Brief Guide to Koeppen Climate Classification System

Class A: Tropical

Temperature of the coldest month: > 18°C. This the climate where the most water- and heat-demanding crops (e.g. for instance oilpalm and rubber) are grown. The climate is also ideal for yams, cassava, maize, rice, bananas and sugarcane. Sub-classes are:

Af - No dry season, at least 60 mm of rainfall in the driest month
Am - Monsoon type. Short dry season but sufficient moisture to keep ground wet throughout the year.
Aw - Distinct dry season. One month with precipitation < 60 mm.
i - Isothermal subtype. Annual range of temperature < 5°C

Class B: Dry

Arid regions where annual evaporation exceeds annual precipitation. Even the wettest variants of this climate are characterized by a marked dry season. The climate is, therefore, mostly unsuitable for the crops that require year-round moisture. The main crops are usually millet, sorghum and groundnuts. Sunshine is usually high, which leads to high productivity where a sufficiently long rainy season or irrigation ensure a sufficient water supply: rice, sugarcane and maize are also common crops under this climate.

The two main subclasses refer to the dominant vegetation types: BS (steppe climate) and BW (desert). They are further subdivided as h subtype (subtropical desert with average temperature > 18°C), k subtype (cool dry climate of the middle latitude deserts), and k' (temperature of the warmest month < 18 °C).

Class C: Temperate

Average temperature of the coldest month < 18°C and > -3°C , and average temperature of warmest month >10°C. The main crops are the temperate cereals such as wheat, barley and Irish (white) potatoes. An important variant of this climate is the Mediterranean climate, characterized by the olive tree, and also very suitable for grapes. The main subdivisions include:

Cw - Winter dry season. At least 10 times as much precipitation in wettest month of summer as in driest month of winter
Cs - Summer dry season. At least three times as much rain in wettest month of winter as in driest month of summer, the latter having less than 30mm precipitation.
Cf - At least 30 mm precipitation in the driest month, difference between wettest month and driest month less than for Cw and Cs

Additional qualifiers are a (hot summer, average temperature of warmest month > 22°C), b (cool summer, average temperature of warmest month < 22°C) and c (cool - short summer less than four months >10°C). Note that the "raw" temperate climate extends into what is actually BS and BW, as the "Dry" B type is superposed on the other types where only temperature is used to define the climate.

Class D: Cold

Average temperature of the warmest month > 10°C and that of coldest month < -3°C. This climate grows essentially the same crops as the temperate climate, but seasons tend to be shorter and limited at the beginning and end by frost.

This climate type comprises mainly the Df subtype (at least 30 mm of rain in the driest month, difference between wettest month and driest month less than for Cw and Cs) and Dw (winter dry season - at least 10 times as much precipitation in wettest month of summer as in driest month of winter). Other codes used are: a (hot summer, average temperature of warmest month > 22°C), b (cool summer, average temperature of warmest month < 22°C), c (cool, short summer less than four months > 10°C) and d (average temperature of coldest month < -38°C).

Class E: Polar

Average temperature of the warmest month < 10°C. No crops are grown under this climate. The two main subdivisions - ET (tundra, average temperature of warmest month > 0°C), and EF (no month with temperature > 10°C) - are sometimes qualified by d if the average temperature of coldest month < -38°C.