9.2.g.4 climate

15/04/2023 R. Ezhilraman, PGT-Social Science 1

R. Ezhilraman

PGT-Social Science

JNV Lepakshi

Subject: Geography

For Class: IX

What is Climate?Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It refers to the sum total of weather conditions and variation over a large area for a long period of time.It is the long-term weather of that area which remains at least 30 years.


Weather refers to the state of atmosphere over an area at any point of time. The elements of both weather and climate are same. It is the combination of temperature, humidity, precipitation, wind, cloudiness and other atmospheric conditions at a specific time.

What is Weather?


Monsoon

The word monsoon is derived from the Arabic word ‘mausim’ which literally means season.‘Monsoon’ refers to the seasonal reversal in the wind direction during a year.The World is divided into a number of Climatic Regions. The Climate of India is described as the ‘monsoon’ type. This type of climate is found in South and Southeast Asia. But, there are perceptible regional variations in climatic conditions within the country. Two important elements viz., temperature and precipitation, often vary from place to place and season to season.


Difference in Temperature

In summer, the temperature in parts of Rajasthan Desert is 50°C, and it is around 20°C in Pahalgam in J & K. On a winter night, temperature at Drass in J & K may less than -45°C, and at Tiruvananthapuram it may be of 22°C.

In some places temperature between day and night temperature differs. In the Thar Desert, it rise to 50°C, in day and drop down to near 15°C in night. But in the Andaman and Nicobar islands or in Kerala, there is no much difference in day and night temperatures.


Precipitation

Precipitation varies in its form, types and amount and seasonal distribution. It is in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country. The annual precipitation varies from 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 Tamil Nadu coast gets rain during October and November.Rainfall generally decrease from east to west in the Northern Plains. These variations have given rise to variety in lives of people, their food, clothes and houses.


Vegetation


Vegetation can affect both temperature and the precipitation patterns in an area.


FACTORS AFFECTING CLIMATEFACTORS AFFECTING CLIMATE

RELATED TO LOCATION RELATED TO AIR

PRESSURE & WIND

• Latitude• Latitude

• The Himalayan Mt.

• The Himalayan Mt.• Distribution of Land & water• Distribution of Land & water

• Altitude• Altitude

• Distance from Sea

• Distance from Sea

Surface pressure & windSurface pressure & wind

Upper air circulationUpper air circulation

Western cyclonesWestern cyclones• Relief Features• Relief Features


Latitude

Latitude is the distance a place lies north or south of the equator and is measured by an imaginary line called lines of latitude.


EQUATORIAL REGION

TROPIC OF CANCER

LATITUDELATITUDE

High Temp

Low range

High Temp

Low range

High range of Temp

High range of Temp


Latitude

As latitude increases, the intensity of solar energy decreases. Due to curvature of the Earth, the amount of solar energy varies according to latitude.

In India, 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.


Tropical, Temperate and Polar Zones

• The tropical zone is between 23.5o north (the tropic of Cancer) and 23.5o south (the tropic of Capricorn) of the Equator. The Sun’s rays are most intense and the temperatures are always warm.

• The temperate zones are between 23.5o and 66.5o north and between 23.5o and 66.5o south of the Equator. The Sun’s rays strike Earth at a smaller angle than near the Equator.

• Polar zones are between 66.5o north and south latitudes and the poles. The sun’s rays strike Earth at a very small angle in the polar zones.


Highland Climates


In general, highland climates are cooler and wetter than nearby areas at lower elevations.

Earth’s Major Climate Zones


North Frigid Zone

Temperate Zone

Temperate Zone

South Frigid Zone

Torrid Zone


AGRA160C in Jan

AGRA160C in Jan

DARJILING40C in January

DARJILING40C in January

ALTITUDEALTITUDE

HIGH ALTITUDEHIGH ALTITUDE

LOW ALTITUDELOW ALTITUDE

Temperature decreased from low to high altitudeTemperature decreased from low to high altitude

Dec

reas

e in

Tem

pera

ture


Air Temperature decreases with altitude.

As elevation increases, the air gets cooler because of the energy drawn from the surroundings.


Factors That Affect Climate

Water Bodies

Large bodies of water such as lakes and oceans have an important effect on the temperature of an area because the temperature of the water body influences the temperature of the air above it.

Atmospheric Circulation

Global winds are another factor that influences climate because they distribute heat and moisture around Earth.


Solar Activity

When the Sun is most active, it contains dark blemishes called sunspots. The formation of sunspots appears to correspond with warm periods in Europe and North America.

Earth MotionsGeographic changes in Earth’s land and water bodies cause changes in climate. Changes in the shape of Earth’s orbit and the tilt of Earth on its axis are other Earth motions that affect global climates.

Natural Processes That Change Climates


Human Impact on Climate Changes

The Greenhouse Effect

The greenhouse effect is a natural warming of both Earth’s lower atmosphere and Earth’s surface from solar radiation being absorbed and emitted by the atmosphere.

Global Warming

As a result of increased levels of carbon dioxide and other greenhouse gases, global temperatures have increased. This increase is called global warming.


The Pressure and Surface Winds

The pressure and wind system of any area depend on the latitude and altitude of the place. It influences the temperature and rainfall pattern.The climate and weather conditions in India are governed by the atmospheric conditions like:• Pressure and surface winds;• Upper air circulation; and• Western cyclonic disturbances and tropical cyclones.India lies in the north easterly winds region. These winds originate from the subtropical high-pressure belt of the northern hemisphere. They blow south, get deflected to the right due to the Coriolis force and move towards equatorial low-pressure area.


NORTH-EAST TRADE WIND

SOUTH-EAST TRADE WIND

INTER TROPICAL CONVERGENCE ZONE

SUB TROPICAL HIGH PRESSURE

SUB TROPICAL HIGH PRESSURE

SUB TROPICAL LOW PRESSURE

SUB TROPICAL LOW PRESSURE

POLAR HIGH

POLAR HIGH

SURFACE WINDSURFACE WIND


AIR MASSES CIRCULATE GLOBALLY


• At the Equator, temperatures are relatively high. Land and water masses heat up and as a result these warm the air over them.

• Air heated at the equatorial region rises to the top of the atmosphere.

• More air rising beneath it forces the air mass to spread north and south toward the poles.

Coriolis Effect• The rotation of the Earth causes all moving

objects in the Northern Hemisphere, including air mass, to deflect to the right and those in the Southern Hemisphere to move to the left.

• This Coriolis effect is absent at the Equator.• Coriolis Force- prevents a direct simple flow

from the Equator to the Poles.• This is also known as ‘Ferrel’s Law’.15/04/2023 R. Ezhilraman, PGT-Social Science 25

15/04/2023R. Ezhilraman, PGT-Social Science

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The Pressure and Surface Winds in India

The pressure and wind conditions in India is unique. During winter, there is a high-pressure in the 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 and in north-western 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.


ARABIAN SEA

ARABIAN SEA

BAY OF BENGALBAY OF BENGAL

INDIAN OCEANINDIAN OCEAN

LOW AND HIGH PRESSURELOW AND HIGH PRESSURE

LOW PRESSURE IN SUMMER

HIGH PRESSURE IN WINTER


MUMBAIMUMBAI

CHENNAICHENNAI

KOLKOTAKOLKOTA

DELHIDELHI

SIMLASIMLA

DISTANCE FROM SEADISTANCE FROM SEA

Coastal areas have equable climate where as Interior parts have extreme climate.

Coastal areas have equable climate where as Interior parts have extreme climate.


Relief

• Relief too 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.


Monsoo

n Wind

Monsoo

n Wind

Monsoo

n Wind

Receives high rainfall

Receives low rainfall

RELIEFRELIEF

Western G

hat Mt.


RELIEF

The Rain Shadow Effect


THE

HIM

ALA

YAS-

CLI

MAT

IC B

AR

RIE

R

THE

HIM

ALA

YAS-

CLI

MAT

IC B

AR

RIE

R

Mo

nso

on

Win

d

Mo

nso

on

Win

d

Mo

nso

on

Win

d

Mo

nso

on

Win

d

Co

ld W

aveC

old

Wave

Co

ld W

ave

Co

ld W

ave


Jet Stream

• The upper air circulation in India is dominated by a westerly flow, known as the jet stream.

• 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.

• Many jet streams have been identified. The most constant are the mid-latitude and the sub tropical jet stream.


TIBET

JET STREAM IN WINTERJET STREAM IN WINTER


Jet Stream

Jet streams are located at 27°-30° north latitude, 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 tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer.


JET STREAM IN SUMMERJET STREAM IN SUMMER


Western Disturbances

• 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.

• Thus very often the coast of Orissa and Andhra Pradesh are affected by those disasters.


Mediterranean seaMediterranean sea

WESTERN DISTURBANCEWESTERN DISTURBANCE


OCEAN CURRENTS

Solar energy, wind, and Earth’s rotation creates Ocean currentsCurrent- the systematic patters of water movement.Gyres- two great circular water motion.

Northern Hemisphere- the ocean current moves clockwise. Southern Hemisphere- the ocean current move anti-clockwise.

Trade winds push warm surface waters westward at the equator.

As the waters encounter the continents, they split into north- and south-flowing currents along the eastern coast, forming north and south gyres.


Surface Water blown by the winds at point A will weirs to the right of its initial path and continue eastward. Water at point B weirs to the right and continues westward.




Winds driven by uneven solar heating and Earth’s spin, drive the movement of the ocean’s surface currents. The prime movers are the powerful westerlies and the persistent trade winds (easterlies)


The Köppen climate classification system uses

mean monthly and annual values of temperature and precipitation to classify climates.

According to the Köppen classification, the earth can be divided into several major climatic zones and bands:

The Köppen Climate Classification System

Tropical climate Subtropical climate Arid climate Equatorial climate Semiarid climate Mediterranean climate

Temperate climate Oceanic climate Continental climate Subarctic climate Polar climate Climate of Antarctica


Tropical Climate


Subtropical Climate


Arid Climate


Equatorial Climate


Semiarid Climate


Mediterranean Climate


Temperate Climate


Oceanic Climate


Continental Climate


Subarctic Climate


Polar Climate


Polar Climate15/04/2023 R. Ezhilraman, PGT-Social Science 57

Polar climates are those in which the mean temperature of the warmest month is below 10oC.

Climate of Antarctica


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


Facts of Mechanism of the Monsoons


In India, the monsoons are experienced in the tropical area roughly between 20°N and 20°S. The Following facts are the Mechanism of the Monsoons.

(a)The differential heating and cooling of land and water creates low pressure on the landmass of India while the seas around experience comparatively high pressure.

(b) 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).

Inter Tropical Convergence Zone (ITCZ)


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.

Facts of Mechanism of the Monsoons


(c) The presence of the high-pressure area, east of Madagascar, nearly at 20°S over the Indian Ocean. The intensity of this high-pressure area affects the Indian Monsoon.(d) The Tibetan plateau gets intensely heated during summer, results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.(e) The movement 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.

Southern Oscillation


The changes in the pressure conditions over the southern oceans also affect the monsoons. When the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. But sometimes, 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 in Pacific Ocean and Darwin in northern Australia of Indian Ocean is predicted the intensity of the monsoons. If the pressure differences were negative, it would mean below average and late monsoons. A feature connected with the SO is the El 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 El Nino. Hence, the phenomenon is referred to as ENSO (El Nino Southern Oscillations).

DarwinTahiti

SOUTHERN OSCILLATIONSOUTHERN OSCILLATION


Effect of El Niño


El Nino 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.

Homboldt Cold Current

EL-NINO EFFECTSEL-NINO EFFECTS

Peru

1990 Delay in Monsoon

Equatorial Warm Current

El-Nino


Beginning of the Monsoon


The duration of the monsoon is between 100-120 days from early June to mid-September.

During its arrival, the normal rainfall increases suddenly and continues constantly for several days. This is known as the ‘burst’ of the monsoon, and can be distinguished from the pre-monsoon showers.

The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June.

Subsequently, it proceeds into two – (i) the Arabian Sea branch and (ii) the Bay of Bengal branch.

Beginning of the Monsoon


The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10th of June. This is a fairly rapid advance.

The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June. The lofty mountains causes the monsoon winds to deflect towards the west over the Ganga plains.

By mid-June the Arabian Sea branch of the monsoon arrives over Saurashtra-Kuchchh and the central part of the country. The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the north-western part of the Ganga plains.

Delhi generally receives the monsoon showers from the Bay of Bengal branch by the end of June (tentative date is 29th of June). By the July first week, western Uttar Pradesh, Punjab, Haryana and eastern Rajasthan experience the monsoon. By mid-July, the monsoon reaches Himachal Pradesh and the rest of the country.


End of the Monsoon


Withdrawal or the retreat of the monsoon is a more gradual process. The withdrawal of the monsoon begins in north-western states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. Then it quickly withdraw from the southern half of the peninsula. By early December, the monsoon has totally withdrawn from the country.

The islands receive the very first monsoon showers, from south to north, between the last week of April and the first week of May. Then it withdraw from north to south during the first week of December to the first week of January. By this time, the other parts of the country is already influencing the winter monsoon.


The Seasons

RHYTHM OF SEASONSRHYTHM OF SEASONS

COLD WEATHERCOLD WEATHER

RETREATING MONSOONRETREATING MONSOONHOT WEATHERHOT WEATHER

SOUTH WEST MONSOONSOUTH WEST MONSOON

Let us discuss each of them individuallyLet us discuss each of them individually

15/04/2023R. Ezhilraman, PGT-Social Science 75

The Four Main Seasons


76

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. But, the coastal areas do not experience much variation in temperature though there is variation in rainfall pattern.

In India, Four main seasons can be identified:(i) the cold weather season, (ii) the hot weather season, (iii)the advancing monsoon and (iv) the retreating monsoon with some regional variations.

COLD WEATHER SEASONCOLD WEATHER SEASON

►It extends from December to February.

►Vertical sun rays shift towards southern hemisphere.

►North India experiences intense cold where as this season is not well defined in south India.

►Light wind blow makes this season pleasant in south India.

►Occasional tropical cyclone visit eastern coast in this season.

►It extends from December to February.

►Vertical sun rays shift towards southern hemisphere.

►North India experiences intense cold where as this season is not well defined in south India.

►Light wind blow makes this season pleasant in south India.

►Occasional tropical cyclone visit eastern coast in this season.

Tropical Cyclone


The Cold Weather Season (Winter)


78

The cold weather season begins from mid- November in northern India and stays till February. December and January are the coldest months. The temperature decreases from south to the north. The average temperature of Chennai, on the eastern coast is between 24°-25° Celsius, while in the northern plains, it ranges between 10°-15° Celsius. Days are warm and nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall.

During winter, the northeast trade winds blow from land to sea. So, most part of the country faces a dry season. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as, trade winds blow from sea to land.

In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area. Influenced by the relief, these winds blow through the Ganga valley from the west and the northwest. The weather is normally marked by clear sky, low temperatures and low humidity and feeble, variable winds.

250C

250C

200C

200C200C

150C

200C

100C`

TEMPERATURE- JANUARYTEMPERATURE- JANUARY


PRESSURE- JANUARYPRESSURE- JANUARY

10191018

1018

1018

101710161015

1014

HIGH PRESSURE


Characters of the Winter Season


81

In the northern plains, there is the inflow of cyclonic disturbances from the west and the northwest. These low-pressure systems, from the Mediterranean Sea and western Asia and move into India, along with the westerly flow. They cause the winter rains (locally known as ‘mahawat’) over the plains and snowfall in the mountains. Although the amount of rainfall is small, it is more importance for cultivating the ‘rabi’ crops.

But, the peninsular region does not have a well-defined cold season. There is rare seasonal change in temperature pattern during winters due to the moderating influence of the sea.

Ganga

Delta

Northern Plain

WIND DIRECTION- WINTERWIND DIRECTION- WINTER

Bay of Bengal


WINTER RAINFALLWINTER RAINFALL

RAINFALL DUE TO WESTERN

DISTURBANCES

RAINFALL DUE TO NORTH EAST

WIND


Winter Winter is cold.

Children dress warmly to play in the snow.

Animals head to their winter homes.


HOT WEATHER SEASONHOT WEATHER SEASON

► It extends from March to May.

► Vertical sun rays shift towards Northern hemisphere.

► Temperature rises gradually from south to north.

► Highest Temperature experiences in Karnataka in March, Madhya Pradesh in April and Rajasthan in May.

► It extends from March to May.

► Vertical sun rays shift towards Northern hemisphere.

► Temperature rises gradually from south to north.

► Highest Temperature experiences in Karnataka in March, Madhya Pradesh in April and Rajasthan in May.

March 300CMarch 300C

April 380CApril 380C

May 480CMay 480C


Hot Weather Season


86

Due to the apparent northward movement of the Sun, the global heat belt shifts northward. So, from March to May, it is hot weather season in India. In March, the highest temperature is about 38°C, in Deccan plateau. In April, temperatures in Gujarat and Madhya Pradesh are around 42°C. In May, 45°C temperature is common in the north-western parts of the country. In peninsular India, temperatures remain lower due to the moderating influence of the oceans.

The summer months experience rising temperature and falling air pressure in the northern part of the country. By 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 in the east and southeast. Circulation of air begins to set in around this trough.

TEMPERATURE- JULYTEMPERATURE- JULY

200C

250C

300C

20 0C

300C25 0C

30 0C


PRESSURE- JULYPRESSURE- JULY

997

998 999100

0 10011002

1003 100

4100

5

100

6100

7


LOOLOO

KALBAISAKHIKALBAISAKHI

BARDOLI CHHEERHABARDOLI

CHHEERHA

MANGO SHOWERMANGO

SHOWER

BLOSSOM SHOWER

BLOSSOM SHOWER

STORMS IN HOT WEATHER SEASONSTORMS IN HOT WEATHER SEASON


Features of the Hot Weather Season


90

An important feature of the summer season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day, sometimes till late evening over the north and North-western India. Direct exposure to these winds may be harmful. Dust storms are very common during 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. In West Bengal, these storms are known as the ‘Kaal Baisakhi’.

By 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’.

Summer Long, hot days.

Summer fruit and vegetables are ready to be picked.

You see many bees and butterflies fly flower to flower.


Advancing Monsoon (The Rainy Season) SOUTH WEST MONSOON SEASON

Advancing Monsoon (The Rainy Season) SOUTH WEST MONSOON SEASON

► It extends from June to September.

► Intense heating in north west India creates low pressure region.

► Low pressure attract the wind from the surrounding region.

► After having rains for a few days sometime monsoon fails to occur for one or more weeks is known as break in the monsoon.

► It extends from June to September.

► Intense heating in north west India creates low pressure region.

► Low pressure attract the wind from the surrounding region.

► After having rains for a few days sometime monsoon fails to occur for one or more weeks is known as break in the monsoon.

HIGH TEMPERATURELOW PRESSURE


INTER TROPICAL CONVERGENCE ZONEEQUATOR

MONSOON WINDMONSOON WIND

SE Tra

de

SE Tra

de

SE Tra

de

SE Tra

de

Arabian sea Branch

Arabian sea Branch

Bay of Bengal Branch

Bay of Bengal Branch


ONSET OF SW MONSOONONSET OF SW MONSOON

1st J

une

5th Ju

ne10th Ju

ne

15th J

une

1st J

uly

15th Ju

ly


Advancing Monsoon (The Rainy Season)


By early June, the low-pressure condition over the northern plains attracts the trade winds of the southern hemisphere. These south-east trade winds originate over the warm subtropical areas of the southern oceans. These winds are strong and blow at an average velocity of 30 kmph. With the exception of the extreme north-west, the monsoon winds cover the country in about a month.

The south-west monsoon entirely changes the weather in India. The Western Ghats receives heavy rainfall, more than 250 cm. The rain shadow areas like Deccan Plateau and parts of Madhya Pradesh also receives rain. The north-eastern part of the country receives the maximum rainfall. Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world. Rainfall in the Ganga valley decreases from the east to the west. Rajasthan and parts of Gujarat get scanty rainfall.

Breaks in Rainfall


The monsoon rains take place only for a few days at a time. They are interspersed with rainless intervals. These breaks in monsoon are related to the movement of the monsoon trough. The trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall. Whenever the axis shifts closer to the Himalayas, widespread rain occur in the mountainous catchment areas of the Himalayan rivers, which also cause floods. The frequency and intensity of tropical depressions determine the amount and duration of monsoon rains. These depressions form at the Bay of Bengal and cross over to the mainland. The depressions follow the axis of the “monsoon trough of low pressure”. It causes heavy floods in one part, and droughts in the other. Sometimes it disturbs the farming schedule of millions of farmers all over the country.

►It extends from October to November

►Vertical sun rays start shifting towards Northern hemisphere.

►Low pressure region shift from northern parts of India towards south.

►Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive. This is commonly known as the ‘October heat’

►It extends from October to November

►Vertical sun rays start shifting towards Northern hemisphere.

►Low pressure region shift from northern parts of India towards south.

►Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive. This is commonly known as the ‘October heat’

RETREATING MONSOON SEASONRETREATING MONSOON SEASON

LOW PRESSURE


15th

Octobe

r7th

Octobe

r30

th Sep

t.

15th S

ept.

7th S

ept.

WITHDRAWAL OF MONSOONWITHDRAWAL OF MONSOON


Distribution of Rainfall


Parts of western coast and north-eastern India receive over about 400 cm of rainfall annually. But, in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab it is less than 60 cm. Rainfall is equally low in the interior of the Deccan plateau, and east of the Sahyadris. Because of low precipitation found around Leh in Jammu and Kashmir. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region.

Based on 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. Similarly, the areas of high rainfall are often affected by floods, areas of low rainfall are drought-prone.

DISTRIBUTION OF RAINFALLDISTRIBUTION OF RAINFALL

> 200cm

100-200cm

50-100 cm

< 50cm


Spring The sun shines more and

the days begin to get warmer.

Spring is a time when baby animals are born.

Spring is a time when plants and trees wake up after a long winters nap.

Spring showers help to warm the earth, moisten the soil, helping new plants to grow.


Fall Leaves change to yellow,

orange, and red.

Picking fruit and vegetables.

Animals get ready for winter.


Monsoon as a Unifying Bond


The Himalayas protect the subcontinent from extremely cold winds from central Asia. This enables northern India to have uniformly higher temperatures when compared to other areas on the same latitudes.

Similarly, the peninsular plateau, under the influence of the sea from three sides, has moderate temperatures.

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.

The Indian landscape, its animal and plant life, its entire agricultural calendar and the life of the people, including their festivities, revolve around this phenomenon.

Hello dear ones


Thank you for your patient listening….

Yours R. Ezhilraman, PGT-Social Science, JNV Lepakshi, Ananthapur

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9.2.g.4 climate