The Koppen Climate Classification System is the most widely used system for classifying the world's climates. Its categories are based on the annual and monthly averages of temperature and precipitation. The Koppen system recognizes five major climatic types; each type is designated by a capital letter.
A - Tropical Moist Climates: all months have average temperatures above 18° Celsius.
B - Dry Climates: with deficient precipitation during most of the year.
C - Moist Mid-latitude Climates: with Mild Winters.
D - Moist Mid-Latitude Climates: with Cold Winters.
E - Polar Climates: with extremely cold winters and summers.