Climate of Tamil Nadu Notes
Tamilnadu Notes in English Part 3
3. Climate of Tamil Nadu
Physiography, nearness to sea and geographical location determine the overall climatic conditions of any region.
|Weather refers to the state of the atmosphere over an area at any particular point of time.
Climate refers to the average weather conditions and variations over a large area in a long period of time (more than thirty years).
The major climatic elements are: temperature, pressure, wind, humidity, clouds and precipitation.
Tamil Nadu has 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 direction along with the wind speed, change the climatic conditions to a greater extent. This is the region of climatic variation that exhibits the influence of the coastal and the interior 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 decreases of 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, 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.
Table: Region-wise seasonal average temperature
|S.No||Geographical Locations||Weather recording stations||Temperature in Celsius|
|Summer season||Winter season||Rainy season|
The relative humidity in the state is found to be higher in winter when compared to summer. 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 higher during the summer than in the winter the state possesses thick rain bearing clouds in the months of October, November and December.
Table: Major Seasons of Tamil Nadu
|Seasons||Tamil Name||Tamil Month|
|Summer (April to August)||Illavenil
|Rainy (August to December)||Khar season
|Winter (December to April)||Mun Pani
Masi and panguni
The rainy seasons of the state may be grouped into three
1) South West Monsoon
2) North East Monsoon
3) Cyclonic Rainfall
The southwest monsoon occurs between June and September. The districts that are benefitted by this season are the Niligris, Kanyakumari, western parts of Coimbatore, Dharmapuri and Salem. As the South-west monsoon starts its downpour of ain 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 parts of Tamil Nadu become rainshadow region in this season. This occurs due to the south westerly direction. 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. Kanyakumari district also receives sufficient amount of rainfall from this season.
|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.|
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, the Northeast monsoon rain is associated with cyclonic formation. In this season, the amount of rainfall decreases from east to west. Except Kanyakumari, all other interior south and western parts of Tamil Nadu receive less rainfall. Coastal districts such as Chennai, Cuddalore, Thiruvallur, kancheepuram, Villupuram, Nagapattinam, Thiruvarur and Thirunelvelli districts receive about 150 to 250 cm of rainfall. Trichirapalli, Salem and erode receives about 100 to 150 cm of rainfall.
November is the month of cyclonic rainfall. The low pressure formations in the southern part of the Bay of Bengal intensifies and forms the cyclonic rainfall. An equal amount 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. From the table given below it is clear that the coastal districts along with Nilgris falls 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.
Table: Season wise percentage of annual rainfall
|South west Monsoon
North East Monsoon
Table: rainfall Regions of Tamil Nadu Distribution of rainfall (2007-2008)
|S.No||Distribution of Rainfall||Amount of Rainfall||District|
|1||Very low rainfall||Below 800mm||Coimbatore, Tiruppur.|
|2||Low rainfall||From 800 mm to 1000mm||Namakkal, Karur, Thuthukudi, Erode, Dharmapuri, Madurai, Thiruchirappalli, Perambalur, Krishnagiri.|
|3||Moderate rainfall||From 1000 mm to 1200mm||Pudukkottai, Viruthunagar, Sivagangai, Thanjavur, Salem, Ramanathapuram, Dindigul, Theni, Vellore.|
|4||High rainfall||From 1200 mm to 1400mm||Thirunelveli, Thiruvannamalai, Kanyakumari|
|5||Very High rainfall||Above 1400mm||Kancheepuram, Chennai,Villupuram, Thiruvallur, Thiruvarur, Cuddalore, Nagapattinam, Nilgiris.|
Cyclonic Track of Jal (6-8th, Nov 2010)
Tamil Nadu District-wise Annual Rainfall(2007-2008)
Vegetation that grows naturally without the effort of human beings 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% of its land under forest. Unfortunately, Tamil Nadu has only 17% of its land under forest. In the state, forest 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 allows only casuarinas tree to grow. Heavy rainfall regions show prominence of tropical evergreen forests. Javadi hills are noted for their fruit bearing trees and sandal wood.
Distribution of Forests
The distribution of forests among different districts of the state is very uneven. 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% of area under forests. Thanjavur being an alluvial plain is suitable for agriculture and it 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 sandal wood plantations, about 5,88,000 hactares. Hard wood trees are available in the forests of Coimbatore, Niligiris 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
The Natural Vegetation can be broadly divided into five different types.
- Tropical evergreen forests;
- Tropical deciduous forests;
- Thorny shrub forests;
- Mangrove forests and
- Hill forests.
Tropical evergreen forests
As the name implies forests are evergreen and they never shed their leaves in a particular season. Since the leaves are present always, they are known 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 hard wood trees like ebony, teak, rosewood and ironwood are also found here. They grow to a height of 60m.
Tropical deciduous forests
These forests are found in the area 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 dry season.
Trees of different varieties such as, tall and short, soft and hard woods are found in these forests. Some of them are sal, sandal wood, 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 trees and bushes. They are highly adaptive to dry conditions, with deep roots, thick stems and fleshy leaves.
Mangroves are found in the tropical and sub-tropical tidal areas, which have a high degree of salinity.
Mangrove trees grow along the estuaries and back waters. In Tamil Nadu, Pitchavaram, Kodikkarai and Vedaranyam, have mangrove or tidal forests. Pitchavaram has the largest swamp forest cover in the state. It is near the city of Chidambaram in Cuddalore district submerged under the back waters of the Bay of Bengal. Here, thicky wooded islands of mangroves are found covering an area of about 1214 hactares. These forests also contain tropical evergreen trees and shrubs, belonging to the genus Rhyzophora. In Pitchavaram mangrove forests are found in 25 km2 and Kodikkarai the forests cover about 17km2.
These forests are found along the hill slopes where the rainfall is heavy. In the hills of Anamalai and Niligris, different varieties of flora such as trees, shrubs, climbers and creepers are found, according to altitude.
The forest products of Tamil Nadu may be divided into two: major and minor products. Major products include timber and fuel wood. Timber is used for many purposes namely:
- Building construction;
- Making for furniture;
- Boat building;
- Hard wood;
- Paper industries;
- Packing boxes;
- Wooden toys;
- Pencils ; and
- Wood carving.
The minor products are bamboo canes, leaves, grasses, essential oils, medicinal plants, resins, gums, tanning materials, spices, dyes, beewax, 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.