Revision: Geography >> Climate and Natural Vegetation of India Social Science SSLC (English Medium) Class 10 Tamil Nadu Board of Secondary Education

Definitions [1]

Season: A season is a period of the year that is distinguished by special climate conditions.

Key Points

Key Points: Climate of India

India lies between 8°4′N and 37°6′N, giving it both tropical and temperate climates.
It has a tropical monsoon climate with high temperatures and seasonal rainfall.
The Tropic of Cancer divides India into southern tropical and northern temperate zones.
The Himalayas block cold winds, and the Indian Ocean provides moisture for monsoon rains.
In summer, south-west monsoon winds bring heavy rain to coastal and mountain areas.
North-east monsoon winds bring some rain to the south during the retreating monsoon.
India's diverse geography causes regional climate differences and natural disasters like floods, droughts, and cyclones.

Key Points: Factors Affecting India's Climate

Latitude – Southern India is warmer as it lies in the tropical zone; northern India lies in the temperate zone.
Altitude – Temperature decreases with height; hills are cooler than plains.
Distance from Sea – Coastal areas have moderate climate; interior areas have extreme climate.
Himalayas – Block cold winds and cause rainfall by stopping monsoon winds.
Monsoon & El Niño – Monsoon controls rainfall; El Niño weakens monsoon, La Niña strengthens it.

Key Points: Seasons in India > Hot Dry Summer

Hot dry summer season lasts from March to May due to the sun’s vertical rays moving towards the Tropic of Cancer.
High temperatures occur in interior India, while coastal and hilly areas are cooler.
Low pressure develops over north and northwest India; seas have high pressure.
Local winds like Loo and Kalbaisakhi blow during this season.
Pre-monsoon showers (Mango/Blossom showers) help crops like tea, coffee, rice, and mango.

Key Points: Seasons in India > The South-West Monsoon Season

South-West Monsoon season lasts from June to September and is the main rainy season of India.
It is caused by differential heating of land and sea, creating low pressure over north-west India and high pressure over surrounding seas.
South-East Trade Winds, after crossing the Equator, are deflected by the Coriolis force and blow as South-West Monsoon winds.
These winds divide into two branches due to India’s peninsular shape: Arabian Sea branch and Bay of Bengal branch.
The monsoon brings heavy, uneven rainfall, with orographic rain on windward slopes, while Tamil Nadu and western Rajasthan receive little rainfall.

Key Points: Seasons in India > Retreating Monsoon

Retreating Monsoon season occurs during October and November due to the weakening of the low-pressure trough over the Ganga plains.
The retreat of monsoon is caused by the southward movement of the sun, leading to high pressure replacing low pressure over northern India.
Clear skies, high humidity, and high temperature cause uncomfortable weather called ‘October Heat’.
Cyclonic depressions form over the Bay of Bengal and Andaman Sea, bringing heavy rainfall to Tamil Nadu, Odisha, and coastal Karnataka.
Interior Deccan remains dry due to the rain-shadow effect of the Eastern Ghats, while the Coromandel Coast receives most of its rainfall.

Key Points: Distribution of Rainfall

Distribution of rainfall in India depends on pressure conditions, relief features, wind direction, and cyclonic depressions.
Heavy rainfall regions (more than 200 cm) include the windward slopes of the Western Ghats and the Meghalaya–Assam hills.
Moderate rainfall regions (100–200 cm) include the Middle Ganga Valley, parts of Odisha, Madhya Pradesh, Maharashtra, Andhra Pradesh, and Tamil Nadu.
Low rainfall regions (50–100 cm) include parts of the Deccan Plateau, Punjab, Haryana, eastern Rajasthan, and Kashmir.
Scanty rainfall regions (less than 50 cm) include the Thar Desert, Kachchh, and rain-shadow areas of the Deccan Plateau, making rainfall in India uneven and uncertain.

Key Points: Introduction of Natural Vegetation

Natural vegetation refers to plants that grow naturally without human help and remain undisturbed for a long time.
It includes trees, shrubs, grasses, climbers, and creepers that adjust to the climate and soil of the region.
Climate factors like temperature and rainfall determine the type of natural vegetation in an area.
The Tropic of Cancer divides India into tropical (south) and temperate (north) regions, affecting vegetation patterns.
Flora means plant species of a region, vegetation means plant communities, and a forest is a large area covered with trees and undergrowth.

Key Points: Major Types of Vegetation in India

India has diverse natural vegetation due to variations in climate, soil, and relief.
The Western Ghats and Andaman–Nicobar Islands have tropical evergreen forests.
Tropical deciduous (monsoon) forests are found in regions with seasonal rainfall.
Desert and semi-desert regions of Rajasthan have thorny and scrub vegetation.
India’s vegetation is broadly divided into five types: Tropical Evergreen, Tropical Deciduous, Tropical Desert, Littoral (Mangroves), and Mountain forests.

Key Points: Tropical Evergreen or Rain Forests

Tropical Evergreen (Rain) Forests are found in areas with more than 200 cm rainfall, high temperature (25°C–27°C) and high humidity.
They are mainly found on the western slopes of the Western Ghats, North-Eastern India, and the Andaman & Nicobar Islands.
These forests are dense and multi-layered, with very tall trees (over 60 m) and little sunlight reaching the forest floor.
Trees do not shed leaves at the same time, so the forests remain green throughout the year and have rich biodiversity.
Important trees include rosewood, ebony, mahogany, sissoo and gurjan, which provide hard and durable timber, though forests are not fully exploited due to dense growth.

Key Points: Tropical Deciduous Forest

Tropical Deciduous (Monsoon) Forests are the most widespread forests in India and occur in areas with 100–200 cm rainfall.
These forests are of two types: Moist Deciduous (100–200 cm rainfall) and Dry Deciduous (70–100 cm rainfall).
Trees shed their leaves for 6–8 weeks during summer to reduce water loss and survive dry conditions.
They are found along the foothills of the Himalayas, eastern slopes of the Western Ghats, Peninsular Plateau, and parts of Uttar Pradesh, Bihar, Maharashtra, and Karnataka.
Important trees include teak, sal, sandalwood, shisham, mahua, and tendu, and these forests are commercially the most exploited in India.

Key Points: Mountain or Montane Forest

Mountain (Montane) Forests occur at 1000–4000 m altitude, where temperature decreases with height.
These forests are found mainly in the Himalayas and also in Vindhyas, Nilgiris, Western and Eastern Ghats.
Vegetation changes with altitude—deciduous forests at foothills, conifers (pine, deodar, spruce) at higher levels, and alpine grasslands near the snowline.
Climatic conditions include 12°C–13°C temperature, 100–300 cm rainfall, and moderate humidity.
In Peninsular India, temperate mountain forests are called Sholas, found in Nilgiris, Anaimalai and Palani hills.

Key Points: Mangrove Forests (Tidal Forest)

Littoral or Tidal (Mangrove) Forests grow in wet, marshy, coastal and delta regions where land meets sea.
These forests occur in areas with 26°C–29°C temperature and rainfall below 200 cm.
They are mainly found in the Sundarbans (Ganga Delta), Andaman & Nicobar Islands, and the Mahanadi, Godavari, and Krishna deltas.
Trees have special adaptations like stilt roots and breathing roots (pneumatophores) to survive in waterlogged and saline conditions.
Important trees include sundari, rhizophora, keora, palms, and canes, which provide fuel and durable timber.

Key Points: Indian Wildlife

India is a mega-diverse country with animals like elephants, rhinos, camels, wild ass, snow leopards, and yaks found in different habitats.
Tigers and lions are both found in India, making it unique in the world.
Aquatic animals like turtles, crocodiles, gharials, and Gangetic dolphins live in rivers, estuaries, and coastal areas.
Birds like peacocks, Indian bustards, kingfishers, cranes, and others are found in forests and wetlands.
Wildlife is threatened by poaching, pollution, and deforestation, so India has established national parks and sanctuaries to protect it.

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