Arid zone

Japanese: 乾燥帯 - かんそうたい（英語表記）arid zone

Generally, it refers to an area where the annual precipitation is less than the annual evaporation, but evaporation is difficult to measure, and in many areas it is impossible to directly compare the two measured values. Therefore, various definitions have been proposed for where the boundary between arid and humid areas should be. All of them use temperature instead of evaporation to represent the thermal environment, express the degree of aridity as a ratio to precipitation, which indicates the water environment, and determine the boundary based on the distribution of vegetation on the planet. For example, E. de Martonne defined the aridity index I as P / ( T + 10) (where P is precipitation and T is temperature (℃)), setting the boundary between humid open ocean areas and dry inland areas at 10, and defining areas below 10 as arid zones.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

一般に年降水量が年蒸発量より少ない地域をいうが，蒸発量の観測が難しく，両者を直接実測値で比べることは多くの地域で不可能である。そこで，乾燥地域と湿潤地域の境界線をどこにするか，さまざまな定義が提出されている。いずれも蒸発量の代りに熱環境を表すものとして気温も用い，水環境を示す降水量との比で乾燥の度合を表現し，地球上の植生分布などから境界を定めている。たとえば，マルトンヌE.de Martonneは乾燥示数IをP/(T＋10)(ここでPは降水量，Tは気温(℃))と定義し，湿潤な外洋地域と乾燥した内陸地域との境界を10とし，10以下の地域を乾燥帯とした。

出典　株式会社平凡社世界大百科事典第２版について　情報

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