G.T. Trewartha (1954) has modified Kopp classification system and has put more emphases the genetic characteristics of climates. His also temperature and precipitation as the basis classification. His scheme, applied to India, country into four major climatic regions divided seven climatic types.
1. Tropical Rainy Climate (Am)-it is chi tried by average annual temperature of 27°C annual rainfall exceeding 250 cm. This climatic prevails over Western Ghats, Tripura and south Assam.
2. Tropical Savannah Climate (Aw)-in climatic type the average annual temperature is and the annual rainfall is 100 cm. It has marke season. It occupies major parts of the Penins India.
3. Tropical Steppe Climate (BS)-here average annual temperature is more than 27°C but the amount of annual rainfall is less than 100 cm. It comprises the rain shadow areas of the Western Ghats occupying central Maharashtra, Karnataka, interior Tamil Nadu and western Andhra Pradesh.
4. Sub-Tropical Steppe Climate (Bsh)-this is a semi-arid region covering parts of Gujarat, eastern and central Rajasthan and southern Haryana. Here the average annual temperature is more than 27°C but the amount of annual rainfall lies between 50 and 100 cm.
5. Tropical Arid Climate (Bwh)-it occupies western Rajasthan and Kachchh region of Gujarat. During summer season the temperature is as high as 48°C while in winter it drops to 12°C showing high seasonal and diurnal range of temperature. The rainfall is scanty (less than 12.5 cm per annum) and highly unreliable. Vegetation is in the form of thorny bushes.
6. Humid Sub-Tropical Climate (Caw)-this resembles to the Cwg climate type by Koppen. It occupies the northern Great Plains from Punjab to Assam. Here average temperature of the winter season is less than 18°C but reaches 46°C to 48°C during summer months. The average annual rainfall is about 62.5 cm but it increases to over 250 cm in the east.
7. Mountain Climate (H)-this region includes the entire Himalayan belt from Kashmir to Arunachal Pradesh. Here average temperature of June lies between 15°C and 17°C but during winter season it falls below 8°C. The rainfall decreases from east to west and in areas of high altitude it is in the form of snow fall. Western parts also enjoy rainfall during winter season by temperate cyclones.