Climate ||Geography|| Chapter 4 NCERT Notes
1. Climate vs Weather
- Climate: Refers to the average weather conditions of a large area over a long period (30 years or more).
- Weather: The day-to-day state of the atmosphere at a place, including temperature, humidity, rainfall, etc.
2. Climatic Conditions in India
- India’s climate is primarily monsoonal.
- The country experiences variations in temperature and rainfall across different regions and seasons.
- India has four main seasons: Summer, Winter, Monsoon, and Post-Monsoon (Autumn).
3. Factors Affecting India’s Climate
Several factors influence India's climate:
a) Latitude
- India lies between 8°4’ N and 37°6’ N latitudes.
- The Tropic of Cancer (23°30'N) passes through the middle of the country.
- Areas to the south of the Tropic of Cancer experience a tropical climate, while areas to the north have a subtropical climate.
b) Altitude
- The Himalayas in the north prevent the cold winds from Central Asia from entering India.
- The high altitude of the Himalayas influences temperatures, keeping the northern plains relatively warmer during winters.
- Coastal regions have moderate climates due to their proximity to the sea, while the interior parts have more extreme climates.
c) Pressure and Winds
- India’s climate is influenced by various pressure belts and wind systems:
- Pressure Systems:
- During winters, a high-pressure system develops in northern India, leading to cold and dry winds.
- In summers, low-pressure systems dominate, pulling in moist winds from the sea.
- Winds:
- Trade Winds: Prevailing winds that blow from the northeast in the northern hemisphere.
- Monsoon Winds: These are seasonal winds that reverse their direction in different seasons. India receives most of its rainfall from the Southwest Monsoon.
- Pressure Systems:
4. The Indian Monsoon
The Indian monsoon is the most significant feature of the country's climate. Monsoon winds are seasonal winds that bring rainfall and have two main branches:
Southwest Monsoon (Summer Monsoon):
- During summers (June-September), the low-pressure system over north India draws in moisture-laden winds from the Indian Ocean.
- These winds bring heavy rainfall to most parts of India.
- Arabian Sea Branch: Causes rainfall in the western coastal regions and later moves towards northern India.
- Bay of Bengal Branch: Moves towards the northeastern states and the northern plains.
Northeast Monsoon (Winter Monsoon):
- During winters (October-February), high-pressure conditions over northern India cause winds to blow from the land to the sea.
- These winds are dry and bring little to no rainfall, except for some parts of the southeast coast (Tamil Nadu) due to the retreating monsoon.
5. Climatic Seasons in India
a) Cold Weather Season (Winter)
- Duration: December to February.
- Temperature: Temperatures are low, especially in the northern parts of India.
- Features:
- The northern plains experience cold winds.
- Coastal regions remain warmer due to the influence of the sea.
- Some places in northwestern India experience frost, and snowfall occurs in the Himalayan regions.
b) Hot Weather Season (Summer)
- Duration: March to May.
- Temperature: High temperatures, especially in northern and central India.
- Features:
- Loo: Hot, dry winds blow over the northern plains.
- Coastal regions remain relatively cool due to sea breezes.
- Thunderstorms and pre-monsoon showers, known as Kalbaisakhi in West Bengal, and Mango showers in Kerala, provide some relief.
c) Advancing Monsoon (Rainy Season)
- Duration: June to September.
- Temperature: High, with heavy rainfall across the country.
- Features:
- Caused by the Southwest Monsoon winds.
- Western Ghats receive heavy rainfall, while places in the interior Deccan Plateau get less rainfall due to the rain-shadow effect.
- North India and the eastern regions receive significant rainfall, supporting agriculture.
d) Retreating Monsoon (Post-Monsoon Season)
- Duration: October to November.
- Temperature: Starts cooling down.
- Features:
- The Northeast Monsoon winds bring rain to the southeastern coast, particularly Tamil Nadu.
- Cyclones in the Bay of Bengal may affect the eastern coast during this season.
6. Distribution of Rainfall in India
Regions of High Rainfall:
- Areas like Meghalaya (Cherrapunji and Mawsynram) receive the highest rainfall in the world.
- The Western Ghats, northeastern states, and the Himalayan foothills also receive high rainfall.
Regions of Moderate Rainfall:
- Most of the northern plains and coastal regions receive moderate rainfall (100-200 cm annually).
Regions of Low Rainfall:
- The Thar Desert in Rajasthan receives very low rainfall (less than 50 cm annually).
- The Deccan Plateau and parts of Gujarat also receive relatively low rainfall.
7. Impact of Monsoon on Agriculture
- Agriculture in India is heavily dependent on the monsoon, as the majority of the country’s crops are grown during the rainy season.
- A delayed or weak monsoon can cause droughts, affecting crop yields and leading to food shortages.
- Conversely, excessive rainfall can cause floods, damaging crops and infrastructure.
8. Monsoon Variability and Climate Change
- The monsoon is not uniform; it varies in terms of onset and duration.
- Climate change is affecting the monsoon patterns, leading to unpredictable rainfall, causing droughts and floods in different regions.
Summary of Key Points:
- India’s climate is primarily monsoonal, characterized by seasonal reversal of winds.
- Factors like latitude, altitude, pressure systems, and winds influence the climate.
- The Southwest Monsoon brings most of the rainfall, while the Northeast Monsoon affects parts of southern India.
- India experiences four seasons: Winter, Summer, Rainy, and Post-Monsoon.
- Rainfall distribution varies, with the northeastern states and the Western Ghats receiving the most rain, and deserts receiving the least.
- The monsoon plays a critical role in agriculture but is also vulnerable to variability due to climate change.