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Arid regions of the Western United States as mapped in 1893. Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.
If the annual precipitation is less than 50% of this threshold, the classification is BW (arid: desert climate); if it is in the range of 50%–100% of the threshold, the classification is BS (semi-arid: steppe climate). [9] [11] A third letter can be included to indicate temperature.
The desert climate or arid climate (in the Köppen climate classification BWh and BWk) is a dry climate sub-type in which there is a severe excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in desert climates are dry and hold little moisture, quickly evaporating the already little rainfall they receive.
Climate classifications are systems that categorize the world's climates. A climate classification may correlate closely with a biome classification, as climate is a major influence on life in a region. The most used is the Köppen climate classification scheme first developed in 1884. [1] [2]
Today, the most commonly used climate map is the Köppen climate classification, developed by Russian climatologist of German descent and amateur botanist Wladimir Köppen (1846–1940), which divides the world into five major climate regions, based on average annual precipitation, average monthly precipitation, and average monthly temperature.
Aridification is the process of a region becoming increasingly arid, or dry.It refers to long term change, [1] rather than seasonal variation. It is often measured as the reduction of average soil moisture content.
Semi-arid lands; Arid lands; Hyper-arid lands; Some authorities regard hyper-arid lands as deserts (United Nations Convention to Combat Desertification - UNCCD) although a number of the world's deserts include both hyper-arid and arid climate zones. The UNCCD excludes hyper-arid zones from its definition of drylands.
The Köppen climate classification is the most widely used climate classification system. [2] It defines a tropical climate as a region where the mean temperature of the coldest month is greater than or equal to 18 °C (64 °F) and does not fit into the criteria for B-group climates, classifying them as an A-group (tropical climate group). [3]