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THE CLIMATE OF INDIA


Published on: 12/15/2020 5:18:20 AM

India has a monsoon type of climate. The term “monsoon” is derived from Arabic word ‘mausim’ which means seasonal reversal in the wind direction. The climate of India influenced by the two types of winds – one blow from the Arabic Sea and second is from the Bay of Bengal.

FACTORS AFFECTING THE CLIMATE OF INDIA

  • Latitude: Tropic of Cancer separates the tropical and the sub-tropical areas. It further passes through the middle of Rann of Kuchchh in the west and Mizoram in the east. Therefore, the climate of India has characteristics of both tropical and sub-tropical climates.
  • The Himalayan Mountains: The lofty Himalayas in the north along with its extensions act as an effective climatic divide. The towering mountain chain provides an invincible shield to protect the subcontinent from the cold northern winds. These cold and chilly winds originate near the Arctic Circle and blow across central and eastern Asia.
  • Distribution of Land and Water: India is flanked by the Indian Ocean on three sides in the south and girdled by a high and continuous mountain-wall in the north.
  • Altitude: Temperature decreases with height. Due to thin air, places in the mountains are cooler than places on the plains. For example, Agra and Darjeeling are located on the same latitude, but temperature of January in Agra is 16°C whereas it is only 4°C in Darjeeling.
  • Relief: The physiography or relief of India also affects the temperature, air pressure, direction and speed of wind and the amount and distribution of rainfall.
  • Pressure and Winds: During winter, Himalayas have high pressure with the south having low pressure. The condition is just the opposite in summer.
  • Distance from sea: The land masses away from the sea experience continental climate and the ones nearby experience maritime climate. 
  • El Nino and La Nina: El Nino is a warm current which appears in the Peru coast in December. Warming of Pacific Ocean has a worldwide effect on the pressure and wind systems. La Nina is just the reverse, which brings the monsoon winds to India.
  • Southern Oscillation: The relationship between pressure difference in Pacific and Indian Ocean is called as the Southern Oscillation, in which high pressure over the Pacific Ocean results in low pressure over Indian Ocean.

FACTORS RELATED TO AIR PRESSURE AND WIND

We need to understand the mechanism of the following three factors to understand the differences in local climates of India:

  • Distribution of air pressure and winds on the surface of the earth.
  • Upper air circulation caused by factors controlling global weather and the inflow of different air masses and jet streams.
  • Inflow of western cyclones generally known as disturbances during the winter season and tropical depressions during the south-west monsoon period into India, creating weather conditions favourable to rainfall. The mechanism of these three factors can be understood with reference to winter and summer seasons of the year separately.

 

 

INTER TROPICAL CONVERGENCE ZONE (ITCZ)

The Inter Tropical Convergence Zone (ITCZ) is a low pressure zone located at the equator where trade winds converge, and so, it is a zone where air tends to ascend. In July, the ITCZ is located around 20°N-25°N latitudes (over the Gangetic plain), sometimes called the monsoon trough. This monsoon trough encourages the development of thermal low over north and northwest India. Due to the shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40° and 60°E longitudes and start blowing from southwest to northeast due to the Coriolis force. It becomes southwest monsoon. In winter, the ITCZ moves southward, and so the reversal of winds from northeast to south and southwest, takes place. They are called northeast monsoons.

 

SEASONS OF INDIA

The climate of India has distinct seasonal patterns. The weather conditions change greatly from one season to another. The changes in temperature are extreme in the interior regions. The coastal regions do not experience extreme temperatures.

Winter Season: This season is from the middle of December to February. During this period, the Sun rays fall perpendicular to the Earth in the southern hemisphere. So, India which is located in the northern hemisphere, receives less temperature. India receives rainfall especially in sub-Himalayan belt by Western disturbances.

Summer Season: This season is from March to the middle of June. The whole India experiences increase in temperature because of the summer solstice. During this season, hot violent winds blow during daytime in the north and northwest India which is famous as ‘loo’. Since the sun goes gradually towards the north (summer solstice), the Inter Tropical Convergence Zone (ITCZ) begins moving towards the north and passes the 250 latitude in July.

LOCAL WINDS IN INDIA

Local storms

Affected areas

Mango shower

South India (Useful for early ripening of mangoes)

Cherry Blossom shower

Karnataka and Kerala (Useful for blooming of coffee flowers)

Nor Westers or Kalbaisakhi

West Bengal, Assam, Odisha, Jharkhand

Loo

Northern Plains

Bardoli Chheerha (Bordochila)

Assam

Rainy Season: This season is from middle of June to September. During this time, a low air pressure belt is formed in the north-west India and Pakistan. The Inter Tropical Convergence Zone (ITCZ) moves towards the north and the reaches up to the foothills of Shiwaliks. A greater low pressure is formed on the Indian peninsula in comparison to that on the Arabian Sea because of it. The southeast trade winds blowing in the Southern Hemisphere turns towards the east after crossing the equator to fill this low pressure and the form of the southwest monsoon.

Autumn Season: This season comes after the rainy season which is start from the October to the middle of the December. This is season is popularly known as ‘the season of retreating monsoon’. During this season, several cyclonic storms develop in the Bay of Bengal, which move from the north-east to the south-west causing substantial amount of rainfall on the coast of Tamil Nadu and Sri Lanka.

CLIMATIC REGIONS OF INDIA

There are seven climatic regions of India which are discussed below:

1. Tropical Rain Forests Climate

Region: Western Ghats, West Coastal Plains, Andaman & Nicobar Island, Parts of Assam and Tripura

Features: High temperature throughout the year, heavy seasonal rainfall, annual rainfall which up to 200 cm

2. Tropical Savannah Climate

Region: Peninsular region except leeward side of Western Ghats

Features: Dry winters, annual rainfall varies from 76 cm to 150 cm

3. Tropical and Semi-Arid Steppes Climate

Region:  Central Maharashtra to Tamil Nadu especially rain-shadow belt

Features:

4. Tropical and Sub-tropical Steppes Climate

Region:  Punjab, Haryana and Kachchh region

Features: Temperature varies from 120-350 C

5. Tropical Desert Climate

Region: Western parts of Barmer, Jaisalmer and Bikaner districts of Rajasthan and parts of Kachchh

Features: Scanty rainfall (mostly in form of cloud burst), high temperature

6. Humid Sub-tropical Climate with dry winters

Region:  Southern Himalayas

Features: Mild winters and extremely hot summer

7. Mountain Climate

Region: Mountainous region (above 6000 m or more)

Features:  Rainfall varies from 62 cm to 254 cm during South-west Monsoon

DISTRIBUTION OF RAINFALL

The average rainfall in India is 125 cm and 75% of it, is caused by the southwest monsoon. Areas of heavy rainfall: Those areas of India where there is more than 200 cm rainfall. There are such main areas in India- (i) Western slopes of the Western Ghats; (ii) North-east India except Tripura and Manipur; (iii) Andaman & Nicobar Island.

Areas of scanty rainfall: Those areas of India where there is less than 50 cm rainfall. There are three such areas in India- (i) Northern Gujarat, Western Rajasthan and the southern parts of Punjab-Haryana; (ii) Rain-shadow area of the Western Ghats; (iii); Desert of Ladakh

BURSTING OF MONSOON

When low pressure is formed in the whole northern India in the beginning of June, there is rainfall with sudden thunderstorm and lightning in the form of southwest monsoon towards the Indian Ocean. It is known as the ‘bursting of monsoon’.

 

KOPPEN’S CLASSIFICATION OF CLIMATE

The Koppen climate classification divides climates into five main climate groups, with each group being divided based on seasonal precipitation and temperature patterns which are given below:

  • Tropical Moist Climates: all months have average temperatures above 18° Celsius
  • Dry Climates: with deficient precipitation during most of the year
  • Moist Mid-latitude Climates with Mild Winters
  • Moist Mid-Latitude Climates with Cold Winters
  • Polar Climates: with extremely cold winters and summers