World Climate Classification Zones
A climate classification groups the world’s climates into zones according to measurable temperature, precipitation and seasonality, and the most widely used system is the Köppen-Geiger classification, which has five main groups: A (tropical), B (dry), C (temperate), D (continental) and E (polar). In brief: the groups are defined mainly by temperature, except for B, which is defined by dryness. A has a coldest month of 18 °C or above, E has a warmest month below 10 °C, C has a coldest month between about 0 or −3 °C and 18 °C, D has a coldest month below that and a warmest month above 10 °C, and B has precipitation below a threshold that depends on temperature.
Classifying climates makes it possible to compare places, to map the zones and to link them to vegetation and land use. This guide explains the Köppen-Geiger system and its subtypes, how to classify a station from monthly data, other systems, compares the groups in a table, works through classification examples, outlines the history and corrects common mistakes.
What are the five main climate groups?
- A: Tropical. All months have a mean temperature of 18 °C or more. Rainfall is heavy for much of the year (rainforest) or has a pronounced dry season (monsoon and savanna).
- B: Dry. Evaporation exceeds precipitation. Deserts (W for the German Wüste) are the driest, and semi-arid steppes (S) are slightly wetter. A third letter, h (hot) or k (cold), gives the temperature.
- C: Temperate (mild). The coldest month is above the threshold of −3 °C (or 0 °C in some versions) but below 18 °C, and at least one month is above 10 °C. Winters are mild, and summers range from warm to hot.
- D: Continental (cold). The coldest month is below the C threshold and the warmest month is above 10 °C. They occur in the interior of large continents in the Northern Hemisphere, with large seasonal ranges.
- E: Polar. The warmest month is below 10 °C. Tundra (ET) has a warmest month between 0 and 10 °C, and ice cap (EF) stays below 0 °C all year.
How are the groups divided?
Further letters describe the rainfall pattern and the temperature of summer. The second letter shows precipitation: f (fully humid, no dry season), m (monsoon), s (dry summer), w (dry winter), and the third letter shows temperature: a (hot summer, warmest month above 22 °C), b (warm summer, with at least four months above 10 °C), c (cool summer, one to three months above 10 °C) and d (very cold winter below −38 °C). Some familiar types are:
- Af: tropical rainforest, such as the Amazon basin, the Congo basin and Indonesia.
- Aw: tropical savanna, with a dry winter, such as East Africa and parts of Brazil.
- BWh: hot desert, such as the Sahara. BSk: cold semi-arid steppe, such as the Great Plains.
- Csa/Csb: Mediterranean, with dry summers, such as southern Europe and California.
- Cfb: oceanic, mild all year with rain in all seasons, as in Western Europe.
- Dfb/Dfc: humid continental and subarctic, as in Central Europe and the boreal forests of Canada and Siberia.
- ET: tundra. EF: ice cap, such as Antarctica and central Greenland.
How do you classify a place?
Collect the mean monthly temperatures and the monthly rainfall for a station, and follow these steps in order.
- If the warmest month is below 10 °C, the climate is E.
- Check dryness. Find the annual mean temperature (MAT) in °C and the annual precipitation (MAP) in mm. Calculate a threshold: if at least 70% of the rain falls in the winter half-year, Pth = 2 × MAT; if at least 70% falls in the summer half-year, Pth = 2 × MAT + 28; otherwise Pth = 2 × MAT + 14. If MAP is less than 10 × Pth, the climate is B, and it is a desert (BW) if MAP is less than 5 × Pth, otherwise a steppe (BS).
- If the coldest month is 18 °C or more, it is A.
- If the coldest month is above the threshold (−3 °C or 0 °C), it is C, and otherwise D.
- Add the second and third letters for the rainfall pattern and the summer temperature.
What other systems exist?
Glenn Trewartha modified the Köppen system in the 1960s, narrowing the definition of tropical and dry climates. The Thornthwaite system (1948) is based on the balance of precipitation and potential evapotranspiration. Climate can also be classified by air masses (Bergeron), by vegetation (biomes) or by the growing season. The Köppen-Geiger system remains the most popular because it uses simple, easily available data. Updated world maps of it are produced from recent data sets, for example by Peel and colleagues in 2007 and Beck and colleagues in 2018, and they show that climate zones are shifting as the world warms.
The main groups compared
| Group | Name | Key temperature rule | Typical vegetation | Example |
|---|---|---|---|---|
| A | Tropical | Coldest month 18 °C or more | Rainforest, savanna | Manaus, Singapore |
| B | Dry | Low rainfall relative to temperature | Desert, steppe | Cairo, Kazakh steppe |
| C | Temperate | Coldest month above −3 °C and below 18 °C | Deciduous and Mediterranean | London, Rome, Sydney |
| D | Continental | Coldest month below −3 °C, warmest above 10 °C | Boreal forest, grassland | Moscow, Winnipeg |
| E | Polar | Warmest month below 10 °C | Tundra, ice | Barrow (Alaska), Antarctica |
Worked example: classifying stations
The data are hypothetical but follow the rules above.
- Station 1: the coldest month is 25 °C, and the driest month has 120 mm of rain. The temperature rule gives A. A driest month with 60 mm or more means that there is no dry season, so the type is Af (tropical rainforest).
- Station 2: the warmest month is 6 °C and the coldest −22 °C. Since the warmest month is below 10 °C, this is E, and as it is above 0 °C, it is ET (tundra).
- Station 3: MAT = 20 °C, MAP = 400 mm, evenly spread through the year. Pth = 2 × 20 + 14 = 54. Then 10 × 54 = 540 mm, and since 400 is below 540, it is a dry climate. Also 5 × 54 = 270 mm and 400 is above 270, so it is a steppe: BS (BSh if the annual mean is 18 °C or more, which applies here).
- Station 4: the coldest month is 8 °C, the warmest month is 25 °C, the driest summer month has 8 mm and the wettest winter month has 90 mm. It is not A (coldest below 18 °C), not B (assuming enough rain), and the coldest month is above −3 °C, so it is C. A dry summer (s) and a warmest month above 22 °C (a) give Csa (Mediterranean).
- Station 5: the coldest month is −18 °C, and the warmest month is 16 °C, with four months above 10 °C and rain all year. It is D, and with no dry season (f) and a warm summer (b), the type is Dfb.
How did climate classification develop?
Ancient Greek writers divided the world into torrid, temperate and frigid zones by latitude. Wladimir Köppen, a Russian-born German climatologist and botanist, published the first version of his climate classification in 1884, based on the boundaries of vegetation types, and refined it in 1900, 1918 and 1936, with the help of Rudolf Geiger, who later revised it. Alexander von Humboldt and others had earlier linked climate and vegetation. The Köppen-Geiger system became a standard reference in schools and research. Today, researchers use satellite and weather station data to update the maps, and they find that many regions have shifted to warmer or drier types over the last decades.
Which mistakes are common?
Mistake 1: Using latitude alone to name a climate
Altitude, distance from the sea, ocean currents and wind patterns also decide the climate.
Mistake 2: Forgetting that B is defined by dryness and not by temperature
A place may be cold or hot and still be a B climate if its rainfall is low relative to evaporation.
Mistake 3: Treating borders as sharp lines
Climate zones grade into each other, and the boundaries are set by thresholds in the system.
Mistake 4: Assuming that the map is fixed
Climate zones shift over time. With the observed warming, many boundaries have moved poleward and to higher altitudes.