Unit 4: The Atmosphere and the Oceans Chapter 14: Climate     Climate The most commonly used system to classify climates was developed in 1900 by Wladimir Koeppen, a Russian-born scientist who spent much of his life studying climatology. The climate map in your textbook is a modified version of Koeppen's system. The original system used both uppercase and lowercase letters to distinguish among different types of climate. Main Climate Types After years of study and revision, Koeppen came up with five main climate types based on three factors: precipitation, temperature, and vegetation. Each of the main categories is designated by an uppercase letter. The main categories include: A. Tropical forest B. Dry C. Warm temperate rainy D. Cold forest E. Polar In tropical forest climates (A), average monthly temperatures are above 18°C. In dry climates (B), rates of evaporation exceed those of precipitation. Thus, there is always a moisture deficit in these areas. The average temperature of the coldest month in warm temperate rainy climates (C) is below 18°C, but above 0°C. In cold forest climates (D), the average temperature of the coldest month is below 0°C and the average temperature of the warmest month is above 10°C. In polar climates (E), the average temperature of the warmest month is below 10°C. Note that four of the major groups are classified according to temperature, while the fifth group-dry climates-is classified according to precipitation. This is because dry climates vary greatly in temperature; the unifying factor that binds them together is the amount of precipitation that they receive. Subdivisions Koeppen furthered subdivided the five main climate types into smaller groups, as shown in Table 1. The second letter in each category refers to the amount of precipitation received by an area. The third letter refers to its temperature. Thus, a climate that is classified as Dfc is a cold forest climate (D) that is moist year round (f) with short cool summers (c). Table 1 also includes a sixth main category, highland climates (H). These climates are found at high elevations and are similar to polar climates. As you study this classification system, keep in mind that one climate zone does not abruptly change into another. Rather, the transitions between zones are gradual and sometimes overlap. Table 1 Koeppen Classification System Climate Description Af Tropical rain forest; hot year round; rainy year round Am Tropical monsoon; hot year round; seasonally wet Aw Tropical savanna; hot year round; seasonally dry BSh Tropical steppe; semiarid; hot year round BSk Midlatitude steppe; semiarid; cool or cold BWh Tropical desert; arid; hot year round BWk Midlatitude desert; arid; cool or cold Cfa Humid subtropical; moist year round; long, hot summer Cfb Marine; moist year round; warm summer Cfc Marine; moist year round; short, cool summer Csa Continental Mediterranean; dry summer; hot summer Csb Coastal Mediterranean; dry summer; short, warm summer Cwa Subtropical monsoon; dry winter; hot summer Cwb Tropical continental; dry winter; short, warm summer Dfa Humid continental; moist year round; long, hot summer Dfb Humid continental; moist year round; short, warm summer Dfc Subarctic; moist year round; short, cool summer Dfd Subarctic; moist year round; short summer Dwa Humid continental; dry winter; long, hot summer Dwb Humid continental; dry winter; warm summer Dwc Subarctic; dry winter; short, cool summer Dwd Subarctic; extremely cold, dry winter; short, cool summer ET Tundra; extremely short summer EF Year-round ice cover H Highland Classifying Koeppen's System Scientists use different methods to develop classification systems. Most climate systems use either a genetic method or an empirical method. A genetic method classifies climates according to the factors that cause climates to differ, such as latitude. An empirical method classifies climates according to the observed characteristics of the climates, such as vegetation. Koeppen's system actually uses both methods. It is a genetic-empirical classification scheme. This is partly why it has remained such a useful tool for studying climates. LINK-UP: Find more information on classifying climates. Activity Develop a classification system that, like Koeppen's climate system, uses uppercase and lowercase letters to designate main categories and subcategories. Describe your classification system in your science journal. What did you classify? What criteria did you use?