The Terrestrial Climate and its classification
The system of classification of climates normally adopted, based on the differences in temperature and precipitations, is that formulated by the German climatologist Wladimir Köppen at the beginning of the XX century. Its base consists of the observation that the most evident and direct effect of the climate is the type of vegetation associated with it. As a result of this, the Earth is subdivided into five great climatic areas, each corresponding to the area of distribution of a particular category of plants.
These plants are in fact divided into five classes, according to the environmental conditions which they need: the megathermic grow in presence of medium temperatures above 20 °C; the mesothermic are typical of the temperatures between 15 and 20 °C; the microthermic are characteristic of the temperatures between 0 and 15 °C; the echistothermic grow in the presence of very low temperatures, beyond the limit of the arboreal vegetation; finally the xerophytes are the plants which have adapted to arid environments, characterized by long periods of drought.
According to this classification of vegetation five great climatic areas can be distinguished: that of the humid tropical climates, corresponding to the area in which megathermic plants are diffused; that of the arid climates, in which xerophyte plants grow; that of the moderate-warm climates, in which the mesothermic plants are found; that of the northern climates, corresponding to the area in which microthermic plants are distributed, and finally, the polar zone, in which echistothermic plants grow.
Af = tropical climate without arid season
Aw = tropical climate with dry winter
BS = arid climate of the steppe
BW = arid climate of the desert
Cf = warm moderate climate without dry season
Cs = warm moderate climate with dry summer
Cw = warm moderate climate with dry winter
Df = cold moderate climate without dry season
Dw = cold moderate climate with dry winter
ET = cold climate of the tundra
EF = cold climate of perennial ice