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Climatic Regions of India According to Dr. Trewartha’s scheme

April 19, 2010

Dr Trewartha’s scheme has been most satisfactory of all classifications of the Indian climatic regions. He presented a modified form of Koppen’s classification. Dr. Trewartha’s classification divides India into four major regions of the A, B, C and H types. The A type refers to tropical rainy climate where high temperatures are consistent. The B type stands for a dry climate with high temperatures but little rainfall. The C type indicates a region with dry winters where low temperatures range between 0 °C and 18°C. The H type indicates a mountain climate. The A, B, and C types are further sub-divided.

There are seven climatic types.

Tropical Rain Forest (Am) Found in the westcoastal plains, the Sahyadris and parts of Assam, this climate is responsible for high temperatures that do not fall below 18.2°C even during winters. Temper tures rise to 29°C in April and May which are t] hottest months. Rainfall, though seasonal, is heav that is, about 200 cm annually during May-Nover ber.

Tropical Savanna (Aw) This climate is prevale in most of the peninsular areas except the semi-ar, zone in the leeside of the Western Ghats. It brinl the mean monthly temperature to above 18.2 c during the winters and to about 32°C in summer The maximum temperature may shoot up to 46 0 and sometimes even to 48°C. Rainfall is from Jur to September, although in the south, it may contim upto December end. Annual rainfall varies from ~ cm in the west to 152 cm in the east. As Tamil Nad has a more equitable temperature and experienc. more rainfall during October-December, it is class tied under the sub-type of Tamil Nadu Aw.

Tropical Semi-Arid Steppe Climate (BS) TI rainshadow belt runs southwards from centri Maharashtra to Tamil Nadu in the leeside of tt Western Ghats and the Cardamom Hills. It includE Karnataka state, the interior of Tamil Nadu, wester Andhra Pradesh and central Maharashtra. Temperc ture varies from 20°C to 23.8°C (December) an 32.8 °C (May) which are the coldest and hotte: months respectively. Annual rainfall is unreliabll varying from 40 to 75 em. So it is known as tl1 famine zone of India.

Tropical and Sub-Tropical Steppe (BSh) This climate is prevalent from Punjab to Kutch across the Thar desert and over northern Gujarat and western Rajasthan. Tem perature vades from 12°C Uanuary) to 35°C in June. January and June are the coldest and hottest months of the year I,”espectively. The maximum temperature rises up to 49°C. The annual rainfall, varying from 30.5 to 63.5 em, is also highly erratic.
Tropical Desert (BWh) This climate extends over the western parts of Barmer, Jaisalmer and Bikaner districts of Rajasthan and parts of Kutch. Mean monthly temperature is uniformly high (about 34.5 °c) throughout the region during May and June, the hottest months. During winters, temperature decreases towards north. The rainfall is scanty with an annual average of 30.5 em, with some parts receiving a low 12.7 em. Moreover, it is also very erratic. Rains are mostly in the form of cloud bursts, taking place mostly in July-September when the south-west monsoons may penetrate the region.

Humid Sub-Tropical Climate with Dry Winters (Caw) The climate. covers a large area to the south of the Himalayas, east of the tropical and sub-tropical steppe and north of the tropical savanna from Punj~b to Assam. It also extends into Rajasthan east of the Aravalli range. Winters are mild to severe. Summers are extremely hot in the western part but quite mild in the east. May-June are the hottest months. The annual rainfall in the area varies from 63.5 em to more than 254 em, most of it received during the south-west monsoon season. Rainfall is more towards the east and north where the atmosphere is humid. Winters are dry except for a little rain received from the westerly depressions.

Mountain Climate(H) Such type of climate is seen in mountainous regions which rise above 6,000 m or more such as the Himalayas. There is a sharp contrast between the temperatures of the sunny and shady slopes. Inversion of temperature and variability of rainfall are felt progres sively as one ascends to altitudes ~gher than 1,500 m.

The Trans-Himalayan belt situated to the northern side of the western Himalayas has a climate which is dry and cold. Vegetation is sparse and stunted. Winters are very cold and rainfall is scanty. Daily as well as annual range of temperature is high.
In the Himalayas where the southern slopes are protected from cold, northerly winds accessible to the south-west monsoons, there is heavy rainfall on the slopes which are at a height of 1,069-2,286 m above sea level.

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