CLIMATE - GEOGRAPHY NOTES
CLIMATE
Climate refers to the sum total of weather conditions and variations over a large area for a long period of time.
It is the sum total of weather conditions for larger area.
Eg: for a country:
WEATHER:
It refers to state of atmosphere over an area at any point of time.
It is the total of weather conditions for limited area.
Eg: for a city
The elements of weather and climate are temperature, atmospheric pressure, wind, humidity and precipitation.
INDIAN CLIMATE•
The climate of India is monsoon type.
•Monsoon is derived from ‘mausim’which means season and it refers to the seasonal reversal in the wind direction during a year.
•In Asia, this type of climate is found mainly in south and south-east.
DIFFERENCES IN INDIAN CLIMATE
In summer the temperature of Rajasthan is about 50’C but in Jammu & Kashmir it’s 20’c.
In winter at J&K the temperature is -45’C but in Thiruvanantapuram its 22’C.
While precipitation is in the form of snowfall in upper parts of Himalyas, it rains over the rest of country.
Most parts receive rainfall from June to July but some like Tamil Nadu receive it even in the season of October and November.
CLIMATIC CONTROLS
The major controls of climate are:
1.Latitude : Due to curvature the amount of solar energy received varies according to it.
2.Altitude: As we go higher there is a decrease in temperature of 16’
3.Pressure and Wind system: As per latitude and altitude temperature and rainfall also influences the climate.
4.Distance from sea: The sea exerts moderating influence on climate, regions near sea experiences moderate climate.
5.Ocean Currents: It leads continentality which means very hot during summers and very cold during winters.
FACTORS AFFECTING INDIAN CLIMATE
1.Latitude:
Tropic of cancer almost divides the country in two equal parts running from Rann of Kuchh to Mizoram.
The region lying in the south of tropic of cancer is tropical whereas the region in north is in sub tropical.
Therefore India receives both tropical as well as sub-tropical climate.
2.Altitude:
India has mountains in north with average height of 6000m and coast line of about 30m.
The Himalyas act as a barrier to enter winds in India from Centeral Asia.
That’s why it experiences mild winters as compare to Centeral Asia.
3.PRESSURE and WINDS
It is further devided in three parts.
•Pressure and surface winds
•Upper air circulation
•Western disturbances
Pressure and surface winds: India lies in the region of north-easterly winds which originate from northern hemispher and blow towards south but
deflected to right due to corollis force.These winds carry small silts that’s why don’t affect India’s rain.
4.Upper air circulation: Winds travel from a low pressure area to high pressure area. Air moves from indian ocean to south-east direction crossing equator and turns right towards indian subcountinent giving rain to it. The upper air circulation over warm oceans is called jet stream.
5.Western disturbances: During the time of winters in India cyclone formation takes place in ‘mediterranean sea’whose winds are very powerful that after crossing Pakistan, Afghanistan they finally reach jammu and kashmir leads to rainfall in winters there.
The unifying influence of the monsoon on the Indian subcontinent is quite perceptible.
The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons.
Even the uncertainties of rain and uneven distribution are very much typical of the monsoon.
The Indian landscape, its animal and plant life, the people, including their festivities, revolve around this phenomenon.
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. The river valleys which carry this water also unite as a single river valley unit.
Early in the season, the windward side of the Western Ghats receives very heavy rainfall, more than 250cm.
The Deccan Plateau and parts of Madhya Pradesh also receive some amount of rain in spite of lying in the rain shadow area.
The maximum rainfall of this season is received in the north-eastern part of the country.
Rainfall in the Ganga valley decreases from the east to the west. Rajasthan and parts of Gujarat get scanty rainfall.
The breaks in the monsoon are related to the movement of the monsoon tough.
The trough and its axis keep on moving northward or southward. When the axis of the monsoon trough lies over the plains and widespread rain occur in the Himalayan Rivers.
Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.
Ques. Why is monsoon known for its “uncertainties”?
While it causes heavy floods in one part, it may be responsible for droughts in the other.
It is often irregular in its arrival and its retreat. Hence, it sometimes disturbs the farming schedule of millions of farmers all over the country.
During October-November, the monsoon trough or the low pressure trough over the northern plains becomes weaker. This is gradually replaced by a high-pressure system.
The south-east monsoon winds weaken and start withdrawing gradually. By the beginning of the October, the monsoon withdraws from the Northern Plains.
The months of October-November form a period of transition from hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and rise in temperature.
While day temperatures are high, nights are cool and pleasant.
Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day. This is known as “OCTOBER HEAT”.
The low-pressure conditions, over north-western India, get transferred to the Bay of Bengal by early November.
This shift is associated with the occurrence of cyclonic depressions, which originates over the Andaman Sea.
These cyclones generally cross the eastern coasts of India cause heavy and widesprad rain.
These tropical cyclones are often very destructive.
The thickly populated deltas of the Godavari, the Krishna and the Kaveri are frequently struck by cyclones, which cause great damage to life and property.
THE SEASONS
The monsoon type of climate is characterised by a distinct seasonal pattern.
The weather conditions greatly change from one season to the other. The coastal
areas do not experience much variation in temperature though there is variation
in rainfall pattern. Four main seasons can be identified in India- the cold weather
season, hot weather season, the advancing monsoon and the retreating monsoon
with some regional variations.
THE COLD WEATHER SEASON (WINTER)
1. The cold weather season begins from mid- November in northern India and stays
till February.
2. December and January are the coldest months in the northern part of India.
3. The temperature decreases from south to the north.
4. Days are warm and nights are cold.
5. Frost is common in the north and the higher slopes of Himalayas experience
snowfall.
6. The northeast trade winds blow from land to sea and hence, for most part of the
country, it is a dry season.
7. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as,
here they blow from sea to land.
8. The weather is normally marked by clear sky, low temperatures and low humidity
and feeble variable winds.
9. A characteristic feature of the cold weather season over the northern plains is a
the inflow of cyclonic disturbances from the west and the northwest.
10.They cause the much- needed winter rains over the plains and snowfall in the
mountains.
11.Total amount of winter rainfall locally known as ‘mahawat’ is small; they are of . immense importance for the cultivation of ‘rabi’ crops.
12. The peninsular region does not have well- defined cold season.
THE HOT WEATHER SEASON (SUMMER)
1. From March to May, it is hot weather season in India.
2. The influence of shifting of the heat belt can be seen clearly from temperature
recordings taken during March- May at different latitudes.
3. In peninsular India, temperature remain lower due to the moderating influence of the
oceans.
4.The summer months experience rising temperature and falling air pressure in the
northern part of the country.
5. Towards the end of May, an elongated low pressure area develops in the region
extending from the Thar Desert in the northwest to Patna and Chotanagpur plateau
and southeast.
6. The striking feature of the hot weather season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.
7. Dust storms are very common during the month of May in northern India. These
storms bring temporary relief as they lower the temperature and may bring light rain
and cool breeze.
8. In West Bengal, these storms are known as ‘Kaal Baisakhi’.
9. Towards the close of the summer season, pre- monsoon showers are common
especially, in Kerala and Karnataka.
DISTRIBUTION OF RAINFALL
There are three types of rainfall :-
-Low rainfall (Less than 50 cm.)
- Average rainfall (Between 50 to 250 cm.)
- High rainfall (More than 250 cm.)
1. Parts of western coast and northern India receive over about 400 cm of rainfall
annually.
2. It is less than 60cm in western Rajasthan and adjoining parts of Gujarat, Haryana and
Punjab.
3. Rainfall is equally low in the interior of Deccan plateau, and east of the Sahyadris.
4. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region.
Because of the nature of monsoons, the annual rainfall is highly variable from year to year. Variability is high in the regions of low rainfall such as parts of Rajasthan, Gujarat and leeward (rain shadow area) side of the Western Ghats. While the areas of high rainfall are responsible to be affected by the floods and the areas of low rainfall are drought- prone.
SOME IMPORTANT TERMS
1. Frost- A state in freezing, frozen dew.
2. Loo- Strong, gusty, hot, dry winds blowing during the day over the north and
northwestern India.
3. Mango showers- Pre-monsoon showers in Kerala and Karnataka help in ripening of
mangoes earlier, known as monsoon showers.
4. Trough- large vacuum in between of the Himalayas and the peninsular plateau, the
plains.
5. Leeward- Rain shadow area.
Apara Sanwaria
