CDS (II) 2020 General Knowledge · Question 10 of 120

Correct — A, Aw. In Köppen's scheme the first letter gives the broad group and the second the precipitation pattern. A is the tropical group, where every month averages above 18 degrees Celsius, and w means a dry winter. Aw is therefore the tropical wet and dry climate, the savanna type: a rainy high-sun season followed by a pronounced dry season in which the driest month gets less than 60 mm. That alternation is what produces tall coarse grassland with scattered fire-resistant trees such as acacia and baobab, and it is why the same climate carries the llanos of the Orinoco, the campos of Brazil and the savannas of northern Australia as well as the African belt the name comes from.

• (b)Dfc — A subarctic climate — D for continental with the coldest month below zero, f for no dry season, c for only one to three months above 10 degrees. This is the taiga, about as far from savanna as the scheme goes.
• (c)Cwg — A warm temperate climate with a dry winter — the notation Indian textbooks use for the monsoon type of the Ganga plain, where the hottest month comes before the rains. Warm temperate, not tropical.
• (d)Am — The tropical monsoon climate. It shares the A group with savanna but has a short dry season and a very heavy wet one, so the total is high enough to carry forest rather than grassland.

Köppen classified climates by the temperature and rainfall thresholds at which natural vegetation changes, which is why his letters map so neatly onto biomes. Five main groups are used: A tropical, B arid, C warm temperate, D continental and E polar. A second letter describes the seasonal rainfall — f for no dry season, m for monsoon, w for a dry winter, s for a dry summer — and a third letter, where used, describes temperature detail. The Indian codes that follow this pattern include Amw for the monsoon type with a short dry season, As for the monsoon with dry summers on the Coromandel coast, Aw for the savanna type over much of the southern peninsula, BWhw for the hot desert of western Rajasthan, BShw for the semi-arid steppe around it, Cwg for the monsoon type with dry winters over the Ganga plain, Dfc for the cold humid winter type of the north-east and E for the polar type of the high Himalaya.

The letters are the whole battle. Start with the first: savanna is hot all year, so the code has to begin with A, which immediately removes Dfc and Cwg. Between the two survivors, Am and Aw, the distinction is how severe the dry season is — m for a short one with a very wet remainder, w for a long, clearly marked dry winter. Grassland with scattered trees needs the long dry season, because a season dry enough and long enough to burn is exactly what keeps a closed forest from establishing. That is also why the savanna is a fire-maintained landscape rather than simply a dry one.

• In Köppen's scheme A denotes a tropical climate where the coolest month still averages above 18 degrees Celsius.
• The second letter w means a dry winter, so Aw is the tropical wet and dry or savanna climate; its driest month receives less than 60 mm.
• Am is the tropical monsoon climate — a brief dry season carried by a very heavy wet one.
• Dfc is a subarctic climate with only one to three months averaging above 10 degrees Celsius.
• Savanna grassland is maintained by the dry season and by fire; without them, closed woodland would take over much of the same area.

• Reading the second letter before the first. The group letter settles half the question on its own.
• Treating Am and Aw as interchangeable because both are tropical and both have a dry season.
• Assuming Cwg must be tropical because it describes the monsoon. The C group is warm temperate.

As a code-to-climate item in either direction, or as a which-code-fits-this-Indian-region item such as western Rajasthan or the Ganga plain.

• practice — not a real PYQ

  In Köppen's classification, the first letter of the code for a savanna climate is A because of which one of the following?

  • (a)The annual rainfall exceeds 200 cm
  • (b)Every month averages above 18 degrees Celsius
  • (c)There is no dry season
  • (d)It lies exactly on the Equator

  Answer(b) Every month averages above 18 degrees Celsius — that temperature threshold is what defines Köppen's A or tropical group, whatever the rainfall pattern.

• practice — not a real PYQ

  Which one of the following Köppen codes best describes the climate of the western fringe of Rajasthan?

  • (a)Aw
  • (b)Am
  • (c)BWhw
  • (d)Cwg

  Answer(c) BWhw — B for arid, W for desert rather than steppe, h for hot and w for a dry winter, which is the hot desert of the western Thar.