CLIMATE OF INDIA
Geography
BASIC CONCEPTS
• Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than 30 years).
• Weather refers to the state of the atmosphere over an area at any point of time.
• Elements of weather and climate:
- Temperature
- Atmospheric pressure
- Wind
- Humidity
- Precipitation
========================================================
FACTORS DETERMINING THE CLIMATE OF INDIA
========================================================
These factors are grouped into two categories:
1. Factors related to Location and Relief
2. Factors related to Air Pressure and Winds
----------------------------------------
A) FACTORS RELATED TO LOCATION AND RELIEF
----------------------------------------
1. Latitude:
• Southern part of India (south of Tropic of Cancer) lies in tropical zone.
• Northern part lies in subtropical and temperate zone.
• Tropical areas have:
- High temperature throughout the year
- Low annual range of temperature
• Northern India experiences:
- Extreme climate
- High daily and annual temperature range
2. The Himalayan Mountains:
• Act as a climatic barrier.
• Protect India from cold continental winds of Central Asia.
• Force monsoon winds to shed moisture inside the subcontinent.
3. Distribution of Land and Water:
• Land heats and cools faster than water.
• This creates seasonal pressure differences.
• These pressure differences cause reversal of monsoon winds.
4. Distance from the Sea:
• Coastal areas have equable climate.
• Interior areas experience extreme climate.
5. Altitude:
• Temperature decreases with height.
• Example:
- Agra and Darjeeling are on same latitude.
- January temperature: Agra ≈ 16°C, Darjeeling ≈ 4°C.
6. Relief:
• Relief affects:
- Direction and speed of winds
- Rainfall distribution
• Example:
- Windward side of Western Ghats and Assam get heavy rainfall.
- Leeward plateau remains dry.
----------------------------------------
B) FACTORS RELATED TO AIR PRESSURE AND WINDS
----------------------------------------
• Distribution of air pressure and winds
• Upper air circulation and jet streams
• Western disturbances and tropical cyclones
========================================================
MECHANISM OF WEATHER IN WINTER SEASON
========================================================
1. Surface Pressure and Winds:
• High pressure over north of Himalayas.
• Cold dry winds blow from Central Asia to India.
• These are dry continental winds.
• Sometimes they influence up to middle Ganga plain.
2. Jet Stream and Upper Air Circulation:
• Westerly jet streams blow at 9–13 km height.
• Tibetan plateau acts as barrier.
• Jet stream splits into two branches:
- Northern branch north of Tibet
- Southern branch south of Himalayas
• Southern branch (around 25°N) affects Indian winter weather.
3. Western Disturbances and Tropical Cyclones:
• Western disturbances originate over Mediterranean Sea.
• Bring winter rainfall to northwest India.
• Tropical cyclones originate in Bay of Bengal and Indian Ocean.
• Affect Tamil Nadu, Andhra Pradesh and Odisha coasts.
========================================================
INTER TROPICAL CONVERGENCE ZONE (ITCZ)
========================================================
• Low pressure zone near equator where trade winds meet.
• In July, ITCZ shifts to around 20°N – called Monsoon Trough.
• Causes development of thermal low in north-west India.
• Southeast trade winds cross equator and become Southwest Monsoon.
• In winter, ITCZ shifts south – causing Northeast Monsoon.
========================================================
MECHANISM OF WEATHER IN SUMMER SEASON
========================================================
1. Surface Pressure and Winds:
• ITCZ shifts north between 20°N and 25°N.
• Westerly jet withdraws.
• Moist maritime tropical air from southern hemisphere flows towards India.
• This becomes Southwest Monsoon.
2. Jet Streams and Upper Air Circulation:
• Easterly jet stream flows over southern peninsula in summer.
• Helps in steering tropical depressions into India.
========================================================
NATURE OF INDIAN MONSOON
========================================================
Important aspects:
• Onset of monsoon
• Rain-bearing systems
• Break in monsoon
----------------------------------------
ONSET OF MONSOON – CAUSES
----------------------------------------
• Differential heating of land and sea
• Northward shift of ITCZ
• Withdrawal of westerly jet
• Establishment of easterly jet at 15°N
• Easterly jet is responsible for monsoon burst
----------------------------------------
RAIN BEARING SYSTEMS
----------------------------------------
• Bay of Bengal branch
• Arabian Sea branch
----------------------------------------
EL-NINO AND INDIAN MONSOON
----------------------------------------
• El-Nino appears once in 3–7 years.
• Warm current replaces cold Peruvian current.
• Causes:
- Distortion of atmospheric circulation
- Irregular rainfall
• Used for long-range monsoon forecasting.
• Strong El-Nino generally weakens Indian monsoon.
----------------------------------------
BREAK IN THE MONSOON
----------------------------------------
• Temporary dry spells during rainy season.
• Caused by:
- Shifting of monsoon trough
- Weak rain-bearing systems
========================================================
LOCAL STORMS OF HOT WEATHER SEASON
========================================================
• Mango Showers – Kerala and Karnataka (help mango ripening)
• Blossom Showers – help coffee flowers
• Nor-Westers (Kalbaisakhi / Bordoisila) – Bengal and Assam
• Loo – hot, dry winds in northern plains
========================================================
SOUTH-WEST MONSOON SEASON
========================================================
• Word monsoon comes from Arabic word “Mausim” meaning season.
• Causes:
- Differential heating
- ITCZ shift
- Jet streams
- El-Nino / La-Nina
PROCESS OF FORMATION:
• Strong low pressure develops over NW India in May.
• Southeast trade winds cross equator.
• They become southwest monsoon winds.
• Sudden arrival is called “burst of monsoon”.
----------------------------------------
TWO BRANCHES OF MONSOON
----------------------------------------
1. Arabian Sea Branch
• Hits Western Ghats – heavy rainfall (250–400 cm).
• Creates rain shadow region east of Ghats.
• One branch goes through Narmada–Tapi valley.
• One branch goes to Rajasthan and Punjab.
2. Bay of Bengal Branch
• Deflected by Arakan Hills.
• Splits into:
- Ganga plain branch
- Brahmaputra valley branch
• Mawsynram receives highest rainfall in the world.
----------------------------------------
CHARACTERISTICS OF MONSOONAL RAINFALL
----------------------------------------
• Seasonal (June–September)
• Controlled by relief
• Uneven distribution
• Occurs in wet spells and breaks
• Heavy downpours cause erosion
========================================================
RETREATING MONSOON (OCTOBER–NOVEMBER)
========================================================
• Monsoon trough shifts southward.
• Clear skies and rise in temperature – called October Heat.
• Cyclonic depressions cause rain in Tamil Nadu coast.
• Godavari, Krishna and Kaveri deltas are frequently affected.
========================================================
DISTRIBUTION OF RAINFALL IN INDIA
========================================================
• Average annual rainfall: about 125 cm
1. High Rainfall Areas (>200 cm):
• Western Ghats
• Sub-Himalayan region
• Meghalaya plateau
2. Medium Rainfall Areas (100–200 cm):
• Eastern MP, Odisha, Jharkhand, Bihar
• Eastern Tamil Nadu, Cachar valley
3. Low Rainfall Areas (50–100 cm):
• Western UP, Delhi, Haryana, Punjab, Gujarat, Deccan plateau
4. Inadequate Rainfall (<50 cm):
• Western Rajasthan
• Ladakh
• Parts of Karnataka, Maharashtra, Andhra Pradesh
• Snowfall is confined to Himalayan region.
========================================================
CONCLUSION
• Indian climate is monsoon type.
• It is controlled by:
- Latitude
- Relief
- Pressure systems
- Wind circulation
• Monsoon is the backbone of Indian agriculture and economy.
PDF File:
No PDF attached
Subject: Geography
← Back