Climate of India Notes

Climate of India

• Also referred to as the Indian Subcontinent.
• Lacks uniform climatic conditions with great differences in rainfall (RF) and temperature.
• Monsoon unifies the climate.
• India is considered a ‘Geographical Laboratory’.

General Climate

• Most of India experiences a tropical climate.
• Vast area influenced by the monsoon (seasonal reversal of wind pattern).
• The climate is described as ‘TROPICAL MONSOON CLIMATE’.

Factors Affecting Climate

• Location
• Distance from the sea
• Relief
• Monsoon winds
• Upper air currents/jet streams

Location

• The Tropic of Cancer divides India into two halves.
  • Northern India: Temperate
  • Southern India: Tropical

Distance from Sea

• North of Tropic of Cancer (interior): Extreme climate.
• South of Tropic of Cancer (coastal): Equable climate.

Relief

• Himalayas prevent cold winds from the north.
• They block monsoon winds, causing rainfall.
• Western Ghats cause heavy rainfall on the windward side.

Monsoon

• Derived from the Arabic word Mausim, meaning seasonal reversal of wind pattern.

Climatic Seasons (IMD)

• Hot dry season (March – May)
• Rainy season/Southwest monsoon season (June to mid-September)
• Retreating monsoon season (Mid-September – November)
• Cold weather season/Winter season (Early Dec to end of Feb)

Hot Dry Season (Summer)

• Weather is hot, dry.
• Temperature increases towards north.
• Low pressure prevails.
• Maximum temperature in May in Thar (up to 48^0).
• Highest recorded temperature: 49.4^0 @ Ganganagar (Rajasthan).
• Coastal areas have modified temperatures due to the sea.
• High mountains have low temperatures.
• Convectional rain occurs in some regions.
• Thunderstorms with strong winds occur occasionally (Kalbaisakhi in W.B, Andhis in U.P, coffee blossom in Karnataka, Mango shower in Kerala).
• Loo (hot dusty wind) are common in the northern plain.

Characteristic Features

• Dry weather.
• High temperature in tropical India.
• High temperature range in interior parts and low in coastal areas.
• Thunderstorms and dusty winds are common.
• Brief showers occur.

Southwest Monsoon Season (Rainy Season)

• June to mid-September.
• Moist wind blows from SW towards land due to low pressure over the landmass.
• Winds are known as SW Monsoon.
• Gives rainfall to most regions.
• Branches:
  • Arabian Sea Branch (65% contribution)
  • Bay of Bengal Branch (35% contribution)

Arabian Sea Branch

• Blows from SW, obstructed by Western Ghats.
• Descending on eastern slopes makes it dry, giving less rainfall (rain shadow region).
• Part obstructed by Vindhyas, Satpuras, and Central Mountains.
• Rainfall decreases from W to E.
• Rainfall is Orographic in nature.

Bay of Bengal Branch

• Gains moisture over the Bay of Bengal.
• Strikes hills of Meghalaya and Assam, causing heavy rainfall.
  • Highest: Mawsynram (1147 cm).
  • Cherrapunji (1081cm).
• Turns towards W and blows across N. India.
• Rainfall decreases towards W, giving little rainfall to Thar.
• Andaman and Nicobar Islands receive first rainfall from this branch.

Retreating Monsoon Season

• Mid-September to November.
• Also known as N.E Monsoon.
• Period of unsettled weather.

Causes of Occurrence

• Due to the sun’s apparent movement, L.P develops over the surrounding water body and H.P over the landmass.
• Southwest monsoon changes direction to NE winds.
• Winds pick up moisture from the Bay of Bengal while retreating.
• Due to the Coriolis force, winds are deflected towards the right.
• Reaches the Coromandel coast giving moderate rainfall to the coast of T.N & A.P.
• Other parts do not receive rainfall.
• Tropical cyclones are common and frequent causing heavy rainfall and damage along their path.

Winter Season

• Early Dec to end of Feb.

Characteristics

• Low temperature.
• Clear sky.
• Low humidity.
• Light northerly wind prevails.
• Temperature increases from N to S.
• Cool in the north and warm in the south.
• January is the coldest month.
• Hill areas of J&K and Himachal Pradesh record lowest temperatures.
• Dras valley in Kashmir near Kargil has the lowest temperature.
• High pressure in the interior part.
• Little rainfall from the depression of the Mediterranean region.

Mechanism of Monsoon

• Still not clearly known.

Earlier View

• High temperature and Low Pressure in central Asia in summer.
• Surrounding ocean had low temperature and High Pressure.
• Wind moved from sea to land during summer.
• Vice versa in winter.

Modern Theory

Air Mass Theory

• N.E trade winds and S.E trade winds meet at the equator.
• This region is called ITCZ (Inter Tropical Convergence Zone).
• ITCZ shifts N of Equator in summer and S of Equator in winter.
• While shifting N, S.E trade wind from Sn hemisphere crosses the equator and blows as S.W and gives rainfall. This is known as S.W Monsoon.

Jet Stream Theory

• Jet stream – Band of fast-moving air found in mid-latitudes in the upper troposphere.

• Westerly jet stream is located along Sn slope of Himalayas in winter; suddenly shifts N and flows over the Tibetan plateau.

• This periodic movement of sub-tropical jet stream indicates the arrival and withdrawal of the monsoon.

• Recent observations reveal the interconnection between the intensity and duration of heating of the Tibetan plateau and monsoon rain in India.

• Higher the intensity and duration, the more the rainfall and vice versa.

Annual Distribution of Rainfall

• Uneven, uncertain, irregular.
• Great variation in the amount of rainfall in various parts.

Factors Determining Distribution

• Direction of moist laden wind.
• The relief features.
• Passage of cyclone.

Rainfall Regions

• Areas of very high rainfall (>200 cm): Southern slopes of En Himalayas, Assam hill regions, Wn slope of the Wn Ghats.
• Areas with high rainfall (100-200 cm): Middle Ganga valley, Nn part of Andra Pradesh and Sn part of Tamil Nadu, Parts of Wn Ghats and En Maharastra.
• Areas with Low Rainfall (50-100 cm): Upper Ganga valley, En Rajasthan, Sn Deccan comprising plateau region of Karnataka, parts of Andhra Pradesh and Tamil Nadu.
• Areas with very low Rainfall (<50 cm): Wn Rajasthan, Sn Punjab, Nn most part of Kashmir, rain shadow regions of Wn Ghats.