Geography Quiz: Köppen's Climatic Regions of India

Koppen, who was a botanist as well as a climatologist, held that natural vegetation is the best single index of climate, and he fixed his boundaries using the monthly values of temperature and rainfall that vegetation belts seem to follow.

The code stands for a monsoon climate with a short dry season: the Malabar coast is hot in every month, so the capital A applies, and it receives extremely heavy rain from the south-west monsoon, leaving only a brief dry spell.

This coast lies in the rain shadow of the Western Ghats while the south-west monsoon blows, so its summer is comparatively dry, and it gets most of its rain between October and December from the retreating monsoon and the north-east monsoon, which is exactly what the small letter s records.

The capital B marks a dry climate, the capital W marks the arid or desert subdivision, h marks a hot climate and the last w marks a dry winter, so the whole code describes the heart of the Thar, the driest part of the country.

The capital D marks a cold snow forest climate in which the coldest month falls below minus three degrees Celsius, f marks the absence of a dry season and c marks a short summer with fewer than four months above ten degrees Celsius, and in the standard table for India…

Over most of the Ganga plain the temperature rises steadily through the spring and peaks in May, before the rains break, after which cloud and moisture bring the readings down, and Koppen gave this particular annual march of temperature its own letter.

The interior of the Deccan is hot in every month, which gives it the capital A, and it has a long dry season with moderate rain in summer, which gives it the small letter w, the classic savannah combination.

Within the dry B group Koppen used two capital letters for the degree of dryness, S for the steppe, which is semi-arid, and W for the desert, which is fully arid, so BShw describes a hot semi-arid climate with a dry winter.

Koppen set the boundary of the tropical group at a mean temperature of 18 degrees Celsius in the coldest month, the value below which many tropical plants cannot thrive, and the whole of peninsular India as well as both coasts clears it.

Koppen was born in Russia and worked in Germany, and his training in plant science is the reason his classification uses natural vegetation as the index of climate and sets its boundaries where vegetation belts change.

C. W. Thornthwaite measured precipitation effectiveness and thermal efficiency, that is, the balance between the water a place receives and the water it loses to evaporation and transpiration, and because these are derived quantities rather than raw readings his scheme is called rational.

Above the tree line in the western and central Himalaya the mean temperature of even the warmest month stays below ten degrees Celsius, which is the defining condition of the E group, and the tundra and ice-cap variants of that group occupy the high valleys and the snowfields.