Rajasthan Board RBSE Class 9 Social Science Notes Chapter 14 Climate of India
Climate:
- The word ‘Monsoon’ is derived from the Arabic word ‘Mawsim’ which means seasonal winds or seasons. Due to the effect of monsoon winds, the climate of India is known as monsoon winds.
- India’s climate is controlled by various factors, i.e., monsoon winds, altitude (height from sea- level), distance of sea, latitude (distance from equator), location of mountains and excessive atmospheric pressure.
Origin and Development of Monsoon:
- We have two views regarding this – traditional view and latest view.
- Traditional view is associated with Dr. Koteshwarao’s research. This view is related with the parallel rays of the sun along the Tropic of Cancer and Tropic of Capricorn. When the sun rays fall direct on the Tropic of Cancer, area around Multan becomes very hot and low pressure is formed. Contrary to it high-pressure area is formed over the Indian Ocean and Australia. High pressure winds, full of moisture (South-Western winds) move towards low pressure area, are obstructed by the Himalayas and the rains are caused in India. It is known as South-West Monsoon or Summer Monsoon.
- Latest view is associated with Ramaswami, Rammurti and Jambunath, Anantkrishnan, Flon, etc. It is related with the development of periodical storms in Troposphere. Phenomenon of rainfall is explained in terms of jet streams – tropical eastern jet and semi-tropical western jet.
- With the reversal of direction of winds due to sun rays parallel to the Tropic of Capricorn, high pressure is formed around Multan and low pressure in the area around sea. Winds (dry winds) blow from land towards sea, known as Winter Dry Winds or Winter Monsoons.
Classification of Climatic Conditions:
- Pre-Monsoon Conditions: Extreme hot, storm, flow of winds from sea towards land.
- Advancing Monsoon Conditions: Rains in India from south-western winds originating from Bay of Bengal and the Arabian Sea.
- Retreating Monsoon Conditions: Monsoon winds start retreating, temperature starts falling and high pressure belt starts developing.
Seasons are classified in two types in India according to the Meteorological Department:
- North-East or Winter Monsoon Period:
- Winter Season: December to February
- Summer Season: March to mid-June
- Monsoon or Summer Monsoon Period:
- Rainy Season: Mid-June to mid-September
- Autumn Season: Mid-September to mid-December
Classification of Seasons according to the Indian Culture
- Spring Season: Chaitra to Baisakh (March to April)
- Summer Season: Jaishth to Aashadh (May to June)
- Rainy Season: Sahravan to Bhadrapad (July to August)
- Autumn Season: Aashwin to Kartik (September to October)
- Winter Season: Margshirsh to Paush (November to December)
- Cold Season: Magh to Phalgun (January to February)
North- East or Winter Monsoon Period
Winter Season:
- Temperature: In the North-lndia, temperature remains low and the winters are severe because of distance from equator and ocean as well as height above the sea-level. Temperature in the southern India remains high because of nearness to Equator and maritime influence. In the winters temperature in the Northern India falls, sometimes, below freezing point. Usually, the average temperature is, usually, less than 21°C but it is more in the south.
- Air Pressure and Winds: High pressure areas are formed over the central Asia and low pressure over the Indian Ocean area. Hence, winds blow from the high-pressure area of the Central Asia to the Oceanic low pressure area. Winds blowing towards the Sea, along with Mediterranean cyclones cause rainfall, which are called ‘Mavath’.
- Rainfall: The North-Western part of India receives rainfall from cyclones of the Mediterranean sea and the Southern part from the retreating monsoons. Jammu-Kashmir, Punjab, Haryana, Rajasthan, Uttarakhand and Uttar Pradesh receive rainfall from the Mediterranean sea cyclones whereas Tamil Nadu in south receives rainfall from the retreating monsoons.
Summer Season:
- Temperature: There is immense heat and appreciable rise in temperature from March to mid-June, in the Northern India due to parallel rays of the sun in the Northern Hemisphere, distance from sea and anti-cyclonic effect. Very often temperature touches 50°C in the Northern India. In the Southern India, temperature is relatively low because of the influence of sea.
- Air Pressure and Winds: Due to rise in temperature low pressure area is formed over the Northern India. An intense low-pressure area develops over the ‘Maru’ area of Rajasthan and Punjab. On the contrary high pressure area develops over the Indian Ocean. During this season very hot winds blow in the Northern India, called ‘Loo’ in the local dialect. Sometimes hailstorms are accompanied by light showers.
- Rainfall: The amount of rainfall received is less in this season. It is called Kal Baisakhi in West Bengal; Mango Showers in Malabar Coast; Cherry Blossom in Coffee-producing areas.
Autumn Season (Period of Retreating Monsoon)
- The months of October-November are known as the retreating monsoon season, when there is a withdrawl of the monsoon winds from India. By October as the temperature began decreasing the low pressure zone in northern India becomes weak. Hence, the south-west monsoon winds start to retreat gradually and by early November they withdraw completely from India.
- The retreating monsoon season is indicated by a rise in temperature. This sudden change in weather conditions gives rise to tropical cyclones over the Bay of Bengal. They strike coastal Tamil Nadu, Andhra Pradesh, Odisha and the Ganga-Brahmaputra delta, causing horrible damage to life and property.
Distribution of Rainfall
The distribution of rainfall in India is not even. It varies from season to season as well as from place to place. Two factors have great influence on the distribution of rainfall. They are direction of monsoon winds and relief features. Broadly, India can be divided into four rainfall regions i.e., very heavy, heavy, moderate and scanty.
Climate of Rajasthan
- There are different types of climate in Rajasthan. They are influenced by various factors as latitude, altitude, direction of mountains, direction of winds, types of soil, vegetation, etc.
- Summer, rainy and winter are three main seasons in Rajasthan.
According to Meterological Department
- Winter Monsoon period:
- 1. Winter season- December to February.
- 2. Summer season- March to mid-June.
- Summer Monsoon period:
- 1. Rainy season – Mid-June to mid-September.
- 2. Autumn season- Mid-September to December.
Climate : Long-term seasonal conditions of a region.
Extreme : Too hot or cold
Monsoon : Rainy weather
Jet Steam : Strong winds blowing in the troposphere (layer) of the atmosphere
Troposphere: Lowest layer of the earth