Koppen Climatic Regions of India: Types, Letters and Areas

Wladimir Koppen was a German climatologist and botanist who published his scheme of world climates in 1918 and revised it several times afterwards. His is an empirical classification, which means it works from figures that are actually measured, the monthly mean temperature and the monthly rainfall, rather than from the causes of climate. Koppen began from the observation that natural vegetation is the best single expression of the climate of a place, so his boundaries follow the limits of vegetation belts. For Indian geography papers the chapter is small and highly scoring: learn the letters, then learn which part of India carries which code.

How the letter code is built

A Koppen code has a capital letter for the major group and one or two small letters that describe the season of rain and the character of temperature. The five major groups are A for tropical, B for dry, C for warm temperate, D for cold snow forest and E for cold polar climates. Four of these are decided by temperature alone; only B, the dry group, is decided by the relation between rainfall and evaporation.

The eight climatic regions of India

Applied to India the scheme yields eight types. They run from the wet tropical codes of the coasts, through the dry codes of the north-west, to the cold codes of the mountains.

Reading the map region by region

The Malabar coast south of Goa is given Amw because it is hot throughout the year and receives very heavy rain from the south-west monsoon, leaving only a short dry spell. The Coromandel coast is given As, the only place in India with a dry summer code, because its main rain comes not in June to September but from the retreating monsoon and the north-east monsoon between October and December. The bulk of the Deccan plateau is Aw, the savannah type, with a long dry season and moderate summer rain. Moving north-west, rainfall falls away: the steppe code BShw covers north-western Gujarat and parts of western Rajasthan and Punjab, and in the extreme west of Rajasthan, in the Thar, the full desert code BWhw appears. The Ganga plain is Cwg; here the small letter g marks what Koppen called the Gangetic type of temperature, in which the hottest month comes before the solstice and the onset of the rains rather than after it. In the eastern Himalaya, Arunachal Pradesh is the only part of India with the Dfc code, a cold and humid winter with a summer of less than four months above 10 degrees Celsius. Above the tree line in the western and central Himalaya the warmest month stays below 10 degrees Celsius, which gives the E or polar type with its tundra and ice-cap variants.

Other schemes you should be able to name

Koppen is not the only classification in the syllabus. C. W. Thornthwaite built a rational classification on the water balance, using precipitation effectiveness and thermal efficiency instead of vegetation. Glenn Trewartha produced a simplified revision of Koppen. Stamp and Kendrew divided India into regions on the basis of the January isotherm of 18 degrees Celsius and the annual rainfall. The India Meteorological Department uses its own working divisions for forecasting. Questions usually ask only which scheme is empirical, which is genetic and which is rational: Koppen is empirical, Thornthwaite is rational, and schemes built on air masses and pressure belts are genetic.