Gloria Glover The Köppen classification sorts climates by long-term averages of air temperature and precipitation. The Köppen climate classification system uses monthly thresholds, rainfall timing, and dry-climate formulas to connect recurring weather patterns with the vegetation they can support. Its full codes have two or three letters, so the first letter is only the broadest level.
Reading a code shows whether a place is humid, seasonally dry, temperate, continental, or polar, then adds detail about rainfall and summer or winter temperatures.
What the Köppen classification measures
Climatologists calculate long-term monthly mean temperatures and precipitation totals rather than relying on one season or unusual year. Temperature thresholds separate tropical, temperate, continental, and polar conditions; precipitation rules identify moist climates and the timing of dry seasons.
For dry climates, the system compares annual precipitation with a threshold based on mean temperature and the share of rainfall arriving in summer or winter. This prevents a hot desert and a cold steppe from being grouped merely because both are dry. The method reflects broad vegetation patterns, not every local microclimate.
How the Köppen climate classification system organizes climates
The first character identifies one of five major groups. It narrows the climate family, but it is not a complete Köppen climate code.
Groups A and B: tropical and dry climates
- A: Tropical. Every month averages at least 18°C. Later letters show whether rainfall is year-round, monsoonal, or seasonally dry.
- B: Dry. Precipitation falls below the system’s temperature-adjusted threshold. S means steppe and W means desert; a final h or k indicates hot or cold conditions.
Groups C, D, and E: temperate, continental, and polar climates
- C: Temperate. Winters are mild and the warmest month exceeds 10°C. The coldest-month boundary is commonly 0°C or -3°C, depending on the version used.
- D: Continental. Winters are more severe than in C, while at least one month exceeds 10°C, creating strong seasonal contrast.
- E: Polar. The warmest month stays below 10°C. T means tundra; F means ice cap.
How secondary and tertiary letters shape Köppen climate zones
After the first letter, the additional characters describe moisture seasonality and thermal intensity. Their meanings depend on the major group.
Reading the second letter: rainfall seasonality or dryness
In A climates, the second letter is f for no dry season, m for monsoon, or w for dry winter. In C and D climates, it is f for no dry season, s for dry summer, or w for dry winter. B climates instead use S and W for steppe and desert. These letters describe moisture distribution, not simply annual rainfall.
Reading the third letter: heat and cold details
A third letter mainly refines heat in C and D climates: a means hot summer, b warm summer, c a cool, short summer, and d an exceptionally cold winter. In B climates, h means hot and k cold. E climates stop at two letters because T or F already supplies the key thermal detail.
Complete Köppen climate codes in real regions
We can decode each full code from left to right:
Five full codes: Af, BWh, Csa, Dfc, and ET
- Af — Singapore: A is tropical, and f indicates rainfall in every month.
- BWh — the Sahara: B is dry, W specifies desert, and h marks a hot climate.
- Csa — Athens: C is temperate, s means dry summer, and a indicates a hot summer.
- Dfc — Anchorage: D is continental, f means no dry season, and c indicates a cool, short summer.
- ET — Utqiagvik, Alaska: E is polar and T means tundra; no third letter is used.
