Chapter - 4 Climate

 Chapter - 4 Climate

Weather:- Weather refers to the day-to-day condition of the atmosphere at a particular place and time. It includes elements like temperature, humidity, rainfall, wind speed, etc. Example: "It is raining today in Delhi."

Climate:- Climate is the average weather pattern of a place over a long period of time (usually 30 years or more). It describes general atmospheric conditions like overall temperature, rainfall, etc., of a region. Example: "India has a monsoon climate."

Climate of India

• India has a monsoon type climate.
• Influenced by latitude, altitude, and relief features.

3. Factors Affecting India’s Climate

Latitude

• The Tropic of Cancer (23.5°N) passes almost through the middle of India.
• It divides the country into two climate zones:
• Tropical zone (south of the Tropic): Hot throughout the year with less seasonal variation.
• Example: Chennai – remains warm even in winter.
• Subtropical zone (north of the Tropic): Has hot summers and cold winters.
• Example: Delhi – very hot in summer and cold in winter.

Altitude

• Temperature decreases as we go higher above sea level.
• Example: Shimla (in the hills) is cooler than Delhi, even though both are in the north.

• Pressure and Winds – Includes monsoon winds, jet streams, and western disturbances.
• Distance from the Sea – Coastal areas have moderate climate; interiors are extreme.
• Relief – Hills and mountains affect temperature and rainfall patterns.

Pressure and Winds:- Atmospheric pressure and winds play a major role in deciding the climate of India. The movement of air from high-pressure to low-pressure areas causes winds, which bring changes in temperature and rainfall.

Coriolis Force:-  The Coriolis Force is a force caused by the rotation of the Earth. It affects the direction of winds and ocean currents.

• It deflects moving air (winds) and water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
• Because India is in the Northern Hemisphere, winds here get deflected to the right.
• It carry moisture and bring rain.

During Winter:- There is a high-pressure area north of the Himalayas. Cold dry winds blow from this region to the low-pressure area over the oceans to the south.

Summer (Southwest Monsoon):- Low-pressure area develops over interior Asia, as well as, over northenwestern India. This cause a complete reversal of the direction of winds during summer. Air moves from the high-pressure area over the southern 

indian Ocean.

Indian Monsoon

• Monsoon: Seasonal reversal of winds bringing rainfall.
• Summer Monsoon (June–Sept): Moist winds from the sea to land → rainfall.
• Winter Monsoon (Oct–Feb): Dry winds from land to sea → less rain (except east coast).
• Retreating Monsoon (Oct–Nov): Withdrawal of monsoon; causes cyclones in Bay of Bengal.

Seasons in India

1. Cold Weather Season (Dec–Feb):- This season is known as winter in India. It lasts from December to February.
Key Features:

• Cool Temperatures:
• The northern plains become very cold, especially in January.
• Example: Delhi, Amritsar, and Srinagar experience low temperatures.
• The southern parts of India (like Chennai and Kochi) remain warm.
• Clear Skies and Dry Weather:
• The weather is mostly clear with little rainfall in most areas.
• Humidity is low.
• Western Disturbances:
• These are winds that come from the Mediterranean Sea.
• They bring light rain to north and northwest India, especially Punjab and Haryana.
• Mahawat:- Winter rainfall locally known as "Mahawat".
• This rain is important for the rabi crops like wheat.
• High Pressure Over Land:
• A high-pressure area forms over north India.
• Winds blow from the land to the sea, which makes the season dry.

2. Hot Weather Season (Mar–May):- 

High Temperatures:

• Temperatures rise steadily throughout the country.
• Example: Northern plains like Delhi, Jaipur, and Lucknow often see temperatures above 40°C in May.
• Central India becomes extremely hot, especially in areas like Nagpur.

Low Pressure Over North India:

• Due to the intense heat, a low-pressure area develops over northwestern India.
• This low pressure attracts moist winds from the sea, which later helps bring the monsoon.

Hot and Dry Winds – "Loo":

• In northern India, hot, dry winds called Loo blow in the afternoons during May and June.
• These winds can cause heatstroke and are dangerous.

Local Thunderstorms:

• In eastern India, especially in West Bengal and Assam, strong winds with rain and thunderstorms occur.
• These storms are called "Kalbaisakhi" or Nor’westers.
• They help cool down the region and are useful for early crops.

Dust Storms:- In northwestern India, occasional dust storms occur, which may bring light rain.

3. Advancing Monsoon (Rainy Season – June to September):- This season is also called the monsoon season and is the main rainy season in India.

Key Features:

Arrival of the Monsoon:

• The Southwest Monsoon winds begin to blow from the sea toward the land.
• These winds carry a lot of moisture from the Arabian Sea and Bay of Bengal.
• First hits Kerala around June 1, then spreads across the country.

Heavy Rainfall:

• These winds bring heavy rainfall to most parts of India.
• Western Ghats, Northeast India, and coastal areas receive very high rainfall.
• Example: Mawsynram in Meghalaya gets the highest rainfall in the world.

Two Branches of Monsoon:

• Arabian Sea Branch: Hits the Western Ghats, giving heavy rain to Kerala, Karnataka, Maharashtra.
• Bay of Bengal Branch: Moves towards northeast India, then towards the north and northwest.

Breaks in Monsoon:- Rain does not fall continuously; it comes in intervals. These gaps are called "breaks in monsoon."

Effect on Agriculture:-  Monsoon rains are very important for farming in India. Farmers depend on this season to grow rice, cotton, sugarcane, etc.

Retreating Monsoon / Transition Season (October–November):- This season marks the withdrawal of the monsoon from India and is also called the post-monsoon or transition period.

Key Features:

Withdrawal of Monsoon:

• The Southwest Monsoon starts retreating from northwestern India by early October.
• It gradually moves out of the country by mid-November.

Clear Skies and Rising Temperatures (October Heat):

• After the rain stops, skies become clear.
• The temperature remains high during the day, especially in southern India.
• This hot and humid weather in October is called “October Heat.”

Shift in Pressure and Wind Pattern:

• The low-pressure area shifts to the Bay of Bengal.
• Winds change direction and start blowing from land to sea.

Rainfall in Tamil Nadu and Coastal Andhra Pradesh:

• The Northeast Monsoon winds pick up moisture from the Bay of Bengal.
• These bring rainfall to Tamil Nadu, southern Andhra Pradesh, and parts of Kerala.

Cyclones:

• This season is also known for cyclonic storms in the Bay of Bengal.
• These can cause heavy damage, especially along the eastern coast.

Distribution of Rainfall:- Rainfall in India is unevenly distributed. Some areas receive very heavy rainfall, while others get very little.

1. Areas of High Rainfall (More than 200 cm per year):- Found in the Western Ghats, Northeast India, and Himalayan foothills. Example: 

• Mawsynram (Meghalaya) – highest rainfall in the world.
• Western coast – Kerala, Karnataka, and Goa.
• Assam and Arunachal Pradesh.

2. Areas of Moderate Rainfall (100–200 cm per year):
Found in most of the northern plains, eastern Rajasthan, Madhya Pradesh, and parts of the Deccan Plateau. Examples:- West Bengal, Uttar Pradesh, Maharashtra (some parts).
3. Areas of Low Rainfall (50–100 cm per year):- Includes interior Deccan, central Rajasthan, Punjab, and Haryana. Rainfall is less but still enough for some crops.
4. Areas of Very Low Rainfall (Below 50 cm per year):- Found in desert and semi-desert areas.  Examples:- Western Rajasthan (like Jaisalmer), Parts of Ladakh.

Monsoon as a Unifying Bond:- Although India has diverse geography, cultures, and languages, the monsoon acts as a unifying force that brings the whole country together.

Temeperature in Different region

• Himalayas protect the subcontinent from extermely cold winds from central asia. Northen India to have uniformly higher temperatures compared to other areas on same latitudes.
• Peninsular Plateau:- Under the influence of the sea from three sides, has moderate temeperatures. 

Monsoon:- Most parts of India wait eagerly for the monsoon rains, especially after the hot summer.

• The arrival of monsoon is celebrated across regions in different ways, showing its emotional and cultural importance.
• A large part of India’s population depends on farming, and most crops need monsoon rain.
• Example: Crops like rice, sugarcane, and cotton are mainly grown with monsoon water.
• So, farmers across India share the same hope and concern for good rainfall.