Gloria Glover The Köppen climate classification chart turns long-term temperature and precipitation patterns into a short code. We can read each label from left to right: the first letter identifies the broad climate group, while later letters show seasonal rainfall and temperature conditions.
The Köppen climate classification system helps us compare places without treating a whole state as one climate. Readers can compare climate zones in the US, from tropical rainforest to polar tundra, with dry, temperate, and continental types in between.
How the Köppen Climate Classification Chart Is Organized
Temperature and precipitation thresholds
Each code begins with a broad temperature or precipitation regime. In the standard logic, A means every month averages at least 18°C; B means precipitation is low enough to meet a dryness threshold; C has a mild winter; D has a colder winter and a warmest month above 10°C; and E has a warmest month below 10°C. For B climates, the threshold also adjusts for annual temperature and whether rainfall is concentrated in summer or winter.
Reading a code from first letter to final modifier
Start with the first letter, identify the seasonal precipitation pattern with the next letter, and then use the final letter for summer or winter temperature conditions. The letters work as a sequence: Cfa means C, f, and a, not one indivisible category.
The Köppen Climate Classification System: Five Major Groups
- A: Tropical. All months remain warm; rainfall patterns distinguish rainforest, monsoon, and savanna climates.
- B: Dry. Evaporation demand exceeds available precipitation, creating desert or steppe conditions.
- C: Temperate. Winters are mild, while summers range from warm to hot.
- D: Continental. Winters are colder, with substantial seasonal temperature contrast.
- E: Polar. The warmest month stays below 10°C, producing tundra or ice-cap conditions.
How Secondary and Tertiary Letters Work
Seasonal precipitation letters: f, s, w, and m
For C and D climates, f means no dry season, s means a dry summer, and w means a dry winter. In tropical climates, m identifies a monsoon pattern; f, w, and sometimes s describe other rainfall patterns. In B climates, the second letter instead separates W desert from S steppe.
Temperature modifiers: a, b, c, d, h, and k
For C and D climates, a indicates a hot summer, with the hottest month at or above 22°C. b indicates a warm but not hot summer, c a short, cool summer, and d an especially severe winter. For B climates, h means a hot annual average of at least 18°C, while k means a colder annual average.
Complete-code walkthroughs: Cfa, Dfb, and BSk
- Cfa: temperate, no dry season, hot summer. This is the humid subtropical pattern.
- Dfb: continental, no dry season, warm summer. It has four or more months above 10°C but no month reaching the hot-summer threshold.
- BSk: dry, steppe, cold. It describes a cold semi-arid climate rather than a desert.
Köppen Climate Zones in the US: Representative Regional Codes
Humid East and central interior locations: Cfa, Dfa, and Dfb
Atlanta is representative of Cfa, with humid conditions, rainfall in every season, and hot summers. Chicago commonly represents Dfa: a humid continental climate with hot summers and cold winters. Minneapolis and many northern interior locations are often Dfb, with warm rather than hot summers.
Dry Southwest and Pacific coast locations: BWh, BWk, Csa, and Csb
Phoenix is a clear BWh example: hot desert. Cold desert pockets in the Great Basin can be BWk, while nearby semi-arid basins may be BSk. Southern California coast locations commonly show Csa, a dry-summer climate with hot summers. Farther north, parts of the California and Oregon coasts show Csb, with dry summers that are warm rather than hot.
Selected Alaska and Hawaii locations: Dfc, ET, and Af
Fairbanks illustrates Dfc, a subarctic climate with no dry season and a short, cool summer. Utqiagvik is typically ET, or tundra. Hilo, Hawaii, represents Af, tropical rainforest. Local elevation, coastlines, and rainfall shadows can change the code within a region, so no single Köppen label covers an entire U.S. state.
