The classification of climate zones is based on a model created by W. Lauer and P. Frankenberg in 1985. The criteria for classification refer to the natural vegetation. The basic principle for the definition of climate zones is the inclusion of solar-climatical conditions of irradiation and illumination. The borderline of the tropics is defined by the fluctuation of temperature: the border is located where the temperature variation between summer and winter (annual amplitude) is larger than the variation between day and night (diurnal amplitude). Tropical climates are consequently diurnal climates, whereas ectropical climates are annual climates.
According to that climatic classification, the earth can be divided roughly into four climatic zones, defined by the sun irradiation. These zones are subclassified into climatic regions based on their thermal properties. The classification of aridity and humidity derives from the number of humid months. A month is defined as humid when the average amount of precipitation is higher than the evaporation.
A - tropical
B - subtropical
C - temperate (moderately warm = I and cold = II)
D - polar regions
SUBCLASSIFICATION OF THE TROPICS:
1 - cold tropical
2 - warm tropical
SUBCLASSIFICATION OF OTHER CLASSES
1 - high-continental
2 - continental
3 - maritime
a - arid (0-2 rainy months)
sa - semi-arid (3-5 rainy months)
sh - semi-humid (6-9 rainy months)
h - humid (10-12 rainy months).