The Köppen climate classification, explained

What is the Köppen-Geiger climate classification?

The climatologist Wladimir Köppen developed the classification in the late 19th century, and Rudolf Geiger later refined it. It divides land climates into five major classes and 30 sub-classes using thresholds and the seasonality of monthly air temperature and precipitation.

Drawing on his work as a botanist, Köppen designed the classes to line up with the world's major vegetation types, so that places in the same class share broadly similar vegetation. That is why its classes carry names such as rainforest, savannah, desert, steppe and tundra.

What do the letters mean?

Reading a code is then mechanical. Cfb is temperate with no dry season and a warm summer; BWh is a hot desert; Dfc is a cold climate with no dry season and only one to three months above 10 °C.

• A, tropical: coldest month at 18 °C or above. Second letter f (rainforest, driest month at least 60 mm), m (monsoon) or w (savannah, with a dry season).
• B, arid: annual precipitation below a threshold that rises with mean annual temperature and depends on whether the rain falls mainly in summer or winter. W is desert, S is steppe; h (hot) or k (cold) depends on whether the mean annual temperature is at least 18 °C.
• C, temperate: warmest month above 10 °C and coldest month between 0 °C and 18 °C.
• D, cold: warmest month above 10 °C and coldest month at or below 0 °C.
• E, polar: warmest month at or below 10 °C; T (tundra) if the warmest month is above 0 °C, F (frost) if not.
• Second letter for C and D: s (dry summer), w (dry winter) or f (no dry season).
• Third letter for C and D: a (hot summer, warmest month at least 22 °C), b (warm summer, at least four months above 10 °C) or c (cold summer, one to three months above 10 °C); D climates can also be d (very cold winter, coldest month below −38 °C).

How are Köppen zones defined and mapped?

Because the classes are thresholds applied to climate averages, the result depends on the period and the data used. Beck et al. classify approximately 30-year periods, and a place close to a threshold can change class from one period or dataset to the next.

Versions also differ in detail. Beck et al. separate C from D at 0 °C in the coldest month, use a 70% rule to decide whether the rain falls mainly in summer or winter, and give the arid class B priority wherever it overlaps another class.

Widely used open maps at 1 km resolution are Version 2 by Beck et al. (2023), published in Scientific Data. They classify the world at 1 km for 1901–1930, 1931–1960, 1961–1990 and 1991–2020 from observation-based climatologies, and for 2041–2070 and 2071–2099 from downscaled, bias-corrected CMIP6 projections under seven SSP scenarios. Checked against weather-station observations, the maps classify 79.2% to 86.4% of stations correctly, and each map comes with confidence estimates.

How is climate change shifting Köppen zones?

Beck et al. estimate that about 5% of the global land surface, excluding Antarctica, moved to a different major class between 1901–1930 and 1991–2020. From 1991–2020 to 2071–2099 they project a further 5% under SSP1-2.6, 8% under SSP2-4.5 and 13% under SSP5-8.5.

Under SSP2-4.5 the largest transitions include about 2.8 million km² from temperate (C) to tropical (A), 2.6 million km² from polar (E) to cold (D), and 2.4 million km² from cold (D) to temperate (C). For a building expected to stand for 50 years or more, the class on the day of design may not be the one it spends most of its life in.

Why do architects use Köppen zones, and what are the limits?

Köppen codes are a fast, shared vocabulary. They tell a design team at a glance whether a site's main challenge is heat, cold, drought or seasonal rain, and they help find precedent buildings from similar climates elsewhere.

They are not a design tool on their own. The classification uses only monthly temperature and precipitation, so two sites with the same code can differ widely in humidity, wind, solar radiation and daily temperature swing, which drive comfort and energy use. US building energy codes use a different system, ANSI/ASHRAE Standard 169, based on degree days and moisture. Use Köppen to frame the climate, then look at the hourly data.

How C4B shows Köppen zones

C4B shows the Köppen-Geiger class of every location you search, next to its ASHRAE 169 climate zone and heating and cooling degree days at an 18.3 °C base. The climate zone map has a year slider from 1901 to 2100 across five scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5), based on Beck et al. (2023). A timeline shows the site's class at the building's completion, mid-life and end of life; projects save the building's own years.