PHYSIOGRAPHY OF TAMIL NADU

• Tamil Nadu has unique physiography.
• To the west and the northwest, it is bounded by hills of both western and Eastern Ghats.
• In the east, it is bounded by the Bay of Bengal and in the south by the Indian Ocean.
• The physiography of Tamil Nadu is a high land which has uneroded, the Western Ghats on the west and low lying coastal and river plains on the east.

Physiography of Tamil Nadu

Geographically Tamil Nadu may be divided into four physical divisions

• The Hilly region (the Western Ghats and the Eastern Ghats).
• The Plateau
• The Plain
• The Coastline

The hilly regions of Tamil Nadu

• The Western Ghats enters the state through the Nilgiris District and runs up to Kanyakumari district.
• The Western hilly region is much more complex than the Eastern Ghats.
• Its average height is from 1000 m to 1500 m.
• The Western Ghats has mountain peaks namely Doddabetaa (2637 m) and Mukuruthi (2540 m).
• In the north-west of Western Gats lies the Nilgiri highland region at a height of above 2500 m.
• In this region, there are few peaks found at a height ranging from 1800 m to 2400 m.
• The highest peak of Tamil Nadu is Doddabetta.
• The Western Ghats and the Eastern Ghats meet at the Nilgiris hills.
• From the Nilgris of Tamil Nadu and Anaimalai hills of Kerala, an offshoot runs at a height of 1500 m to 2000 m in the east.
• To the south of the Palani hills, there are two other ranges namely, Varshanadu and Andipatti hills running parallel to the Cardamom hills.
• Though the Western Ghats is a continuous range it has a gap of 25 km at Palghat.
• To the south of Palghat, gap hills such as Andipatti, Elamalai and Agathiya Malai are found.
• Kambam valley is between Thekkadi hills Varshanadu hills and Kodaikanal hills.
• This valley is considered as the green valley of Tamil Nadu.
• The gap in between Varshanadu hills and Agathiya malai is called the Shenkottai pass.
• The Tamil Nadu hills separating the plains and the plateaus have two well market passes namely the Attur pass in the south and the Chengam pass in the north.
• This pass links the Cuddalore and Villupuram district in the plain with the Salem district on the plateau.
• The Palakkad gap and Shencottah gap are the only breaks in the long chain of hills that border Tamil Nadu on the west.
• The Eastern Ghats are not continuous when compared to the Western Ghats.
• They are dissected into isolated hill ranges extending from northeast to southwest through the districts of Vellore, Dharmapuri and Erode.
• The average elevation ranges from 1100 m to 1600 m. these hillocks are called by different names in different areas, such as
• Javadi Hills and Elagiri Hills in Vellore District
• Shervarayan in Salem District
• Kalvarayan in Villupuram District
• Pachaimalai in Thiruchirapalli District
• Kolli hills in Namakkal District
• Chitteri hills are in both Dharmapuri and Salem District
• Gingee hills in Thiruvannamalai District
• The highest hills of Eastern Ghats – Shervarayan (1,500 – 1,600 m).
• The highest hills of Western Ghats – Anaimalai (2,700m)

Plateaus of Tamil Nadu

• The Eastern and Western Ghats meet at the Nilgiris plateau.
• Four km from this plateau, it slopes gently downwards to about 1,800 m towards Coimbatore.
• It extends from the Nilgris to Dharmapuri plateau or Bramahal plateau and lies to the west of Shervaroy uplands.
• This plateau is found with extreme abruptness on all sides. The Bramahal Plateau in Dharmapuri district is at an elevation of 300 to 700 m which merges with the Mysore plateau in the west.
• The elevation of the plateau increases from the east (120 m) to the west (300 to 450 m). Plateaus of Tamil Nadu can be grouped into two as Coimbatore plateau and Madurai plateau.
• In between the plateaus, isolated hills are also seen
• One such isolated hill is Chennimalai of Erode district.

Plains of Tamil Nadu

• Plains of Tamil Nadu can be classified into two as coastal plains and rivers plains.
• The coastal plains of Tamil Nadu extend from Pulicat Lake in the north to Kanyakumari in the south to a length of 1,000 km at an average elevation of 50 mt.
• The notable beaches found here are the Marina beach and the Rameshwaram beach.

Marina Beach

• It is the second-largest beach in the world.
• Marina Beach extends up to a distance of 13 km and it is one of the major tourist attractions of Chennai.

Rameswaram Beach

• The beach of Rameswaram is famous for its beautiful coastal features.
• The sea waves rise to a maximum height of only 3 cm and the view looks like a very big river.
• The coastal plains of Thiruvallur, Kancheepuram, Cuddalore and Villupuram are together known as the Cholamandalam plains.
• The river plains in Tamil Nadu are formed by the rivers Palar, Cheyyar, Pannar and Velllarin the north; Kaveri and its tributaries in the central region, Vaigai, Vaippar and Thamiravaruni in the south.

Rivers of Tamil Nadu

• The Northern Rivers of Tamil Nadu are Araniyar, Korattalaiyar, Palar, Cheyyar, Kedilam, Manimuthar and Thenpennar.
• Among the rivers and Palar and Pennaiyar flow from headwaters of Kolar Plateau towards the east.
• Cheyyar and Agaram are two tributaries of Palar.
• The main river of the state is Kaveri which originates in Kodagu district of Karnataka.
• Kaveri and its tributaries in its lower course drain the districts of Nagapattinam, Thanjavur, Thiruvarur and Thirucharapalli.
• The Kaveri, the kollidam and the velar jointly drain central part of the Tamil Nadu.
• The head of the Kaveri delta is near the island of Srirangam.
• Kollidam branches off from Kaveri at Grand Anaicut (Kallanai).
• In the Kaveri delta, the distributaries such as
• kollidam
• Manniyar
• Vennar
• Vettar
• Arasalar
• Nattar
• Mudikondinar
• Kudamuruti
• Veera cholanar have formed an alluvial plain in a quadrangle shape.
• Kaveri along with its tributaries Bhavani, Noyyal, Moyar and Amaravathi, is the most important source of canal irrigation.
• Towards the south of Tamilnadu, there are few rivers like Vaigai (Madurai), Vaippar (Virudhunagar), Tamirabarani (Thirunelveli), Gundar (Thooothukudi, Ramanathapuram), Chittar (Thirunelveli) and Kothaiyar (Kanyakumari).
• Most of the soils of the plains of Tamil Nadu are alluvial, formed by these rivers flowing east.
• In the southwest of Tamil Nadu is the Suruliyar River that drains a part of Madurai district.

The climate of Tamil Nadu

• Physiography nearness to the sea and geographical location determine the overall climatic conditions of any region.
• Climate refers to the sum total of weather conditions and variations over a large area in a long period of time (more than thirty years).
• Weather refers to the state of the atmosphere over an area at any particular point of time.
• The major climatic elements are
• Temperature
• Pressure
• Wind
• Humidity
• Clouds
• Precipitation
• Tamil Nadu has a tropical climate.
• Two factors namely, the apparent position of the Sun and the monsoonal rain-bearing winds influence the climatic conditions of Tamil Nadu.
• The vertical rays of the sun fall on the State twice in a year.
• Though Tamil Nadu lies in the tropical region, the local weather conditions such as temperature humidity, clouds and wind directions along with wind speed, change the climatic conditions to a greater extent.
• This is this region of climatic variation that exhibits the influence of the coastal and the interior inland locations.
• The temperature of the state starts increasing in the second week of February and gradually increases in the months of March to June.
• The hottest part of the summer season is known as Agni Nakshatram (star of Fire) or Kathiri veyyil.
• The decrease in temperature is from the second week of June to the first week of October.
• The month of October is the season for the retreating or northeast monsoon.
• From then on, the temperature starts to decrease up to the month of February.
• In Tamil Nadu, May is the hottest and January is the coldest month.
• Though this is the general situation the overall climatic condition varies among mountainous regions, plateaus, coastal and interior plains.

The following table explains it clearly.

S. No.	Geographical Locations	Weather recording stations	Temperature in Celsius
			Summer season	Winter season	Rainy Season
1	Coastal regions	Chennai	40oc	22oc	25oc
2	Interior Plains	Vellore	42oc	21oc	22oc
3	Inland regions	Thiruchirappalli	42oc	20oc	23oc
4	Hilly regions	Kodaikanal	11oc	6oc	14oc
5	Plateau	Coimbatore	32oc	26oc	21oc

• The relative humidity in the state is found to be high in winter season than in summer season.
• The average humidity of the air is about 68% in the month of May whereas it is 82% in January.
• The rate of evaporation is more during the summer season than in the winter season.
• The state possesses thick rain-bearing clouds in the months of October, November and December.
• The rainy seasons of the state may be grouped into three
• South West Monsoon
• North-East Monsoon
• Cyclonic Rainfall

South-West Monsoon

• The South-West monsoon occurs between June and September.
• The districts that are benefitted by this season are the Nilgiris, Kanyakumari, western parts of Coimbatore, Dharmapuri and Salem.
• As the South – West monsoon starts downpour of rain in the Western Ghats, the western parts of Tamil Nadu receive about 150 cm of rainfall on an average.
• Most of the Eastern and Central part of Tamil Nadu becomes rain shadow region for this season.
• The occurs due to the south-westerly direction of monsoonal winds in this season.
• In general, the amount of rainfall of south-west monsoon decreases from west to east.
• The Nilgiris district receives about 70% of its annual rainfall followed by the Salem and Erode districts.
• More during the summer season than in the winter season.
• The state possesses thick rain-bearing clouds in the months of October, November and December.

Major Seasons of Tamil Nadu

Seasons	Tamil Name	Tamil Month
Summer (April to August)	Illavenil, Muduvenil	Chitirai, Vaikasi,   Aani, Aadi
Rainy (August to December)	Khar Season, Khulir	Avani, Puratasi, Iypasi, Karthigai
Winter (December to April)	MunPani, Pin Pani	Markhzhi, Thai, Masi and Panguni

• The word monsoon is derived from the Arabic word ‘mausim’ which literally means season. Monsoon refers to the seasonal reversal in the wind direction between seasons.

Northeast Monsoon

• The Northeast Monsoon season occurs between October and December.
• The coastal and interior plains of Tamil Nadu are highly benefitted by this rainy season.
• Normally northeast monsoonal rain is highly associated with the cyclonic formation.
• In this season the amount of rainfall decreases from east to west.
• Excepting Kanyakumari, all other interiors south and western parts of Tamil Nadu receive lesser rainfall coastal districts such as
• Chennai
• Cuddalore
• Thiruvallur
• Kancheepuram
• Villupuram
• Nagapattinam
• Thiruvarur
• Tirunelveli districts receive about 150 to 250 cm of rainfall.
• Tiruchirappalli Salem and Erode receive about 100 to 150 cm of rainfall.
• Cyclonic Rainfall
• November is the month of cyclonic rainfall.
• The low-pressure formations in the southern part of the Bay of Bengal intensify the Cyclonic rainfall along with the coastal districts of Tamil Nadu.
• An equal portion of rainfall is received from both the Northeast Monsoon and the Cyclonic rainfall in the coastal districts of Tamil Nadu.
• On the basis of annual rainfall received the districts of Tamil Nadu can be grouped into 5 rainfall regions.
• It is clear that the coastal districts along with Nilgiris fall under the very heavy rainfall region with an annual rainfall of more than 1400 mm.
• Among the districts, Kanyakumari is fortunate enough to receive rain from all the rainy seasons.
• Very low amount of annual rainfall is received by the Coimbatore and Tiruppur districts.

Season wise percentage of annual rainfall

Seasons	Annual Rainfall (%)
South West Monsoon	22
North-East Monsoon	57
Cyclonic Rainfall	21

Rainfall Regions of Tamil Nadu Distribution of rainfall (2007 – 2008)

Distribution of Rainfall	Amount of Rainfall	Districts
Very Low Rainfall	Below 800 mm	Coimbatore, Tiruppur
Low Rainfall	From 800 mm to 1000 mm	Namakkal, Karur, Thuthukudi, Erode, Dharmapuri, Madurai, Thiruchirappalli, Perambalur, Krishnagiri.
Moderate rainfall	From 1000 mm to 1200 mm	Pudukkottai, Virudhunagar, Sivagangai, Thanjavur, Salem, Ramanathapuram, Dindigul, Theni, Vellore.
High rainfall	From 1200 mm to 1400 mm	Thirunelveli, Thiruvannamalai, Kanyakumari
Very High rainfall	Above 1400 mm	Kancheepuram, Chennai, Villupuram, Thiruvallur, Thiruvarur, Cuddalore, Nagapattinam, Nilgiris

 

Natural Vegetation

• Vegetation that grows naturally without the effort of the human being is called Natural vegetation.
• Its growth depends upon the temperature, rainfall and type of soils.
• According to the National Forest Policy, a region should have 33% if its land under forest.
• Unfortunately, Tamil Nadu has only 17% of its land under forest.
• In the state, forests are confined to the Western Ghats and the Hilly regions.
• Among the districts, the Nilgiris possesses the highest percentage of area under forest followed by Theni, Dharmapuri and Kanyakumari districts.
• In the coastal regions, the dry weather and poor soil allow only casuarina tree to grow.
• Heavy rainfall regions show the prominence of tropical evergreen forests.
• Javadi Hills are noted for their fruit-bearing trees and sandalwood.

Distribution of Forests

• The distribution of forests among different districts of the state is very uneven.
• The concentration of forests is mostly on the hills of the western districts and in the Javadi group of hills in Vellore district.
• Dense forests are also seen in Salem district.
• More than half of the area in the Nilgiris is under forests.
• Other districts hold 1 to 5% if the area under forests.
• Thanjavur being the alluvial plain is suitable for agriculture which has less than 1% of forest cover.
• The forests of Tamil Nadu have different types of trees. Most of the trees in the state shed their leaves in the dry season.
• Tamil Nadu has large areas of sandalwood plantations, about 5,88,000 hectares.
• Hardwood trees are available in the forests of Coimbatore, Nilgiris and Kanyakumari.
• Trees that are used as fuel are found in Madurai, Coimbatore and Thirunelveli districts.
• Kanyakumari district has rubber plantations.
• In the Nilgiris, camphor and eucalyptus trees are grown under afforestation.
• In the foothills of the Western Ghats and parts of Thirunelveli and Virudhunagar districts, there are trees that are used for making matchsticks.
• The trees such as peepal, blue apples, jack fruit and gooseberries grow all over the state.

Types of Forests

Natural Vegetation can be broadly divided into five different types.

• Tropical evergreen forests
• Tropical deciduous forests
• Thorny shrub forests
• Mangrove forests
• Hill forests

Tropical evergreen forests

• As the name implies these forests are evergreen and they never shed their leaves in a particular season.
• Since the leaves are present always they are called as the evergreen forests.
• Tropical evergreen forests are distributed in the regions of heavy rainfall (above 200 cm annual rainfall).
• These forests are found along the slopes of the Nilgris and Anamalai hills and the coastal areas of Tamil Nadu.
• The hardwood trees like ebony, teak, rosewood and ironwood are also funded here.
• They grow to a height of 60 m.

Tropical deciduous forests

• These forests are found in the areas having rainfall ranging between 100 and 200 cm per year.
• They are found on the eastern slopes of the Western Ghats.
• These are also called as monsoon forests. The trees of these forests shed their leaves to avoid the loss of moisture during the dry season.
• Trees of different varieties such as tall and short, soft and hardwoods are found in these forests.
• Some of them are sal, sandal, woo, teak, bamboo and paddock.

Thorny shrub forests

• Thorny shrub forests are found in the areas where there are long dry periods and low rainfall.
• This type of vegetation includes low, widely scattered low trees and bushes.
• They are highly adaptive to dry conditions, with deep roots, thick stems and fleshy leaves.

Mangrove forests

• Mangroves are found in the tropical and subtropical tidal areas which have a high degree of salinity.
• Mangrove trees grow along the estuaries and backwaters.
• In Tamil Nadu Pitchavarm, Kodikkarai and Vedaranyam, have mangrove or tidal forests.
• Pitchavaram has the largest swam forest cover in the state.
• It is near the city of Chidambaram in Cuddalore district submerged under the backwaters of the Bay of Bengal.
• Here thicky wooded islands of mangroves are found covering an area of about 1,214 hectares.
• These forests also contain tropical evergreen trees and shrubs belonging to the genus Rhizophora.
• In Pitchavarm mangrove forests are found in 25 km2and Kodikkarai the forests cover about 17 km2

Hill forests

• These forests are found along the hill slopes where the rainfall is heavy.
• In the hills of Anamalai and Nilgiris, different varieties of flora such as trees, shrubs, climbers and creepers are found according to altitude.

Forests Product

• The forest products of Tamil Nadu may be divided into two: major and minor products.
• Major products include timber and fuelwood.
• Timber is used for many purposes namely:
• Building construction
• Making for furniture
• Boat building
• Plywood
• Hardwood
• Matches
• Pulp
• Paper industries
• Packing boxes
• Wooden toys
• Pencils
• Wood carving

The minor products are

• bamboo, canes, leaves, greases essential oils, medicinal plants, and resins, gums, tanning materials, spices, dyes, beeswax, honey, turpentine and lac.
• A large number of these products are used as raw materials for cottage industries while some serve as valuable articles of export.