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Concept
Climat semi-aride
Résumé
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different biomes.
A more precise definition is given by the Köppen climate classification, which treats steppe climates (BSk and BSh) as intermediates between desert climates (BW) and humid climates (A, C, D) in ecological characteristics and agricultural potential. Semi-arid climates tend to support short, thorny or scrubby vegetation and are usually dominated by either grasses or shrubs as they usually cannot support forests.
To determine if a location has a semi-arid climate, the precipitation threshold must first be determined. The method used to find the precipitation threshold (in millimeters):
multiply by 20 the average annual temperature in degrees Celsius and then
add 280 if at least 70% of the total precipitation falls in the summer half of the year (April–September in the northern hemisphere, October–March in the southern hemisphere)
add 140 if 30–70% of the total precipitation falls in the summer half of the year
add nothing if less than 30% of the total precipitation falls in the summer half of the year
If the area's annual precipitation in millimeters is less than the threshold but more than half or 50% the threshold, it is classified as a BS (steppe or semi-arid climate).
Furthermore, to delineate hot semi-arid climates from cold semi-arid climates, a mean annual temperature of is used as an isotherm. A location with a BS-type climate is classified as hot semi-arid (BSh) if its mean temperature is above this isotherm, and cold semi-arid (BSk) if not.
Hot semi-arid climates (type "BSh") tend to be located in the 20s and 30s latitudes of the tropics and subtropics, typically in proximity to regions with a tropical savanna, Mediterranean, and hot desert climates.
Source officielle
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