Detailed Chapter Notes (Part - 3) - Climate - Social Studies (SST) Class 9

Distribution Of Rainfall

• Areas of Heavy Rainfall: Areas that get rainfall of 200 cms and above are Assam, the Ganga Delta, the Western Ghats and the Western Coastal regions and the mountainous regions of Himachal Pradesh.

Distribution of RainFall 

• Areas of Moderate Rainfall: Areas that get annual rainfall between 100 cms to 200 cms are Madhya Pradesh, Orissa, Chhota Nagpur, Western Bengal, Bihar, Eastern U.P, North-Eastern Punjab; Eastern parts of Tamil Nadu and Eastern slopes of Western Ghats receive moderate rainfall.
• Areas with Low Rainfall: Areas receiving annual rainfall between 50 cms to 100 cms are the Deccan Plateau, Western U.P, South-Eastern Punjab, Eastern Rajasthan and parts of Kashmir get low rainfall.
• Areas with Scanty Rainfall: Areas that get less than 50 cms of rainfall annually are western Rajasthan, Kutch, Southeastern parts of Haryana, Northeastern Kashmir get scanty rainfall.

Consequences of the Uneven Precipitation in India

• If there is too much rain in certain areas they cause floods and havoc all around.
• Many grown-up crops, villages, railway lines are washed away resulting in great loss of men and money.
• If there are not sufficient rains even then people are doomed because of drought and hunger. 
• Many people begin to starve and die of hunger. 
• Standing crops dry away thereby bringing doom to the farmers.

Uneven distribution rainfall is due to:

• Relief / Orography
• Wind direction
• Location
• Low-pressure axis.

Monsoon as a Unifying Bond

• The unifying influence of the monsoon on the Indian subcontinent is quite noticeable.
• The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons. 
• The uncertainties of rain and uneven distribution are very much typical of the monsoons. 
• Year after year, people of India from north to south and from east to west, eagerly await the arrival of the monsoon. 
• These monsoon winds bind the whole country by providing water to set the agricultural activities in motion.

Important Points To Remember

1. Mango showers

• Mango showers are pre-monsoon showers.
• This phenomenon is observed in Kerala and coastal Karnataka.
• The mango showers help in the early ripening of, mangoes.

Regions of Mango Shower and Kal Baisakh

2. Kalbaisakhi

• Kalbaisakhi means the violent black clouds of the month of Baisakh. 
• This is the name given to the north-westerly and northerly winds in Bengal and Assam. These winds cause very heavy rains and distraction.

3. Chennai receives more rain in winter

• The northeast winds pick up moisture while crossing Bay of Bengal. these winds are onshore in the winter season.
• In the summer Chennai lies in the rain-shadow of the Western Ghats, moreover the winds are offshore, therefore receives less rainfall.

4. Break or burst of the monsoon:

• The sudden approach of the moisture-laden winds is associated with violent thunder and lightning. 
• This is known as the “break” or “burst” of the monsoons. The first ‘break’ of monsoons on the southwest coast of India is around 1^st June.

5. Southern Oscillation

• The pressure systems of the Pacific and Indian Oceans are interrelated. 
• When the pressure is high in the Pacific, there is low pressure in the Indian Ocean. The winds move from high pressure to low pressure and vice-versa. 
• This causes the shifting of winds across the equator in different seasons. this is known as the southern oscillation.

6. EI Nino Southern Oscillations 

• A feature connected with Southern Oscillation is the EI Nino, a warm ocean current that flows past the Peruvian Coast, in place of the cold Peruvian current, every 2 to 5 years. 
• The changes in pressure conditions are connected to the EI Nino, the phenomenon is referred to as ENSO (EI Nino Southern Oscillations).

7. Mawsynram receives the highest rainfall in the world:

• Mawsynram is situated at the head of a funnel-shaped valley in the Khasi hills.
• Its unique topographical location together with wind direction is responsible for causing the heaviest rainfall in the world.

8. The rainfall decreases from South to North 

• The S.W. Monsoons originates from the Indian Ocean and divides into branches due to the shape of the Indian peninsular.
• Trivandrum gets above 200 cm.
• Whereas Delhi situated in the interior gets only about 50 cm.
• The Arabian Sea branch strikes the Western Ghats and causes heavy rainfall.
• Whereas another branch of the Arabian Sea monsoon blows parallel to the Aravallis. thus jodhpur gets less than 25cms of rain.

9. The Western Ghats receive more rain from the southwest monsoons than the Eastern Ghats because:

Map showing the position of Western and Eastern Ghats

• The Arabian Sea branch of the monsoon is onshore.
• These winds are forced to rise and cause heavy rains.
• By the time these winds reach the east coast, most of the moisture is lost.
• The winds are offshore, so they are given less rain.
• The Eastern Ghats lies on the leeward/rain-shadow area, hence it gets less rain.

Indian would have been an arid land or dessert if there had been no phenomena of monsoons :

• Indian receives 75 to 90% of the rainfall from the monsoons.
• These monsoons winds occur due to the uneven heating of land and sea.
• The mighty Himalayas check the two branches of southwest monsoons, the Arabian Sea branch and the Bay of Bengal branch. 
• These, cover the whole of India thus preventing it from becoming a desert.

Important Differences Between:  

1. Equable Climate & Extreme Climate

2. Rainfall and Precipitation