Class A: Tropical
Temperature of the coldest month: > 18°C. This the
climate where the most water- and heat-demanding crops (for
instance oil palm and rubber) are grown. The climate is also
ideal for yams, cassava, maize, rice, bananas and sugarcane.
Af - No dry season, at least 60 mm of rainfall in the driest
Am - Monsoon type. Short dry season but sufficient moisture
to keep ground wet throughout the year.
Aw - Distinct dry season. One month with precipitation <
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
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