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semiarid climate
A semi-arid climate or steppe climate is the climate of a region that receives precipitation below potential evapotranspiration, but not extremely. A more precise definition is given by the Köppen climate classification that treats steppe climates (''BSk'' and ''BSh'') as intermediates between desert climates (BW) and humid climates in ecological characteristics and agricultural potential. Semi-arid climates tend to support short or scrubby vegetation, with semi-arid areas usually dominated by either grasses or shrubs.
To determine if a location has a semi-arid climate, the precipitation threshold must first be determined. Finding the precipitation threshold (in millimeters) involves first multiplying the average annual temperature in °C by 20, then adding 280 if 70% or more of the total precipitation is in the high-sun half of the year (April through September in the Northern Hemisphere, or October through March in the Southern), or 140 if 30%–70% of the total precipitation is received during the applicable period, or 0 if less than 30% of the total precipitation is so received. If the area's annual precipitation is less than the threshold but more than half the threshold, it is classified as a ''BS'' (steppe climate).
Furthermore, to delineate "hot semi-arid climates" from "cold semi-arid climates", there are three widely used isotherms: Either a mean annual temperature of 18°C, or a mean temperature of 0°C or −3°C in the coldest month, so that a location with a "BS" type climate with the appropriate temperature above whichever isotherm is being used is classified as "hot semi-arid" (BSh), and a location with the appropriate temperature below the given isotherm is classified as "cold semi-arid" (BSk).
==Hot semi-arid climates==
Hot semi-arid climates (type "BSh") tend to be located in the tropics and subtropics. These climates tend to have hot, sometimes extremely hot, summers and mild to warm winters. Snow rarely (if ever) falls in these regions. Hot semi-arid climates are most commonly found around the fringes of subtropical deserts. The most common variant of a hot semi-arid climate, found in regions such as West Africa, India, parts of Mexico and bordering areas in Texas, parts of Southern California, and small parts of Pakistan experiences the seasonal effects of monsoons and has a short but well-defined wet season, but is not sufficiently wet overall to qualify as a tropical savanna climate. In Australia, a large portion of the Outback surrounding the central desert regions, lies within the hot semi-arid climate regime.〔(Bureau of Meteorology - CDlimate classification maps )〕 Hot semi-arid climates can also be found in sections of South America such as the ''sertão'' and on the poleward side of the arid deserts where they typically feature a Mediterranean precipitation pattern, with generally rainless summers and wetter winters.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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