Koeppen’s Scheme of World Climate Classification

How Koeppen Classifies Climate

Three Ways to Classify Climate

• Empirical classification groups climates using observed data, mainly temperature and precipitation. It does not ask why a climate behaves that way, only what the numbers show.
• Genetic classification groups climates by their causes instead, such as the air masses or wind belts that produce them.
• Applied classification is built for one specific purpose, such as farming or building design.
• V. Koeppen built the most widely used empirical scheme, in 1918. He linked specific temperature and precipitation values to the natural vegetation they support.

Koeppen’s Five Climate Groups

• A – Tropical. The coldest month still averages 18°C or higher. Capital letters A, C, D and E all mark humid climates.
• B – Dry. Potential evaporation exceeds precipitation here. B is the one group marking dry climates, not humid ones.
• C – Warm Temperate. The coldest month averages between -3°C and 18°C. These are the mid-latitude climates.
• D – Cold Snow Forest. The coldest month averages -3°C or below. This group only occurs in the Northern Hemisphere’s large land masses.
• E – Cold. Every month averages below 10°C. E climates sit at the highest latitudes.
• H – Highland. This climate is cold simply because of elevation, not latitude. It can appear at any latitude wherever mountains rise high enough.
• Small letters mark seasonality within each group. f means no dry season. m means a short monsoon-style dry season. w means a winter dry season. s means a summer dry season.
• Within Group B, S marks a steppe or semi-arid climate. W marks a true desert climate.

Climate Types Around the World

Tropical, Dry and Warm Temperate Climates

• Af – Tropical Wet. Found near the equator, in the Amazon Basin, western equatorial Africa and the East Indies islands. Rain falls almost every month.
• Am – Tropical Monsoon. Found across the Indian subcontinent, north-eastern South America and northern Australia, tied closely to the same mechanism behind the Indian Monsoon. Rain is heavy in summer, and winter stays dry.
• Aw – Tropical Wet and Dry. Found north and south of the Af zone, such as the Amazon forest’s fringes, Sudan and southern Central Africa. Rainfall is lower and more variable, with grassland vegetation.
• Dry climates span 15° to 60° latitude on both sides of the equator. Subtropical steppe and desert sit between 15° and 35°. Mid-latitude steppe and desert sit between 35° and 60°, mainly in continental interiors. Steppe (BS) gets just enough rain for sparse grassland, while true desert (BW) gets far less; the highest shade temperature ever recorded, 58°C, was measured at Al Aziziyah, Libya, in this subtropical desert zone.
• Cwa. Humid subtropical with a dry winter, found in the North Indian Plains and interior South China. It resembles Aw, except winters here stay warm instead of hot year-round. Its vegetation shifts accordingly, away from true tropical forest.
• Cs – Mediterranean. Found around the Mediterranean Sea and on west coasts near 30-40° latitude, such as Central California and Central Chile. Summers are hot and dry under a subtropical high. Winters are mild and rainy under the westerlies.
• Cfa – Humid Subtropical. Found on the eastern side of continents, like the southeastern United States and southern China, with rain all year round and hot summers near 27°C. Cfb – Marine West Coast. Sitting poleward of the Mediterranean zone on western coasts, moderated by the nearby ocean into small daily and yearly temperature swings.

Cold and Polar Climates

• Df and Dw. Cold snow-forest climates occur between 40° and 70° north latitude, across Europe, Asia and North America. Df has a humid winter. Dw, found mainly in north-eastern Asia, has a dry winter with a monsoon-like wind reversal.
• ET – Tundra. Found beyond 70° latitude, named for its low mosses, lichens and flowering plants. The subsoil stays permanently frozen as permafrost.
• EF – Ice Cap. Found over interior Greenland and Antarctica. Temperatures stay below freezing even in summer, and accumulated ice eventually breaks off as icebergs.
• H – Highland. Governed by elevation rather than latitude. Temperature and rainfall both change sharply over short distances, creating layered climate zones up a mountainside.

Beyond Classification: The Greenhouse Effect

• Gases in the atmosphere trap some outgoing heat and re-radiate it back down. Without this natural greenhouse effect, Earth’s surface would be about 33°C colder than it actually is.
• Carbon dioxide, methane, nitrous oxide and CFCs are the main greenhouse gases. Burning fossil fuels adds far more of them than natural sources alone, an “enhanced” version of the same effect that drives modern global warming.
• Koeppen’s climate types are not fixed forever. As global temperatures shift, the boundaries between his climate groups can shift too.