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How cold must the coldest month be for a Type D climate to receive the d designation?
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Köppen climate classification
The major climatic types are based on patterns of average precipitation, average temperature, and natural vegetation. This map depicts the world distribution of climate types based on the classification originally invented by Wladimir Köppen in 1900.
In the Köppen climate classification system, a Type D climate receives the d designation when the temperature of the coldest month is less than –38 °C. In such cases, the d designation is used in place of the a, b, or c subclasses.1