In 1900, the Russian-German climatologist Vladimir Koppen presented the scientific community with a system for classifying the world's climates. Today, it is called the Koppen Climate Classification System. It divides the Earth's surface into climatic regions that generally coincide with world patterns of vegetation and soils. The system has five major climate types. These are based on averages of annual rainfall and temperatures. The annual averages are combined with the monthly rain and temperature statistics. The Koppen System gives each zone a letter name. A is for Moist Tropical Climates, where the temperature is warm all year long, but usually within a narrow range. In addition, there dry seasons followed by wet seasons, which are often the result of monsoon winds.
Zone B is for Dry Climates, which have little rain and a wide daily temperature range, hot in the day and cold at night as radiant heat is returned to outer space. This zone has two subgroups: the semi-arid or steppe regions (S) and arid or desert (W) areas. The C zone is the Humid Middle Latitude Climate, where the land and water differences are the determining factors. These are zones that have warm dry summers and wet, cool winters. D zones have Continental Climates. These climates are in the interior of large landmasses such as central Asia or central North America. The total precipitation can range from low to above moderate. The seasonal temperatures range widely. Zone E climates are the Cold Climates. These are the regions of permanent ice and tundra. Summer temperatures are above freezing, but not enough to melt most of the accumulated ice and snow, or the permafrost.
The Koppen Climate Classification System divides the major five zones into sub-zones. These are assigned a lowercase letter to distinguish specific seasonal characteristics of temperature and precipitation. A lowercase "f" designates zones that are moist year-round. In these zones there is no dry season, with precipitation usually every week or so. The lowercase "f" is usually assigned to zone A, C, and D climates. Lowercase "m" is used to designate rainforest climates. This sub-zone has a short dry season that is monsoon in character, but the rain is enough to create a forest that feeds on a nearly constant rainfall. The lower case "m" sub-zone is assigned to A zone climates. The lowercase "s" stands for the places that have dry season in the summer. This letter applies to summer in both the Northern and Southern Hemispheres. In contrast, lower case "w" is used for localities that have a dry season in the winter. The letter is applied to winter in both the Northern and Southern Hemispheres.
The Koppen Climate Classification System has been refined to account for subtler variations in climates. A third letter is applied to denote these sub-zones. The lowercase letter "a" is used to indicate hot summers where the summertime temperatures are above 72 degrees F (22 degrees C) in the warmest month. Zones C and D are climates where these conditions prevail. The lowercase letter "b" is used to indicate areas where there are warm summers with the warmest month below 72 degrees F (22 degrees C). Again, these conditions are found in Zone C and D climates. Lowercase "c" is used to indicate areas with cool, short summers. In these areas, the summertime lasts less than four months. The temperatures reach over 50 degrees F (10 degrees C). Zone C and D climates have areas with these conditions. Areas with a "d" designation have very cold winters, with the coldest month having temperatures that reach below minus 36 degrees F (minus 38 degrees C). Areas with these conditions are found in the D climate only.
An "h" designation means the area is dry-hot with an average temperature that reaches to above 64 degrees F (18 degrees C). These conditions are found in B climates only. Areas with a lowercase "k" designation have dry-cold climates. These are areas with annual weather conditions where the average temperature does not get above 64 degrees F (18 degrees C). These conditions are found in B climates only.
The climate zones can also be described as Low-Latitude, Tropical Rainforests, Tropical Savanna, Middle-Latitude, Marine West Coast, Humid Continental, Humid Subtropical, Mediterranean, Continental Steppe, High-Latitude, Sub-arctic, Tundra, Polar Ice, Dry Climate, Desert and Highland Climates. All of these zones are related to their location relative to the poles, the temperate zones, the tropics and the equator, in combination with factors of altitude, proximity to the sea, and wind directions. In each one, plants and animals have adapted to the environmental conditions of that zone. The environmental conditions are products of latitude, temperatures, precipitation, elevation, sun exposure, humidity, and the direction of the winds that traverse the region.
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