Koeppen's classification of world climates

In Köppen’s dry group, BW denotes desert and BS denotes steppe. Desert climate has a greater moisture deficit: precipitation is lower relative to the water demand created by evaporation. Steppe climate is semi-arid and receives more effective moisture than desert climate. Temperature alone does not decide the comparison, because the classification considers both precipitation and evaporative demand.

In dry-climate codes, the lowercase h indicates a hot thermal condition, commonly defined by a mean annual temperature of 18°C or more. Thus BWh means hot desert and BSh means hot steppe. The letter k is used for the colder dry subtype, while h does not mean humid; moisture conditions are represented by the main dry-group code and related criteria.

The lowercase k is used in dry-climate codes for the colder subtype, generally where the mean annual temperature is below 18°C. Therefore BWk is a cold desert and BSk is a cold steppe. By contrast, h marks the hot subtype. The symbols for dry summer and rainforest describe precipitation patterns in other parts of the classification, so they are not the meaning of k here.

The first letter C places the climate in the warm-temperate group, while the suffix w indicates a dry winter. Therefore Cw has its main dry season in winter and generally wetter conditions in summer. This differs from Cs, which has a dry summer, and Cf, which has no distinct dry season. The symbol w should be read as winter-dry in this context.

In the C group, the suffix s means a dry summer. Consequently, Cs climates have little summer rainfall and comparatively wetter winters; the Mediterranean climate is the standard example. This is the reverse of Cw, where winter is dry. Cf means that no distinct dry season exists. Thus summer, not winter or spring, is the correct answer.

C identifies the warm-temperate climate group, and f indicates that no distinct dry season occurs. Therefore Cf is a humid temperate climate with precipitation distributed through the year, even if monthly amounts vary. Cs has a dry summer and Cw a dry winter. The polar group is E, so option D does not fit the code.

Group D is the cold or snow-forest, also called continental, climate group in the traditional Köppen scheme. It is marked by a substantial seasonal temperature range, including cold winters, and is common in continental interiors and higher mid-latitudes. Tropical rainforest is Group A, hot desert is Group B, and ice-cap climate is EF in Group E.

Group E represents polar climates, where temperatures remain very low. It includes ET tundra, in which the warmest month is above 0°C but below 10°C, and EF ice-cap climate, in which no month has a mean temperature above 0°C. Thus very cold is the broad defining condition; rainfall alone does not classify this group.

Both Af and Aw begin with A, so both belong to the tropical rainy climate group. Af is tropical rainforest, with no distinct dry season, whereas Aw is tropical savanna, with a dry winter or dry season. Their rainfall distributions differ, but their year-round warmth places them in the same main group. B, C and E represent dry, temperate and polar groups.

BW and BS both begin with B, the main group for dry climates. The second letter distinguishes their degree of aridity: W represents desert and S represents steppe or semi-arid conditions. Thus BW is drier than BS, but both are still part of Group B. C, A and E refer to temperate, tropical and polar groups, respectively.

The first letter gives the broad climate group: A tropical, B dry, C warm temperate, D cold or snow-forest/continental, and E polar. Later letters add information about rainfall seasonality or temperature characteristics. Therefore the first letter is not a numerical rainfall total or a single month’s temperature. It provides the basic framework for interpreting the complete code.

The second letter commonly describes precipitation pattern or the presence and timing of a dry season. For example, f means no distinct dry season, s means dry summer, and w means dry winter in many A, C and D codes. In dry climates, W and S distinguish desert from steppe. Population, minerals and crop prices are not parts of the climate code.

In many three-letter Köppen codes, the third letter adds a temperature detail. In C and D climates, a, b, c and d describe the warmth or length of summer and the severity of winter; in B climates, h and k distinguish hot and cold dry conditions. The exact meaning depends on the group, but it is related to temperature, not language, ocean depth or politics.

In many C and D climate codes, the third letter a indicates a hot summer. The mean temperature of the warmest month is generally at least 22°C, and the climate usually has a sufficiently warm season. Letter b indicates a warm but less hot summer, while c indicates a short and cool summer. Thus (a) does not mean merely warm or the absence of summer.

In many C and D codes, the letter b describes a warm or mild summer that is not as hot as the summer marked a. The warmest month is generally below 22°C, while at least some months are sufficiently warm for a recognizable summer. It is a temperature symbol, not a desert, polar or rainfall-season symbol. Cfb is a familiar example of a climate with b.

Köppen’s classification organizes the world’s climates into recognizable groups using temperature and precipitation patterns, with links to natural vegetation. This makes it easier to compare regions, interpret climate maps and relate climate to ecosystems. It is not a method for dating rivers, counting population or naming soil chemicals. Those subjects require different geographical or scientific classifications.

Köppen recognized that natural vegetation reflects the combined influence of temperature and moisture over time. Therefore vegetation zones helped him identify and describe climate boundaries, while the classification itself uses measurable climatic conditions such as temperature and precipitation. Roads, industrial output and language boundaries are human or cultural features and do not provide the natural basis of Köppen’s climate groups.

Group A is the tropical climate group. Its defining temperature condition is that the mean temperature of every month is generally 18°C or higher, so there is no truly cold season in the ordinary sense. Rainfall patterns then separate Af, Am and Aw. Ice-cap, very cold and cold-desert conditions belong to other groups, especially E or cold forms of B.

In the relevant Köppen codes, f means that no distinct dry season occurs; precipitation or moisture is available throughout the year, although its amount may vary from month to month. Af therefore represents tropical rainforest, and Cf represents humid temperate climate without a marked dry season. Dry summer is s, dry winter is w, and f does not mean snow in every season.

In the Köppen system, the lowercase letters w and s describe the season in which precipitation is least. w means a dry winter, while s means a dry summer. Thus, the first option correctly gives their contrast. The letters do not identify snow, deserts, or tundra by themselves; those conditions are represented through the main group and other code letters.

In the Köppen classification, the capital letter E identifies the polar climate group. ET is the tundra climate: E marks polar conditions and T distinguishes tundra from EF ice-cap climate. Af belongs to the tropical group, Cfa to the temperate group, and BSh to the dry group. Therefore, ET is the only polar code among the choices.

The capital letter B is the Köppen code for dry climates, which include deserts and steppes. BWh is a hot desert code: BW identifies desert conditions and the final h indicates a hot climate. Cfb is temperate marine, Af is tropical rainforest, and EF is polar ice cap. Hence BWh is the only dry-group code listed.

Köppen’s system primarily uses measurable climatic elements, especially temperature and precipitation, to divide the world into major climate groups and subtypes. Temperature thresholds identify broad groups, while the amount and seasonal distribution of rainfall help distinguish their subcategories. Soil, population, language, and culture may be influenced by climate, but they are not the basic criteria of this classification.

The capital letter A represents the tropical climate group in the Köppen system. These climates generally have a mean temperature of at least 18°C in every month, although their rainfall patterns may differ, producing Af, Am, or Aw types. B represents dry climates, C temperate climates, and E polar climates, so A is the correct choice.

B is the capital letter used for the dry climate group in the Köppen classification. This group includes BW desert climates and BS semi-arid or steppe climates; its definition depends on the relationship between precipitation and potential evaporation. A denotes tropical, C temperate, and E polar climates. Therefore, B is the unambiguous answer.