Koeppen's classification of world climates

The boundary between C and D climates is determined mainly by winter severity, represented by the mean temperature of the coldest month. C climates have milder winters, while D climates have colder winters under the standard Köppen criteria. Rainfall, distance from the sea, and pressure range are not the defining criterion.

Cfa and Cfb share the first two symbols: C means warm temperate and f means no dry season. Their difference is the third symbol. In Cfa, a indicates a hot summer with the warmest month at or above 22°C; in Cfb, b indicates a warm or moderate summer with the warmest month below 22°C. Therefore A is correct.

Dfc belongs to the cold continental or subarctic group. D indicates a snow or continental climate, f means there is no pronounced dry season, and c describes a short, cool summer: at least one month is above 10°C, but fewer than four months reach 10°C. Thus option A gives the most accurate meaning.

In both Dwa and Dfa, D identifies a cold continental climate and a indicates a hot summer. The second symbol expresses precipitation seasonality: w means a dry winter, whereas f means no pronounced dry season, with adequate moisture throughout the year. Consequently, option A correctly distinguishes Dwa from Dfa.

Both ET and EF are polar climates, so the decisive measure is the mean temperature of the warmest month. ET, or tundra climate, has a warmest month above 0°C but below 10°C. EF, or ice-cap climate, has every month, including the warmest, below 0°C. Thus option A states the relevant limit.

Köppen classification is based mainly on temperature and precipitation, but altitude can substantially modify both. Air temperature generally decreases with elevation, and mountains can create orographic rainfall and local rain shadows. Therefore a highland climate may not fit the surrounding lowland latitude pattern and should be interpreted cautiously.

Köppen linked climate zones with natural vegetation because temperature and precipitation are the major environmental controls on plant growth, distribution, and structure. His boundaries were designed partly with observable vegetation patterns in mind. Soil colour, ocean currents alone, and population density are not the basis of this climatic classification.

As denotes a tropical climate with a dry summer. Many tropical regions are influenced by seasonal circulation patterns that produce a dry winter and wetter summer, represented by Aw, or a short dry season, represented by Am. A genuinely dry tropical summer is less common, so As is relatively rare.

Köppen's B group represents dry climates. When precipitation is less than half of the calculated aridity threshold, the climate is classified as BW, meaning desert or hyper-arid. If precipitation is more than half but still below the full threshold, it is BS, meaning steppe or semi-arid. Therefore B is correct.

A B climate is classified as BS when precipitation is insufficient to meet the full aridity threshold but exceeds half of that threshold. BS means steppe or semi-arid climate. BW is reserved for conditions in which precipitation is below half the threshold, making the climate more intensely dry and desert-like.

The Sahara has extremely low and unreliable precipitation, placing it in the BW desert group. Its generally high mean annual temperature gives the final letter h, meaning hot. Therefore BWh describes a hot desert climate. The code does not indicate tundra, humid oceanic conditions, or a rainforest.

The Gobi is an arid desert, so it belongs to the BW group. Unlike hot deserts such as the Sahara, its high continental location and latitude produce a low mean annual temperature and very cold winters. The final letter k therefore identifies it as a cold-desert subtype rather than BWh.

In Köppen’s extended notation for D climates, the final letter d denotes an extremely severe winter. It is associated with very low temperatures during the coldest month, colder than the condition represented by the ordinary f, w, or s seasonal symbols. Thus, Dfd and Dwd describe continental climates with severe winter conditions, not dry summers or tropical rainfall.