Climate – The sum total of weather conditions and variations over a large area for a long period of time (more than thirty years) is called climate.
India is home to an extraordinary variety of climatic regions, ranging from tropical in the south to temperate and alpine in the Himalayan north, where elevated regions receive sustained winter snowfall.
The nation’s climate is strongly influenced by the Himalayas and the Thar Desert.
Continental climate:
It is experienced in the interior of the continent.
It is very hot in summer and very cold in winter, e.g., Delhi.
Maritime Climate:
It is experienced in coastal areas.
It has cool summers and mild winters, e.g., Mumbai
Weather – The state of the atmosphere over an area at any point of time is called weather.
Monsoon – The seasonal reversal in wind direction during a year is called monsoon.
This type of climate is mainly found in the south and Southeast Asia.
The climate of India is of monsoon type.
Weather and Climate:
The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity and precipitation.
You may have observed that the weather conditions fluctuate very often even within a day.
But there is some common pattern over a few weeks or months, i.e. days are cool or hot, windy or calm, cloudy or bright, and wet or dry.
On the basis of the generalised monthly atmospheric conditions, the year is divided into seasons such as winter, summer or rainy seasons.
|
Weather
|
Climate
|
|
It refers to the atmosphere conditions that exist for a given time in a specific area.
|
Climate is the aggregate of day to day weather condition over a long period of time.
|
|
It refers to a small area.
|
Climate refers to a large area.
|
|
It may change at a very short interval of time.
|
Climate remains more or less unchanged year after year
|
|
It is influenced by any one of its predominant elements i.e. temperature, humidity. wind, precipitation etc.
|
It is the collective effect of all its elements.
|
Climate of India:
The climate of India is described as the ‘monsoon’ type.
In Asia, this type of climate is found mainly in the south and the southeast.
Despite an overall unity in the general pattern, there are perceptible regional variations in climatic conditions within the country.
Let us take two important elements – temperature and precipitation, and examine how they vary from place to place and season to season.
In summer, the mercury occasionally touches 50°C in some parts of the Rajasthan desert, whereas it may be around 20°C in Pahalgam in Jammu and Kashmir.
On a winter night, temperature at Drass in Jammu and Kashmir may be as low as minus 45°C.
Thiruvananthapuram, on the other hand, may have a temperature of 22°C.
There are variations not only in the form and types of precipitation but also in its amount and the seasonal distribution.
While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country.
The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan.
Most parts of the country receive rainfall from June to September.
But some parts like the Tamil Nadu coast gets a large portion of its rain during October and November.
In general, coastal areas experience less contrasts in temperature conditions.
Seasonal contrasts are more in the interior of the country.
There is decrease in rainfall generally from east to west in the Northern Plains.
These variations have given rise to variety in lives of people – in terms of the food they eat, the clothes they wear and also the kind of houses they live in.
Do you know?
In certain places there is a wide difference between day and night temperatures.
In the Thar Desert the day temperature may rise to 50°C, and drop down to near 15°C the same night.
On the other hand, there is hardly any difference in day and night temperatures in the Andaman and Nicobar islands or in Kerala.
Climate Controls:
There are six major controls of climate of any place. They are
Latitude:
Due to the curvature of the earth, the amount of solar energy received varies according to latitude As a result, air temperature generally decreases from the equator towards the poles.
Altitude:
As one goes from the surface of the earth to higher altitudes the atmosphere is less dense and temperature decreases. The hills are therefore cooler during summers.
The Pressure and Winds:
The System of any area depends on the latitude and altitude of the place thus it influence the temperature and rainfall pattern.
Distance from the Sea:
The sea exerts a moderating influence on climate.
As the distance from the sea increases, its moderating influence decreases and the people experience extreme weather conditions.
This condition is known as continentality (i.e. very hot during summers and very cold during winters).
Ocean Current:
Ocean current along with on shore winds affect the climate of the coastal areas.
For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.
Relief features:
It plays a major role in determining the climate of a place.
High mountains act as barriers for cold or hot winds.
They may also cause precipitation if they are high enough and lie in the path of rain bearing winds.
The leeward side of mountains remains relatively dry.
Factors Affecting the Climate of India:
Latitude:
The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh in the west to Mizoram in the east.
Almost half of the country, lying south of the Tropic of Cancer, belongs to the tropical area.
All the remaining area, north of the Tropic, lies in the sub-tropics.
Therefore, India’s climate has characteristics of tropical as well as subtropical climates.
Altitude:
India has mountains to the north, which have an average height of about 6,000 metres.
India also has a vast coastal area where the maximum elevation is about 30 metres.
The Himalayas prevent the cold winds from Central Asia from entering the subcontinent.
It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to central Asia.
Pressure and winds:
The climate and associated weather conditions in India are governed by the following atmospheric conditions.
- Pressure and surface winds
- Upper air circulation
- Western cyclonic disturbances and tropical cyclones
Coriolis force – An apparent force caused by the earth’s rotation is called Coriolis force.
The Coriolis force is responsible for deflecting winds towards the right in the northern hemisphere and towards the left in the southern hemisphere. This is also known as ‘Ferrel’s Law’.
India lies in the region of north easterly winds.
These winds originate from the subtropical high-pressure belt of the northern hemisphere.
They blow southwards, get deflected to the right due to the Coriolis force, and move towards the equatorial low-pressure area.
Generally, these winds carry little moisture as they originate and blow over land.
Therefore, they bring little or no rain.
Hence, India should have been an arid land, but it is not so.
The pressure and wind conditions over India are unique.
During winter, there is a high-pressure area north of the Himalayas.
Cold dry winds blow from this region to the low-pressure areas over the oceans to the south.
In summer, a low-pressure area develops over interior Asia, as well as, over northwestern India.
This causes a complete reversal of the direction of winds during summer.
Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator, and turns right towards the low-pressure areas over the Indian subcontinent.
These are known as the Southwest Monsoon winds.
These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the mainland of India.
Winds especially Typhoons, Air current and Monsoon also have a great bearing on the climate of India.
Typhoons originating in the China Sea also have a great bearing on the weather conditions in India.
Jet Stream – Fast flowing and narrow air currents are called jet streams.
These are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere.
Their speed varies from about 110 km/h in summer to about 184 km/h in winter.
A number of separate jet streams have been identified.
The most constant are the mid-latitude and the sub-tropical jet stream.
These jet streams are located approximately over 27°-30° north latitude, therefore, they are known as subtropical westerly jet streams.
Over India, these jet streams blow south of the Himalayas, all through the year except in summer.
The western cyclonic disturbances experienced in the north and north-western parts of the country are brought in by this westerly flow.
In summer, the subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun.
An easterly jet stream, called the sub-tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer months.
Western Cyclonic Disturbance:
The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region.
They usually influence the weather of the north and north-western regions of India.
Tropical cyclones occur during the monsoon, as well as, in October – November, and are part of the easterly flow.
These disturbances affect the coastal regions of the country.
Distance from the Sea:
The location of seas on the three sides of India has exerted a moderate influence on much of the, Indian sub continent.
As the distance from the sea increases its moderating influence decreases.
Physiography:
It plays an important role in determining the climate of a place.
The location of the Himalayas in the north has acted as a great barrier to the cold winds of the north.
But for the Himalayas, India would have become a cold country.
The Indian Monsoon:
The climate of India is strongly influenced by monsoon winds.
The sailors who came to India in historic times were one of the first to have noticed the phenomenon of the monsoon.
They benefited from the reversal of the wind system as they came by sailing ships at the mercy of winds.
The Arabs, who had also come to India as traders named this seasonal reversal of the wind system ‘monsoon’.
Atmospheric Conditions over the Indian Subcontinent in the Month of January
Atmospheric Conditions over the Indian Subcontinent in the Month of June
Isobar – An imaginary line, drawn on the map, to join places having the same pressure above sea level is called isobar.
It is measured in millibar (mb).
Isohyet – An imaginary line, drawn on the map, to join places having the same amount of rainfall, e.g., mm or cm is called Isohyet.
The monsoons are experienced in the tropical area roughly between 20° N and 20° S. To understand the mechanism of the monsoons, the following facts are important.
The differential heating and cooling of land and water
The differential heating and cooling of land and water creates low pressure on the landmass of India while the sea around experience comparatively high pressure.
The shift of the position of Inter Tropical Convergence Zone (ITCZ):
The shift of the position of Inter Tropical Convergence Zone (ITCZ) in summer, over the Ganga plain.
This is the equatorial trough normally positioned about 5°N of the equator.
.It is also known as the monsoon trough during the monsoon season.
The presence of High Pressure Area:
The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean.
The intensity and position of this high-pressure area affects the Indian Monsoon.
The Tibetan Plateau:
The Tibetan Plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.
The movements of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.
Inter Tropical Convergence Zone:
The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes.
This is where the northeast and the southeast trade winds converge.
This convergence zone lies more or less parallel to the equator but moves north or south with the apparent movement of the sun.
Southern Oscillation or SO:
When the tropical eastern South Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure.
But in certain years, there is a reversal in the pressure conditions and the eastern Pacific has lower pressure in comparison to the eastern Indian Ocean.
This periodic change in pressure conditions is known as the Southern Oscillation or SO.
The difference in pressure over Tahiti (Pacific Ocean, 18°S/149°W) and Darwin in northern Australia (Indian Ocean, 12°30’S/131°E) is computed to predict the intensity of the monsoons.
If the pressure differences were negative, it would mean below average and late monsoons.
El Nino Southern Oscillations:
A feature connected with the SO is the El Nino phenomenon in which 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 El Nino.
Hence, the phenomenon is referred to as ENSO (El Nino Southern Oscillations).
El Nino:
This is a name given to the periodic development of a warm ocean current along the coast of Peru as a temporary replacement of the cold Peruvian current.
‘El Nino’ is a Spanish word meaning ‘the child’, and refers to the baby Christ, as this current starts flowing during Christmas.
The presence of the El Nino leads to an increase in sea-surface temperatures and weakening of the trade winds in the region
The Onset of the Monsoon and Withdrawal:
The Monsoon, unlike the trades, are not steady winds but are pulsating in nature, affected by different atmospheric conditions encountered by it, on its way over the warm tropical seas.
The duration of the monsoon is between 100- 120 days from early June to mid-September.
Breaking of monsoon:
Sudden approach of the moisture laden winds is associated with violent thunder and lightning. This is known as “break” or “burst” of the monsoons.
The monsoon first “break” on the south-west Coast of India around 1st June.
The onset of the monsoon:
The monsoon arrives at the southern tip of the Indian Peninsula general by the first week of June subsequently, it divides into two branches.
- The Arabian Sea Branch
- The Bay of Bengal Branch
The Arabian Sea branch reaches Mumbai about 10 days later on approximately the 10% of June.
This is fairly rapid advance.
The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June.
The lofty mountains cause the monsoon winds to deflect towards the west over Ganga plains.
By mid June the Arabian Sea branch of the monsoon arrives over Saurashtra Kuchchh and the central part of the country.
Both the branches of monsoon merge over the northwestern part of the Ganga plain.
Delhi receives the monsoon shower from the Bay of Bengal branch by the end of the June.
By the first week of July, western Uttar Pradesh, Punjab, Haryana eastern Rajasthan experience monsoon.
By mid July the monsoon reaches Himachal Pradesh and rest of the country.
Withdrawal of the Monsoon:
Withdrawal or the retreat of the monsoon is a more gradual process.
The monsoon begins to withdraw from the northwestern states of India by early September.
The monsoon withdraws completely from the northern part of the Indian peninsular by mid-October.
The monsoon withdraws from the rest by the country by early December.
The islands receive the very first monsoon showers from the first week of April to the first week of May; progressively from south to north.
The withdrawal of monsoon in the islands takes place from the first week of December to the first week of January.
Monsoon trough – The intense low pressure area, which develops over north-western parts of the country is called Monsoon trough.
Extending from Thar Desert to Chota Nagpur Plateau
Meteorologist – A person who studies the conditions and processes within the earth s atmosphere. e.g. air pressure, temperature, wind speed, cloud formation etc. is called Meteorologists.
Meteorologists predict likely future weather patterns.
Leeward side – The rain shadow area and lies on the side which is away from the direction of the wind is called Leeward side.
E.g., Deccan Plateau is on the leeward side of the Western Ghats.
The Seasons – A division of the year based on changes in weather, ecology, and the number of daylight hours in a given region is called season.
The monsoon type of climate is characterised by a distinct seasonal pattern.
The weather conditions greatly change from one season to the other.
These changes are particularly noticeable in the interior parts of the country.
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, the hot weather season, the advancing monsoon and the retreating monsoon with some regional variations.
The Cold Weather Season (winter):
The cold season begins from mid-November till February.
The temperature decreases from south to the north.
The average temperature of Chennai is between 24° to 25° Celsius.
While in the northern plains, it is between 10° to 15° Celsius.
Days are warm; nights are cold.
Higher slopes of Himalayas experience snowfall.
North-east trade winds blow over the country.
They blow from land to sea.
For most parts of the country, it is dry season.
Tamil Nadu gets rain from these winds; here they blow from sea to land.
Western Disturbances (cyclonic disturbances) move into India from the Mediterranean Sea and blow over northern and North-western parts of India.
They cause much needed winter rains over the northern plains and snowfall in the Himalayas. Srinagar also experiences snowfall during this season.
The total amount of rainfall is about 70 cm.
They are important for the cultivation of Rabi crops.
Locally these rains are also known as “Mahawat”.
The peninsular region does not have a well-defined cold season.
Due to the moderating influence of the sea, there is not much noticeable seasonal changes in temperature pattern in winters.
The Hot Weather Season (summer):
During this period there is a rapid shifted belt of heat from south to north.
In May, the rising temperature leads to a low pressure in wide areas from the Thar Desert to Chota Nagpur Plateau.
Jaisalmer being the hottest.
Because of this low pressure, the moisture laden winds from the Arabian Sea are attracted towards this area and consequently there is rainfall.
A 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.
Uttar Pradesh in the north suffers from loo.
Sometimes they even continue until late in the evening.
Direct exposure to these winds may even prove to be fatal.
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.
This is also the season for localised thunderstorms, associated with violent winds, torrential downpours, often accompanied by hail.
In West Bengal, these storms are known as the ‘Kaal Baisakhi’ calamity for the month of Baisakh.
Towards the close of the summer season, pre-monsoon showers are common especially in Kerala and Karnataka.
They help in the early ripening of mangoes and are often referred to as “Mango Showers’.
Advancing Monsoon Season (The Rainy Season):
This season runs from June to September.
During these months the south west monsoon winds blow northwards into two branches from the Arabian Sea and the Bay of Bengal.
They make rainfall almost in the whole of northern India.
These winds blow from the oceanic high pressure area towards the low pressure area of land and make heavy rainfall.
The Arabian Sea branches causes heavy rainfall in the coastal areas of the Western Ghats but this rainfall decreases as the monsoon go further.
Kutch receives less rain fall.
The Bay of Bengal causes heavy rain fall in the hills of Meghalaya Mawsynram receives highest rainfall in the world.
As the monsoon winds take a turn from east to west because of Himalayas, the rain goes on decreasing.
Due to the uncertainty and uneven distribution of rainfall, floods and droughts are common during this season.
Another phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall.
These breaks in monsoon are related to the movement of the monsoon trough.
When the axis of the monsoon trough lies over the plains, rainfall is good in these parts.
On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains and widespread rain occurs in the mountainous catchment areas of the Himalayan Rivers.
These heavy rains bring in their wake, devastating floods causing damage to life and property in the plains.
The frequency and intensity of tropical depressions too, determine the amount and duration of monsoon rains.
These depressions form at the head of the Bay of Bengal and cross over to the mainland.
The Retreating Monsoon (The Transition Season):
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 temperature is high, nights are cool and pleasant.
The land is still moist.
Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day.
This is commonly known as ‘October heat’.
In the second half of October, the mercury begins to fall rapidly in northern India.
At this time the monsoon starts retreating.
The lower temperature on the plains give rise to gradual increase in pressure and as such the monsoons, retreat from most parts of North India.
Depressions originate in the southern part of the Bay of Bengal and start moving towards the east coast of India.
Tamil Nadu receives high rainfall from these winds during these seasons.
The distribution and, the range of rainfall is not certain even during this season also.
Do you know?
Mawsynram, the wettest place on the earth is also reputed for its stalagmite and stalactite caves.
Distribution of Rainfall:
The Western Coast mid North Eastern, India receives over about 400 cm of rainfall annually.
Western Rajasthan and adjoining parts of Gujarat receive less than 60cm.
Rainfall is equally low in the interior of the Deccan plateau and east of the Sahyadris.
A third area of low precipitation is around Leh in Jammu and Kashmir.
The rest of the country receives moderate rainfall.
Snowfall is restricted to the Himalayan region.
Owing to 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 the leeward side of the Western Ghats.
As such, while areas of high rainfall are liable to be affected by floods, areas of low rainfall are drought-prone.
Monsoon as a Unifying Bond:
Effect of the Himalayas:
The Himalayas extending from North West to north east act as a great meteorological barrier.
These high mountains lend the entire country, a somewhat tropical touch.
For example the temperature is almost uniformly high throughout India during most of the year, especially during the summer months.
The Himalaya act as a closed base with, which the monsoon winds blow and show their unique performances.
Effects of the Monsoon:
Moreover, the all pervading effects of the monsoons on the Indian subcontinent have also lent unity to India.
With few exceptions here and there.
India gets most of its rainfall due to these common winds and that to in the summer season.
The concentration of rainfall over few months in a year keeps the whole land water-thirst for a greater part of the year.
This thirst for water is universal throughout India.
Hence, the need for developing the different means of Irrigation (such as canals, wells, tube-well, etc) is felt all over India.
Thus the vagaries (uncertainties) of monsoons are felt all over the country.
Southwest India:
The most pleasant weather is from November to March Monsoon rains between late April and July Summer temperatures hot as high as Northern India although humidity is extreme.
Cooling breezes on coast.
Inland, Mysore and Bijapur have pleasant climates with relatively low rainfall
