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Climate of India:
The one word which can aptly describe the Indian climate is ‘Monsoon’. It is derived from the Arabic word ‘Mausim’, which means the seasonal reversal of winds.
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In winter, for six months, winds blow from land to sea.
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In summer, for six months, winds blow from sea to land.
Monsoon climate is a characteristic feature of South and South-East Asia and greatly influences the economic activities of these regions.
Indian agriculture is often considered a gamble against the monsoon because agricultural activities in almost all parts of India are highly dependent on monsoon rainfall. In fact, the monsoon is the axis around which the Indian economy revolves.
(A) South-West Monsoon (Summer Monsoon):
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During summer, the south-west monsoon winds strike suddenly on the coast of Kerala. This sudden onset is called the “Burst of Monsoon.” It usually occurs around 1st June every year.
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The monsoon advances progressively from 1st June and covers the entire country by 15th July, reaching Jaisalmer (Rajasthan).
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The monsoon is pulsating in nature. It does not produce uniform weather conditions throughout India.
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There are dry, semi-arid, and humid regions.
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Rainfall decreases as we move away from the sea.
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Rainfall during the summer season is highly variable from region to region.
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The withdrawal of the monsoon is more gradual than its arrival.
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It starts retreating from Jaisalmer around 1st September.
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It withdraws completely from India by mid-December, leaving from the east Tamil Nadu coast.
(B) North-East Monsoon (Winter Monsoon):
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During winter, while retreating, the winds become north-east winds.
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When these winds cross the Bay of Bengal, they pick up moisture and cause rainfall in the eastern coastal parts of India.
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These winds are called North-East Monsoonal Winds.
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About 40–60 cm of rainfall is received in:
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October–November in the Northern Circars region (Andhra Pradesh and Odisha coast)
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November–December along the Tamil Nadu coast
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The complete mechanism of monsoon is complex, and continuous research is being conducted to understand it better.
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North-West India (Jammu & Kashmir, Punjab, Haryana, Delhi, and Uttarakhand) receives winter rainfall due to:
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Jet Streams
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Western Disturbances
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Jet Streams:
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Jet streams are strong air currents circulating around the earth at an altitude of 6–10 km.
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Their speed ranges from 250 to 400 km per hour.
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They are about 2–4 km thick, hundreds of kilometers wide, and thousands of kilometers long.
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Jet streams are formed when the pressure gradient force becomes equal and opposite to the Coriolis force.
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They are a type of geostrophic winds.
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The westerly jet streams of the Northern Hemisphere influence the Indian climate during winter and produce light rainfall (about 2–5 cm).
Western Disturbances:
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This period extends from mid-December to February.
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During this time, a high-pressure region develops in north-western India due to the southward movement of the Sun.
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The average temperature of this region is about 10°C, whereas in South India it remains around 25°C.
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Winds blow from north-west to east, and the north-east trade winds cause rainfall in the eastern coastal parts.
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During this period, rainfall is received from Mediterranean Western Disturbances.
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These are temperate cyclones brought to India through Iraq, Iran, Afghanistan and Pakistan by the westerly jet streams.
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As these disturbances move eastward, they cause little rainfall.
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In Punjab, they give about 25 cm rainfall.
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In western Uttar Pradesh, they give about 4 cm rainfall.
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This winter rainfall is very important for Punjab, Haryana and Western Uttar Pradesh for the cultivation of wheat, gram and mustard.
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In Rajasthan, this rainfall is called “Mawat.”
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It also helps apple plantations in Himachal Pradesh.
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Regions above the snowline in Himachal Pradesh receive snowfall due to these disturbances, making rivers perennial.
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Western disturbances contribute about 3% of the total annual rainfall.
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Sometimes they cause cold waves in north-western India.
Annual Rainfall in India:
Rainfall regions are classified into three categories:
1. Regions of Heavy Rainfall:
(More than 300 cm per annum)
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Western slopes of the Western Ghats
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Eastern part of India including Meghalaya Hills
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Southern slopes of Arunachal Himalaya
2. Regions of Very Low Rainfall:
(Less than 50 cm per annum)
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Western Rajasthan (Thar Desert)
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Leh and Ladakh region of Jammu & Kashmir
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Rain-shadow area of Western Ghats in Peninsular India
3. Regions of Moderate Rainfall:
(50–300 cm per annum)
The rest of India receives moderate rainfall. The following trends are observed:
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In South India, rainfall decreases from coast towards the interior.
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In Central India, rainfall decreases from east coast towards west coast.
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In Northern India, rainfall decreases from north to south (from Himalayan mountains towards the Gangetic plains).
Flood and Drought Affected Areas:
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The regional and seasonal distribution of rainfall in India is highly uneven.
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Jaisalmer receives less than 9 cm of annual rainfall.
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Mawsynram (near Cherrapunji) receives more than 1140 cm of annual rainfall.
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Most rainfall in India occurs during June, July, August and September.
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Variations in rainfall are greater in regions where rainfall is low.
Droughts:
A drought is an abnormally long dry season that creates a clear imbalance in the availability of water. The main causes of drought are:
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Irregular or failure of monsoon
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Unscientific agricultural practices
The Irrigation Commission has classified drought-affected areas into two types:
(a) Drought Areas:
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Areas where annual rainfall is less than 50 cm
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Variability of rainfall is more than 25%
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Includes: Western Rajasthan, Saurashtra and Kachchh regions
(b) Drought-Prone Areas:
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Areas where average annual rainfall is less than 75 cm
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Negative rainfall variability is more than 25%
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Includes:
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Gujarat
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Rajasthan
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Punjab
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Haryana
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Western Uttar Pradesh
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Western Madhya Pradesh
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Central Maharashtra
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Interior Karnataka
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Rayalaseema
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Southern Telangana
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Certain parts of Tamil Nadu
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Palamau (Jharkhand)
Floods:
Flood occurs when rivers overflow their banks and spread water into adjacent areas.
Causes of Floods:
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Excessive rainfall in the catchment area of rivers
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Cyclonic rainfall in coastal areas
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Cloudbursts (causing flash floods, especially in dry regions like Rajasthan)
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Siltation of river basins
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Change in river courses
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Excessive deforestation in hill slopes
Flood Areas in India:
Areas of Maximum Frequency:
Floods occur almost every year in:
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Brahmaputra Valley
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Lower Ganga Valley
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Delta regions of Godavari, Krishna, Mahanadi, and Kaveri
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Basins of rivers like Gandak and Kosi
Areas of Medium Frequency:
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Floods occur once in five years or less
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Most flood-affected areas of India fall under this category
Areas of Minimum Frequency:
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Areas receiving less rainfall
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Floods occur due to sudden cloudbursts or poor drainage systems
El Nino:
is a warm ocean current that develops along the Peruvian coast. It greatly affects the South-West Indian Monsoon.
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Mawsynram (Khasi Hills, Meghalaya) is the second wettest place in the world after Hawaii Island (USA), followed by Cherrapunji (Meghalaya).
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Average annual rainfall of India is about 120 cm, while the world average is about 100 cm per year
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The wettest place in the world is Lloró (Colombia) with an annual precipitation of about 13,299 mm. Disclaimer:This content is prepared for educational and informational purposes only. The notes are simplified for better understanding and exam preparation (UPSC and State Exams). Readers are advised to refer to standard textbooks and official sources for detailed study
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