is still a challenge. Scientists have made many efforts to understand it, but a precise theory has not been developed yet. In recent years, new information has been obtained by looking at it from a global perspective.

Onset and Progress of Monsoon:

• The monsoon enters the southern coast of India (Kerala) around June.

• It slowly moves north and west, bringing rainfall across the country.

onset of monsoon

1. The main cause of monsoon

• The Indian monsoon is caused by the differential heating of land and sea. This process attracts monsoon winds towards India during the summer months.

2. Process of monsoon formation

• In April and May, the intense heat over northwest India due to direct sunlight over the Tropic of Cancer leads to the formation of a low pressure area.

• The Indian Ocean remains cold, which causes winds to be pulled northwards from near the equator.

• These south-eastern trade winds change into south-west monsoons after crossing the equator.

• These moist and warm winds bring heavy rainfall in India.

• The shift of the westerly jet stream over the Himalayas and the development of the easterly jet stream over South India play an important role in the "burst" of the monsoon.

3. Entry of monsoon in India

• The southwest monsoon enters the Kerala coast in the first week of June.

• It moves rapidly and reaches Mumbai and Kolkata by 10-13 June.

• By mid-July the monsoon covers all of India, bringing widespread rainfall across the country.

Break in Monsoon

When rains for a few days during the southwest monsoon are followed by a sudden stoppage of rain for a week or two or more, it is called a monsoon break. It happens for different reasons in different places:

• North India: Rainfall breaks occur when tropical cyclones weaken or the Inter Tropical Convergence Zone (ITCZ) changes its position.

• West Coast: Here the monsoon break occurs when the moisture laden winds from the sea start blowing parallel to the coast.

• Rajasthan: The monsoon stops here when warm air causes temperature inversion at lower levels, which prevents moist air from rising and causing no rain.

Retreat of Monsoon

When the monsoon winds start retreating, it is called withdrawal of monsoon.

• When does it start? :  The monsoon starts retreating from northwest India in early September.

• When does it end? :  By mid-October it disappears from all of India except South India.

• Rains in Tamil Nadu:  The retreating winds carry moisture from the Bay of Bengal and become the north-east monsoon, which brings rain to Tamil Nadu.

Seasonal Cycle

The climate of India is divided into four main seasons:

Winter: characteristics and effects

1. Temperature

• Winter lasts from mid-November to February in India.

• January and February are the coldest months in North India, with average temperatures below 21°C.

• Temperatures may occasionally drop to 0°C in Punjab and Rajasthan, while snowfall in the Himalayan region is the major cause of cold winds.

• In the coastal areas of South India, the temperature remains stable due to the influence of the ocean, for example, Thiruvananthapuram has an average temperature of 31°C.

2. Wind and air pressure

• A high pressure area forms in the northern plains, due to which winds blow from the north-west towards the Indian Ocean.

• In the Ganga valley these winds blow in the western and north-western direction, whereas in the Bay of Bengal they turn towards the north-eastern direction.

3. Rain

Most of India does not receive rain during winter, but there are exceptions in some areas:

• Northwest India: Cyclones from the Mediterranean bring light rains and snow in the Himalayas, which is beneficial for Rabi crops.

• North-East India: Light rain occurs over Arunachal Pradesh and Assam.

• South India: The north-east monsoon brings rain to Tamil Nadu and Andhra Pradesh.

Summer: characteristics and influences

1. Temperature

• Summer lasts from March to June in India.

• In North India, the temperature starts rising from March and can reach 38°C to 48°C in April-May. Areas like Rajasthan and Punjab remain the hottest.

• In South India, due to the influence of the ocean, temperatures are relatively mild (26°C to 32°C), while in the hills of the Western Ghats it may drop below 25°C.

• The temperature remains constant in coastal areas because the isotherms are parallel to the coast.

2. Air pressure and winds

• Due to the decrease in air pressure in northern India during summer, a low pressure area is formed from the Thar Desert to Bihar and Chhattisgarh.

• This drop in pressure attracts southwesterly winds, which signal the arrival of the monsoon. By June these winds start the rainy season.

3. Local Events

• Loo: Hot and dry winds blow across North India during May-June.

• Dust Storms: Evening dust storms over Punjab, Haryana and Uttar Pradesh bring light rain and cool winds.

• Kal Baisakhi: Local storms with strong winds, rain and sometimes hail occur in Bengal and Bihar.

South-west monsoon: Characteristics of the rainy season

• Importance of Monsoon: The southwest monsoon is the most important season in India, bringing rain throughout the country from June to July and playing a vital role in agriculture and water supply.

• Monsoon Process: High temperatures over northwest India in May create a low pressure area, which attracts winds from the Indian Ocean.

• The south-eastern trade winds cross the equator and enter the Arabian Sea and the Bay of Bengal.

• While passing over the warm sea, these winds become filled with moisture and turn towards the south-western direction.

• The monsoon arrives in a "burst", with rain accompanied by thunder and lightning.

Branches of the monsoon

• Arabian Sea branch: Brings heavy rains to coastal areas like Kerala, Karnataka, Goa, and Maharashtra.

• Bay of Bengal branch: Brings widespread rainfall to Bengal, north-east India and the foothills of the Himalayas.

Spread of the monsoon

• The monsoon starts in Kerala in the first week of June and spreads across India by July.

• With this, the day temperature drops by 5°C to 8°C, providing relief from the heat.

Monsoon winds of Arabian Sea 

The monsoon winds blowing from the Arabian Sea bring rain to India in three branches:

• Western Ghats branch: It brings heavy rainfall up to 250-400 cm on the slopes of the Western Ghats. After crossing the Ghats, the rain-shadow areas receive less rainfall, like Pune and Bangalore.

• Narmada-Tapi Valley Branch: It brings up to 15 cm of rain in the Narmada and Tapi valleys. It joins the Bay of Bengal branch in the Ganges plain and increases the rainfall.

• Saurashtra-Kutch branch: Saurashtra and Kutch receive scanty rainfall. Moves along the Aravallis into Punjab-Haryana and brings heavy rains to the Himalayan regions, especially Dharamsala.

Monsoon winds of the Bay of Bengal

The monsoon winds from the Bay of Bengal bring the main rainfall to the eastern and north-eastern parts of India.

Directions and travel:

• Enter India from the coasts of Myanmar and Bangladesh.

• The first branch goes from the Gangetic plain to Punjab.

• The second branch causes rainfall in the Brahmaputra valley and the north-east.

• Mawsynram receives heavy rainfall after colliding with the Khasi-Garo hills of Meghalaya.

Reasons for less rain in Tamil Nadu:

• The winds blow parallel to the coast.

• The region falls in the rain shadow of the southwest monsoon.

retreating monsoon season

October and November are called the retreating monsoon season. During this time the southwest monsoon gradually weakens, and seasonal changes occur in different parts of India.

1. Withdrawal of monsoon

• With the southward movement of the Sun in September, the low pressure area of ​​the Ganga plain starts moving towards the south, due to which the monsoon starts returning from Rajasthan. 

• By October the monsoon retreats from the western Gangetic plains, Gujarat and central India and reaches the northern parts of the Bay of Bengal. 

• During November–December it moves towards Tamil Nadu and Karnataka and withdraws completely from the peninsula by mid-December.

2. Signs of the weather

• During the retreat of monsoon in October, the sky remains clear but the temperature rises and hot and humid weather is experienced, which is called the 'heat of Kartik month'. 

• By the end of October, temperatures begin to fall rapidly in northern India, while eastern parts of the peninsula, such as Tamil Nadu and Andhra Pradesh, receive rain due to the northeast monsoon.

3. Cyclonic rainfall

• Cyclonic depressions form in the Bay of Bengal during October–November, bringing heavy rainfall and devastating effects on the eastern coast of the southern peninsula, especially the Coromandel coast. 

• These storms affect the delta regions of the Godavari, Krishna and other rivers as well as the coastal areas of West Bengal, Bangladesh and Myanmar. 

• At the same time, relatively fewer cyclones form in the Arabian Sea and their impact remains limited.

Traditional seasons of India

Six Seasons in Indian Tradition

According to the ancient tradition in India, the year has been divided into six seasons on the basis of two months each.

• North and Central India: Here people follow these seasons based on their experience and old knowledge.

• South India: The seasons here are slightly different from those of North and Central India.

Distribution of rainfall 

The average annual rainfall in India is about 125 cm, but there are considerable variations regionally. Let us understand this simply:

1. Areas with high rainfall (more than 200 cm)

• The major places with heavy rainfall in India include the west coast and Western Ghats, the sub-Himalayan region of the north-east (Brahmaputra Valley), and the Khasi and Jaintia Hills of Meghalaya. 

• In particular, Mawsynram and Cherrapunji located in Meghalaya are famous as the rainiest places in the world, where annual rainfall is recorded to be the highest in the world.

2. Areas with moderate rainfall (100-200 cm)

• Areas with moderate rainfall in India include the southern part of Gujarat and eastern Tamil Nadu. Apart from this, Jharkhand, Odisha, Bihar and eastern Madhya Pradesh also experience moderate rainfall. 

• The sub-Himalayan Gangetic plains to the north, the Cachar valley and Manipur also fall in this category, where rainfall is sufficient to sustain the agriculture and ecology of these areas.

3. Areas with low rainfall (50-100 cm)

• Areas of low rainfall in India include places like western Uttar Pradesh, Delhi and Haryana. Apart from this, dry areas of eastern Rajasthan, Gujarat and Punjab also fall in this category. 

• The Deccan Plateau is also included in the low rainfall areas, where the problem of drought and water crisis is more common due to lack of rainfall.

4. Areas with very low rainfall (less than 50 cm)

• Areas with extremely low rainfall in India include Ladakh and western Rajasthan, which are known for their dry climate. Apart from this, parts of Andhra Pradesh, Karnataka and Maharashtra are also areas where rainfall is extremely low. 

• These areas are often drought-prone, adversely affecting agriculture and water resources.

6. Snowfall

• Snowfall is limited only to the Himalayan regions.

Monsoon and economic life of India

• Dependence on agriculture: 64% of India's population is dependent on agriculture, which is mainly based on the south-west monsoon.

• Year-round farming: It is warm all over India except the Himalayas, which makes farming possible throughout the year.

• Crop Diversity: Different characteristics of monsoon help in growing different types of crops.

• Drought and flood: Irregularity of rainfall causes drought or flood problems in some areas.

• Importance of Rainfall: Timely and adequate rainfall is good for farming but where there are no means of irrigation, less rainfall causes damage.

• Soil erosion: Heavy monsoon rains increase the problem of soil erosion.

• Beneficial for Rabi crops: Winter rains in North India are beneficial for Rabi crops.

• Impact on Lifestyle: India's climatic diversity also brings variations in food, clothing and houses.

global warming

Climate change is a natural process, but nowadays it is happening rapidly, and there are many reasons for this. Scientific evidence shows that earlier large parts of the Earth were covered with ice, and the changes that are happening now are related to human activities.

What is global warming?

Global warming means the increase in the temperature of the Earth. This is happening mainly due to the greenhouse effect. Some gases such as carbon dioxide (CO₂), methane, CFCs, and nitrous oxide are present in the atmosphere and trap solar energy and heat the Earth.

Human activities and global warming

The amount of these gases has increased due to industrialization and pollution, especially when we burn coal and petrol. This is increasing the temperature of the Earth. The temperature has increased in the last 150 years, and it is estimated that by 2100 it may increase by another 2° Celsius.

What will be the effect of increase in temperature?

• Sea level rise: Melting ice due to heat will raise sea levels, and they could rise by 48 centimetres by the end of the 21st century.

• Climate change: Some areas may become hotter and some drier, leading to changes in agriculture and ecosystems.

• Effect on health: Diseases like malaria can spread due to heat.

• Impact on India:  If the sea level rises by 50 cm, it will affect the coastal areas of India due to floods, climate change and agriculture. This can cause environmental crisis, which will have an impact on the whole world.