Trewartha modified Koeppen’s Classification. He divided the country into 4 major and 7 sub-types.
1. A type Climate.
This type of climate has tropical rainfall, high temperature and temperature over 18°C in the coldest month. It has 2 sub-types.
It is characterized by over 27°C mean annual temperature. Annual rainfall is over 250 cm. The areas are Western Coast, S. Assam, West Bengal and Tripura.
It is characterized by 27°C mean annual temperatures. The annual rainfall is 100 cm. It comes in summer. Sawannah type of vegetation grows. It covers a large part of Peninsula.
2. B type Climate.
It is characterized by dry conditions. It has three sub-types. (i) Bsh. It is characterized by 27°C mean annual temperature.
Annual rainfall is 50-100 cm. Grassland vegetation grows. It covers Eastern Rajasthan and Gujarat.
Hot and Semi-desert climate as in Thar Desert of India.
(iii) Bs. Semi-arid tropical Savannah climate with 27°C mean annual temperature. Annual rainfall is 100 cm. Such climate prevails in the rain shadow areas.
3. C Type Climate.
Sub-Tropical Climate. It has one sub-type.
Dry climate and rainfall in winter due to cyclones. Such climate is from Punjab to Assam.
4. H Type Climate.
Mountain type Climate. It is characterized by low temperature and snowfall in winter. It is experienced in the Himalayan Zone.