From AMS Glossary
A climatic classification scheme developed by Wladimir Köppen (1846– 1940), a German climatologist.
This scheme is based upon annual and monthly means of temperature and precipitation and also takes into account the vegetation limits. It is a tool for presenting the world pattern of climate and for identifying important deviations from this pattern.
Köppen, W. P., and R. Geiger 1930–1939. Handbuch der Klimatologie. Berlin: Gebruder Borntraeger, 6 vols.