• Different relief features in a vast country like India are responsible for varied climatic conditions
• India has very hot and very cold regions; as well as regions with very heavy rainfall and very scanty rainfall
• The climate of India has been influenced by its position, size and relief features
• Monsoon winds are the main factors that determine the climate of India
• A large part of India has tropical monsoon climate
The South west monsoon controls the agriculture of India, which is the main occupation of the people. When the monsoons fail, there is drought, and the crops also fail. When the monsoon is heavy, there are floods causing destruction to life and property.
MAJOR FACTORS AFFECTING INDIAN CLIMATE
• Northward shifting of the Westerly Jet (north of Himalayas)
• Northward shifting of the ITCZ.
• S-E trade winds from S. hemisphere cross the equator and turn right due to coriolis force.
• Latitudinal Extent
• Southern Seas
• Northern Mountains
• El – Nino
• La – Nina
• Westerlies in Northern part of India from Mediterranean (in winters)
• Easterlies due to Heating of Tibetian Plateau
• Jet streams
INDIAN MONSOON FEATURES
• Unique weather phenomenon
• Seasonal reversal of winds
• Sudden Onset (Sudden rain start)
• Gradual Advance
• Gradual retreat
• Variation – regional and temporal
• Monsoon is seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea.
• The southwest monsoon brings rains towards the end of summer as the high pressure built in the Indian Ocean pushes the wind masses towards the low pressure formed on land.
• Temperature Gradient – It’s the temperature variation between the sea and the landmass.
SUMMER MONSOON IN INDIA (SW MONSOON)
• Originates due to Northward shift of ITCZ – SE trade winds cross equator – Deflect & enter into India as SW Monsoon.
• Easterly Jet Stream / SE Monsoon / BOB Monsoon – Due to differential heating of Tibetian plateau & Himalayan region with respect to BOB.
• The southwest monsoon arrives in two branches: the Bay of Bengal branch and the Arabian Sea branch.
• The Bay of Bengal branch, which initially tracks the Coromandal Coast northeast from Cape Comorin to Orissa, swerves to the northwest towards the Indo-Gangetic Plains.
• The Arabian Sea branch extends toward a low-pressure area over the Thar Desert and is roughly three times stronger than the Bay of Bengal branch.
• The Arabian Sea branch moves northeast towards the Himalayas.
Initiation of Summer Monsoon- onset of the monsoon
• The southwest monsoon typically breaks over Indian Territory by around 25 May, when it lashes the Andaman and Nicobar Islands in the Bay of Bengal
• It strikes the Indian mainland around 1 June near the Malabar Coast of Kerala
• By 9 June, it reaches Mumbai; it appears over Delhi by 29 June
• By the first week of July, the entire country experiences monsoon rain
• On average, South India receives more rainfall than North India
• However, Northeast India receives the most precipitation
Arabian Sea Branch
• Strikes WGs and Move parallel to Aravallis & Strike Himalayas
• Rainfall at WGs & Coastal Regions and Northern Plains
• Strikes at Western Ghats; and gives rainfall to the western most regions
• While rain shadow interiors, the Deccan plateau receive very less rainfall.
Bay of Bengal Branch:
• Moves parallel with the Eastern Ghats and produce very less rainfall until it strikes at NE.
• Bifurcate at Meghalaya hills & move parallel to Himalaya
• One branch provide rainfall to NE India region
• Another moves westward providing rainfall to northern plains
• Going westward Rainfall Decreases
• Rainfall at Northern East plains and Northern Plains
Withdrawal of Summer Monsoon:
• Monsoon clouds begin retreating from North India by the end of August; it withdraws from Mumbai by 5 October.
• As India further cools during September, the southwest monsoon weakens. By the end of November, it leaves the country.
RETREATING OR NE MONSOON
• Around September, with the sun fast retreating south, the northern land mass of the Indian subcontinent cool off rapidly.
• With this, air pressure begins to build over northern India, but the Indian Ocean and its surrounding atmosphere still holds its heat.
• surrounding atmosphere still holds its heat Indo-Gangetic Plain towards the vast spans of the Indian Ocean south of the Deccan peninsula.
• This is known as the Northeast Monsoon or Retreating Monsoon.
WINTER RAINFALL IN SOUTH INDIA
• While travelling towards the Indian Ocean, the dry cold wind picks up some moisture from the Bay of Bengal and pours it over peninsular India and parts of Sri Lanka.
• Cities like Madras, which get less rain from the Southwest Monsoon, receive rain from this Monsoon.
• About 50% to 60% of the rain received by the state of Tamil Nadu is from the Northeast Monsoon.
• In Southern Asia, the northeastern monsoons take place from December to early March when the surface high-pressure system is strongest.
• Jet streams are currents of air high above the Earth
• They at altitudes of about 8 to 15 kilometers, located near tropopause
• The major jet streams on Earth are westerly winds (flowing west to east)
• Flow at very high speeds – 120 kmph in winters and 50 kmph in summers
• Jet streams are caused by a combination of a planet’s rotation on its axis and atmospheric heating
• Jet streams form near boundaries of adjacent air masses with significant differences in temperature, such as the polar region and the warmer air towards the equator
• All year round westerlies flow over north India south of Himalayas but in summers with shift of the sun they flow north of Himalayas & replaced by easterlies.
Sub-tropical jet stream
• They prevail over the lower latitudes of westerlies.
• It is produced by the rotation of earth and its spherical shape.
• The air over equator has the highest velocity (Coriolis effect)
• As it rises and moves towards north, it has a higher velocity than the air at lower altitude prevailing at same latitude
• So it begins to flow from west to east around 300 latitude.
Sub-Tropical Westerly Jet:
• Winter – entirely south of Himalayas – over north India
• Major cause of western disturbance
• STWJ maintain the High pressure over north India
• Hence no Monsoon in winters
• During summers it flows to the north of Himalayas
• Hence low pressure over north India & monsoon
– Tropical Easterly Jet Stream which is associated closely with the burst of monsoon. It is also a major reason why there are no cyclones during Monsoon because the presence of an Easterly jet over the Indian landmass in the upper troposphere prevents vertical circulation of air, which is a pre-condition for formation of cyclones.
Mid-latitude or polar front jet stream
• It is more variable and is produced by a temperature difference
• In summers its position shifts towards poles and in winters towards equator
• Western Disturbances are the Temperate cyclones or extra-tropical storm originating in the Mediterranean
• Brings sudden winter rain and snow to the northwestern parts of the Indian subcontinent
• This is a non-monsoonal precipitation pattern driven by the Westerlies
• The moisture in these storms usually originates over the Mediterranean Sea and the Atlantic Ocean
• They travel from place to place due to difference in pressure. There is high pressure in northwestern Indian subcontinent favouring its travel
• During winters, low pressure system originates over the Mediterranean Sea & western Asia and moves into India, along with westerly flow.
• Western Disturbances are important to the development of the Rabi crop in the northern subcontinent, esp. wheat
• They shower rain over Pakistan, India and Nepal
• Extra-tropical storms are a global, rather than a localized, phenomena with moisture usually carried in the upper atmosphere (unlike tropical storms where it is carried in the lower atmosphere)
Winter Rainfall occurs due to:
• North East Monsoon
• Western Disturbances
• Tropical Cyclones
• A curious see-saw pattern of meteorological changes has been observed b/w Indian Ocean & Pacific ocean
• Whenever pressure is higher over Indian Ocean, low pressure prevails over Pacific Ocean & vice versa
• Scales used for this pattern is SOI (Southern Oscillation Index) – (Tahiti – Darwin) Pressure
Tahiti = Pacific Ocean, Darwin = Indian Ocean
• When SOI > 0 – Good monsoon in India – La Nina Condition
• When SOI < 0 – Bad monsoon in India – El Nino Condition
Before understanding El Nino & La Nina one must understand Walkar Cell & Ocean Circulations
Normal Year – Walker cell Condition at south Pacific
• LP – Northern Australia and HP – South America (Peru)
• South equatorial current pile up water at northern Australia – increase SST – called West Pacific Pool
• It brings rainfall in Northern Australia
• The diverging air above Australia move towards Peruvian coast
• They descend at Peruvian coast = HP – desiccating effect to Atacama desert
• Completes the Walker cell
• As south equatorial current take water from east to west
• It led water from bottom to come up and take the space
• Up-welling at the Peruvian coast = rich fishing ground
• Direction of walker cell reverses
• South equatorial current weakens (reason unknown) & strong counter current activates
• Weak piling up of water at Northern Australia
• Weakening of west Pacific Pool
• Ocean water move towards Peruvian coast
• Create LP system over there and rainfall at Atacama Desert
• The rising and diverging wind above Peru descends over Australia = HP condition – drought in Northern Australia
• The reversal in wind direction alters submarine cycle as well
• Down-welling at Peruvian coast – loss in fishing business
• It is a warm current which appears off the coast of Peru in December (3 – 36* S of Equator), also known as child Christ as it appears around Christmas
• It is temporary replacement of cold Peruvian / Humbolt current which normally flows against the coast & appears once in 3 – 7 years
• Responsible for widespread flood & droughts in various tropical regions of the world
• Warming of tropical pacific water affects the global pattern of pressure & wind system, including monsoon winds in Indian Ocean
• High pressure of Indian Ocean & low pressure at said area of Pacific Ocean shifts some of the monsoon winds to Pacific Ocean side which results in scarcity of rainfall in India
• Bring drought condition in Indonesia as well – forest fire
La Nina (The Girl in Spanish)
• After El Nino when weather conditions return to normal, trade winds become strong
• Hence they cause abnormal accumulation of cold water in central & eastern pacific region
• This creates a high pressure region in Pacific Ocean as compared to Indian Ocean
• Heavy rainfall – flood condition in Northern Australia – good monsoon in India
• Very good fishing business at Peruvian coast – price crash
• Drought in Atacama
• La Nina brings heavy monsoon showers in India due to N – E monsoon along with monsoon laiden pacific winds from tropical Pacific Ocean although it marks an active hurricane season at Peru
Impact of El Niño and La Nina on Indian Weather
• El Nino and La Nina are among the most powerful phenomenon on the Earth.
• These are known to alter climate across more than half the planet and dramatically impact weather patterns.
• Over Indian subcontinent, El Nino during winter results in development of warm conditions. During summer, it leads to dry conditions and deficient monsoon.
• It also leads to drought in Australia. On the other hand, La Nina results in better than normal monsoon in India. At the same time, in Australia it has caused floods.
• In the recent past, India experienced deficient rainfall during El Nino years 2002 and 2009 whereas monsoon was normal during El Nino years 1994 and 1997.
• This so far implies that in about 50 per cent of the years with El Nino during summer, India experienced droughts during monsoon. This implies that El Nino is not the only factor that affects monsoon in India.
• There are other factors that affect India’s rainfall pattern. These include North Atlantic SST, Equatorial SE Indian Ocean SST, East Asia Mean Sea Level Pressure, North Atlantic Mean Sea Level Pressure and North Central Pacific wind at 1.5 km above sea level.
SOME BASIC TERMINOLOGY RELATED TO PRE-MONSOON
DISTRIBUTION OF RAINFALL IN INDIA
• The rainfall in India is seasonal, uncertain and unevenly distributed
• Mainly pours down during the South-West Monsoon period
• On the basis of the quantity of rainfall, we can divide India into five major rainfall regions viz.
TROPICAL CYCLONES IN INDIA
• Increase in sea surface temperature of Bay of Bengal and Arabian Sea in Late summer
• Hence Possibility of Tropical cyclone
• Retreating SW monsoon branch drag them towards Eastern coast
• Tropical cyclones move from east to West
• They are secondary circulations and maintain the larger direction of the planetary winds (i.e. Trade winds which blow from East to West).
• So, any cyclones to form in Arabian sea is less likely to affect India
• But the Delta region of eastern coast is frequently struck by cyclone
HIMALAYAN SYSTEM AND ITS CLIMATE
India is separated from rest of the Asia by the wall of Himalayan mountain ranges. It restricts the cold and dry winds of Central Asia to the North of Himalayas. These mountain ranges also act as an effective physical barrier for rain bearing southwest monsoon winds and force them to shed their moisture within the country. Thus, it acts as an effective climatic divide between the Indian subcontinent and the central Asia.
Within the Himalayas, Climate varies depending upon elevation and location. Climate ranges from subtropical in the southern foothills to warm temperate conditions in the middle Himalayas to cold temperate conditions in the higher parts of middle Himalayas to a cold alpine climate at higher elevations.
• The temperature in the winter season falls progressively with the increase in altitude from sea level.
• At the foothill, the temperature in winter is about 18°C in the day time, at the middle Himalayas it is about 6 to 12°C and above this, the temperature is below freezing point.
• The higher elevations above 5000 meter are permafrost and Tundra type of climate. Dras valley in Kashmir is the coldest place in India. The minimum temperature recorded here on 28th Dec 1908 was -45°C.
• The frequency of western disturbances varies from year to year but on an average 3 to 5 disturbances per month are experienced.
• The average precipitation during the three months of winter season. i.e. from December to February is about 60cm in the Himalayan region.
• The eastern Himalayan region also gets rainfall from the north east monsoon. Although it is not so significant as the north east monsoon winds are coming from land and do not have sufficient moisture content due to lack of source, but the combined effect of western disturbances and north east monsoon causes an average precipitation of about 50 cm in Sikkim, Arunachal Pradesh and Assam.
• The period from March to June in India is the summer season. This season is mostly dry and hot. At the foothills of Himalayas, the maximum average temperature is about 30°C. Due to the effect of the lapse rate (6-5°C per 1000m of elevation) with altitude, the maximum temperature in the middle Himalayas ranges from 15°C to 25°C, varying in accordance with the altitude, latitude, and other governing factors of temperature.
• Above the elevation of 5000 m, the temperature is almost below freezing point throughout the year.
• The diurnal temperature range gradually reduces and is in the range of 11°C to 16°C varying with altitude, distance from sea, wind direction and other governing factors.
• This season is also called as monsoon season as it starts with the onset of northwest monsoon in India.
• The monsoon season in India generally starts in last week of May and first week of June varying year to year. The weather conditions change.
• The relative humidity of the atmosphere increases, sky is over cast with clouds, atmospheric temperature increases before the outbreak of monsoon and there may be some spells of pre monsoon showers.
• As the monsoon comes, there is significant fall in the atmospheric temperature ranging from 3°C to 6°C lower than the month of June in the Himalayan region.
• The night temperature is more or less constant while the day temperature fluctuates on day to day basis. The diurnal temperature range is less and varies between 4°C to 6°C due to the greenhouse effect created by the clouds.
• The eastern Himalayas get the monsoonal rain earlier than the western Himalayas due to nearness to the sea and the direction of movement of the Bay of Bengal branch of monsoon wind. Around June 5, the monsoon breaks in eastern Himalayas.
• However the Arabian Sea branch brings more precipitation due to its shorter length of journey uptill western Himalayas. Heavy rainfall is caused in the eastern Himalayas, sub Himalayan regions and the southern slopes of Himalayas. This leads to high flooding of the rivers having their catchment areas in Himalayas.
• For eg – Brahmaputra receives the water of the eastern Himalayas causing floods in the Assam plains, Kosi river receives the water of eastern Nepal Himalayas by Saptakosi catchment area causing floods in Bihar plains, etc.
• The western Himalayan region receives around 65 cm of average rainfall in the monsoon season, while the eastern Himalayas, as explained earlier, experience the precipitation around 200 cm to 410 cm on an average, while on some places, it reaches to as high as 600 cm also.
• In the Himalayan region, the monsoon in the western Himalayas reaches the last i.e. in the first week of July and withdraws from there first i.e. in the second week of September, which gives only two and a half month for the monsoonal activity in the western Himalayas.
• While in the eastern Himalayan region the monsoon strikes in the first week of June and withdraws in second week of October giving a period of four and a quarter of month for monsoonal activity.
• In the season with the cession of the monsoon initially the temperature rises in the range of 3°C to 5°C but within a week or two, the temperature starts falling steeply. Within a month and half i.e. from second week of December, the minimum temperature in the Himalayan region falls below the freezing point.
• The diurnal temperature range increases steeply due to lack of clouds and absorption of latent heat of melting by the ice sheets.
• During this season from the last week of October the western disturbances start to appear and their frequency increase on the monthly basis as the westerly jet stream gets stronger progressively with the southward movement of Sun and the ITCZ. These western disturbances bring snow fall in the upper reaches.
• This season draws huge amount of tourists in the Himalayan region because of the snow cover. It provides them a perfect place for the skiing and other winter sports.
• The areas receiving an annual rainfall of 200 cm and above are termed as areas of very high rainfall. The eastern Himalayas receive an annual rainfall of about 200 cm to 400 cm and even up to 400 to 800 cm in few pockets.
• Almost the whole of Arunachal Pradesh, Sikkim, Assam & Nagaland come under the area of heavy rainfall.
• The areas receiving a rainfall of 100cm to 200cm annually come under the zone of high rainfall. The southern parts of Jammu and Kashmir, Himachal Pradesh and Uttarakhand in Western Himalayas and other regions on the southern slopes of western Himalayas come under the zone of high rainfall.
• The areas receiving 50 cm to 100 cm of rainfall comes under the region of low rainfall. The leeward side of the southern Himalayas in Jammu and Kashmir and the valley areas of western Himalayas come under the zone of low rainfall.
• The areas receiving a rainfall of less than 50 cm comes under the zone of very low rainfall.
• The only area which is receiving less than 50 cm of rainfall in the Himalayan region is the Ladakh region of the state of Jammu and Kashmir.
• This area does not have the temperature as high as that of tropical and subtropical region that is why Ladakh region is also called as cold desert.
CLIMATE OF THE GREAT NORTHERN PLAIN:
The cold weather season or winter season:
• From November to March there is cold weather season, clear sky, low temperature and humidity, high range of temperature, cool and humidity, high range of temperature.
• Cool and slow northern winds are the chief characteristics of this season.
• The coldest month in the Gangetic plains is January and temperature ranges from 12.5°C to 17.5°C. The minimum temperature even goes upto 5°C.
The Summer Season:
• The summer season is from March to June. High temperature and low humidity are the chief characteristics of this season.
• It is also known as hot weather season or hot dry summer season. In this season, there is a progressive northward march of warmth as the sun proceeds towards the north.
• In June, north India has much higher temperature. In May the highest temperature in Rajasthan may be as high as 48°C and in June the same condition is in Punjab and Haryana.
• The highest temperature recorded so far is 50-60°C at Ganganagar. The highest temperatures are recorded just before the onset of monsoon.
• The minimum temperature at night rarely falls below 20°C to 25°C and the diurnal temperature range is also very high.
The Rainy Season:
• There is a significant fall in temperature with the start of arrival season. In the north-west, the temperature falls by 2°C-3°C. After this fall in temperature, it remains more or less uniform throughout the rainy season.
• There is a rise in temperature whenever there is break in the monsoon. Night temperature is more uniform than the day temperature. The diurnal range of temperature is also small due to clouds and rains, which ranges between 4°C to 8°C.
• The highest temperature of over 32°C are experienced in Thar desert of Rajasthan. This is due to lack of clouds and the predominance of continental airmass. In general the Great Plains have temperature above 30°C.
• Low pressure condition still prevails due to high temperature. There is an elongated trough across the Ganga basin right upto the head of Bay of Bengal, known as monsoon trough. The atmospheric pressure in most parts of the north India is less than 1000mb.
The cool Season:
• This season starts with the bringing of the withdrawal of the South West monsoon, in the middle of September and continues upto November after which winter starts.
• It withdraws from the Northwest end first. The south west monsoon reaches the northwest end of plains last and withdraws from there first of all. Here the duration of monsoon is minimum.
• The clouds disappear and the sky becomes clear. The day temperature rises a little at the initial stage but soon starts falling rather steeply. The diurnal temperature range is between 10 to 16°C and the night temperature is very low.
• The elongated trough of the low pressure across the Indo-Gangetic plains weakens and gradually shifts south ward. The axis of low pressure roughly runs in an east-west direction along 13°N latitude.
• North Western Region : It includes northern parts of Punjab. The winter and summer temperature are 16°C and 24°C.
• The Arid Land : This is a vast dry area which includes the Thar desert of Rajasthan and South West of Haryana. The average temperature in winter varies from 16°C to 24°C which shoots up to 48°C in summer. Jaipur is its representative city. The average annual rainfall does not exceeds 40 cm.
• The region of moderate rainfall : Parts of Punjab, Haryana, Western, Uttar Pradesh, NCR of Delhi and eastern Rajasthan are areas of average rainfall with an annual rainfall of 40 to 80 cm. Temperature in January is 15 to 18°C while in July it is 33 to 35°C. Most of the rainfall occurs in summer. Delhi represents this region.
• The Transitional Zone : Eastern Uttar Pradesh and Bihar comprise the transitional zone between areas of average rainfall on the west and areas of heavy rainfall in the east. The average annual rainfall in this region is 100-150cm. The temperature in January is between 15°C to 19°C while in July it is 30°C to 35°C. Patna is the representative city.
• Region of Very heavy and heavy rainfall : This region which receives very heavy rainfall which is more than 200 cm of rainfall. The temperature remains around 18°lC in January and between 32°C to 35°C in July. West Bengal is the state which receives heavy rainfall. The rainfall is between 100 to 200cm. The temperature in January ranges between 18°C to 24°C while in July it is 28°C to 35°C.
THE PENINSULAR PLATEAU AND ITS CLIMATE:
Factors Influencing the Climate of Peninsular India:
• Water bodies comprising the Arabian Sea and the Bay of Bengal surround the peninsular India and make the climatic condition mild along the coastal areas.
• Areas near the coast have equable or marine climate.
• The south-west monsoon winds strike the Western Ghats and cause heavy rainfall on the windward side while the leeward side is rain shadow zone.
• The most dominant factor of the climate of this region are Monsoon and ENSO oscillation.
• Tropical cyclones originate in the Bay of Bengal and Arabian Sea and they influence large part of the peninsular India.
The Cold Weather Season or Winter Season:
• The southern peninsula has rather warm condition and does not have distinctly defined winter weather.
• The isotherm of 200C runs in east-west direction roughly parallel to the tropic of cancer and divides India climatically in the northern and southern parts.
• In the peninsula temperatures are invariably above 200C. In the extreme south the temperature may be well above 250C.
• The pressure is comparatively lower in south India. The isobar of 1013mb touches the southern tip of India.
• The wind starts blowing in the direction of north west to south east. However the wind velocity is low due to low pressure gradient.
• The retreating winter monsoon picks moisture while crossing Bay of Bengal and cause Winter rainfall in Tamil Nadu and south Andhra Pradesh, south east Karnataka and south- east Kerala.
• The highest seasonal rainfall of about 75cm between October and December occurs along the south- eastern coast of Tamil Nadu and adjoins parts of south Andhra Pradesh.
The Summer Season:
• The period from March to June is called the summer season. Sometimes also referred to as pre- monsoon period as the season advances, sun’s vertical rays move northwards and large parts of the country including south of Satpura range are heated up.
• The southern parts are distinctly warmer in March and April. In March, the highest temperatures are nearly 400C in the southern parts of the Deccan plateau.
• Even the night temperature ranges between 200Cto 250C and even 270C in the Deccan region.
• However, the maximum summer temperatures are comparatively lower in the southern parts of the country due to moderating effect of sea.
• The mean maximum temperature at most places is about 260C to 300C.
• The temperatures along the West coast are comparatively lower than those prevailing on the east coast due to prevailing westerly winds.
• Coastal areas of Kerala and Karnataka receive about 25 cm of rainfall from thunderstorms. These thunderstorms also cause about 10cm of rainfall in the interior of south India.
• In Tamilnadu and Andhra Pradesh they are very beneficial to mango crop. In Karnataka they are called cherry blossoms due to their salutary effects on the coffee plantation.
• The June temperature in south India is 30 to 60C lower than the May temperature.
• The temperatures are quite low over the Western Ghats due to high elevation and also due to heavy rainfall, but the rain shadow area is comparatively warmer on account of low elevation and scanty rainfall.
• The coastal areas of Tamil Nadu and adjoining parts of Andhra Pradesh have temperatures above 300C because they receive little rainfall during this season.
The cool season:
• The monsoons withdraws from the peninsula by October and from the extreme South Eastern tip by December. Due to retreat of the monsoon, this season is also called as the Season of retreating monsoon.
• Unlike the sudden burst of the advancing monsoons, the withdrawal is rather gradual and takes about three months. The temperature decreases to 330C in the peninsular and to 300C in the Meghalaya Plateau.
• October and November is the main rainy season in Tamil Nadu and adjoining areas of Andhra Pradesh to the south of Krishna river delta as well as secondary rainy period for Kerala. The retreating monsoon absorbs moisture while passing over the Bay of Bengal and causes this rainfall.
The areas receiving very high rainfall (above 200cm) include the West coast from Thiruvananthapuram to Mumbai. The average annual rainfall in this area is 100 to 400 cm. With isolated pockets receiving above 400cm, Meghalaya is the wettest part of the country with Mawsynram getting 1221 cm is highest in the country.
The areas receiving high rainfall (100 to 200 cm) include eastern slopes of the Western Ghats, Madhya Pradesh, Andhra Pradesh and Tamil Nadu. The areas receiving low rainfall (50 to 100 cm) include large parts of Gujarat, Maharashtra, Western Madhya Pradesh, Andhra Pradesh and Karnataka.
Climatic Regions of Peninsular India:
• Region of Very Heavy Rainfall: It receives more than 200cm of rainfall and include large parts of Meghalaya. Temperature remains around 180C in January and rise to 320C to 350Cin July.
• Region of Heavy Rainfall: Chhattisgarh, Jharkhand, Orissa and Northern Andhra Pradesh receive 100-200cm annual rainfall and are termed as areas of heavy rainfall. The rainfall is primarily rough by winds coming from Bay of Bengal. The amount of rainfall decreases from east to west. The January and July temperature ranges from 180C to 240C and 290C to 350C respectively.
• Region of Moderate Rainfall: It includes the areas between Western and Eastern Ghats which receive annual rainfall of 50 to 100 cm. The rainfall is comparatively low. The January and July temperature ranges between 180 to 240C.
• The Kankan Coast: Extending from Mumbai in the north to Goa in the south, the Kankan coast receives over 200 cm annual rainfalls brought by Arabian Sea branch. The temperatures remains fairly high and vary from 240C to 270C. The annual range of temperature varies around 300C.
• The Malabar Coast: It extends from Goa to Kanyakumari and receives heavy rainfall of over 250cm. The rainfall is mainly brought by South West monsoon winds, which continues for about 9 months the temperature remains in the vicinity of 270C, and the annual average range of temperature is 300C.
• Tamil Nadu: It includes Tamil Nadu and adjoining areas of Andhra Pradesh. The rainfall varies between 100 to 150 cm and mainly caused by retreating monsoon from North east. During November and December, the temperature remains around 240C with annual range of 300C.