Climate Classification

Climate classificationand climate classification is useful for characterizing the atmospheric environment, with the variables included depending on the classification’s purpose. Several classification systems have been devised, including Thornthwaite’s water-balance-based system, but the Köppen system has been employed frequently and will be used here. The three-letter abbreviation system for Köppen types has a capitalized first letter that describes the annual temperature regime, except for the “B” types described below. “A” (Tropical) climates are warm year-round with no cold season. “C” (or mesothermal or temperate)Temperate climates occur in subtropical to mid-latitude areas and have winters that can be cold but not continuously cold. “D” (or microthermal) climates also occur in mid-latitudes but have longer, harsher, uninterrupted winters, with summers that are not continuously hotEnergyin Arctic. “E” (or Arctic or Antarctic) climates are harsher than D climatesD climates (microthermal) and are unconducive to tree growth. B (Arid)Arid climates are dry, regardless of the annual temperature. “Dry” is determined by the extent to which potentialevapotranspiration evapotranspiration (PE)—the amount of evapotranspirationEnergyand evapotranspiration that could have occurred if water were freely available—exceeds its precipitation. The Köppen types are extended over the oceans here and in subsequent chapters to reveal truly global climatic types.