• Climatic regions have homogeneous climatic conditions resulting from a combination of factors.
• Temperature and rainfall are key elements considered in climatic classification schemes.
• India as a whole has a monsoon type of climate, but there are regional variations due to different combinations of weather elements.

• India can be divided into different climatic regions based on variations in climate distribution
• The Trewartha scheme is suitable for India and corresponds closely to soil, vegetation, and agricultural regions
• Trewartha modified Koppen’s classification of climate in 1954
• Trewartha’s classification is empirical and based on temperature and precipitation data
• English alphabets are used as symbols to show the different types of climate
• India is divided into four major climatic regions and seven meso-climatic divisions according to Trewartha’s scheme

Trewartha’s Classification of Climate

According to Trewartha’s scheme, the main climatic regions of India include:

• Tropical Rainforest Climate (Am)
  • High temperatures and heavy precipitation
  • Temperatures above 18.2°C, rainfall above 200cm
  • Includes western coastal plain, Sahyadris, Assam, and Meghalaya
  • Dense evergreen forests
• Tropical Savannah Climate (Aw)
  • Mean annual temperature around 27°C
  • Mean annual rainfall less than 100 cm
  • Marked dry season
  • Covers most of Peninsular India, excluding coastal plains and western slopes of Western Ghats
• Tropical Steppe Climate (BS)
  • Mean annual temperature around 27°C
  • Rain-shadow area of Western Ghats
  • Covers peninsular India east of Western Ghats
• Sub-tropical Steppe Climate (BSh)
  • Semi-arid climate in parts of Gujarat, eastern Rajasthan, Mahanadi, Andhra Pradesh, and southern Haryana
  • Mean annual temperature over 27°C, mean monthly January temperature around 15°C
  • Mean annual rainfall varies between 60-75 cm
• Tropical Arid Climate (BWh)
  • Found to the west of the Aravallis, stretching over the Thar Desert
  • Mean maximum temperature during May and June occasionally crosses 48°C
  • Mean annual rainfall less than 25 cm, lowest rainfall in Ganganagar district
  • Natural vegetation in the form of thorny bushes
• Humid Subtropical Climate (Caw)
  • Occupies most of the Great Plains of India, from Punjab to Assam
  • Mean January temperature less than 18°C, mean maximum in summer may cross 45°C
  • Average annual rainfall varies from 250 cm in east to about 65 cm in west
• Mountain Climate (H)
  • Found in hilly parts of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Arunachal Pradesh, and other hilly parts of northeast India
  • Average temperature for summer season around 17°C, average January temperature around 8°C
  • Rainfall decreases from east to west, Western Himalayas record some rainfall from western disturbances during winter season.