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 (BSh and BSk) 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):[citation needed]
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, semi-desert, or semi-arid climate).[1]
Furthermore, to delineate hot semi-arid climates from cold semi-arid climates, a mean annual temperature of 18 °C (64.4 °F) 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.
Regions with hot semi-arid climatesSemi-arid climate in Queensland, Australia.
Hot semi-arid climates (type "BSh") tend to be located from the high teens to mid-30s latitudes of the tropics and subtropics, typically in proximity to regions with a tropical savanna climate or a humid subtropical climate. These climates tend to have hot, or sometimes extremely hot, summers and warm to cool winters, with some to minimal precipitation. Hot semi-arid climates are most commonly found around the fringes of subtropical deserts.[citation needed]
Regions with cold semi-arid climatesSemi-arid climate in Montana, USA.
Cold semi-arid climates (type "BSk") tend to be located in elevated portions of temperate zones generally from the mid-30s to low 50s latitudes, typically bordering a humid continental climate or a Mediterranean climate. They are also typically found in continental interiors some distance from large bodies of water. Cold semi-arid climates usually feature warm to hot dry summers, though their summers are typically not quite as hot as those of hot semi-arid climates. Unlike hot semi-arid climates, areas with cold semi-arid climates tend to have cold and possibly freezing winters. These areas usually see some snowfall during the winter, though snowfall is much lower than at locations at similar latitudes with more humid climates.[citation needed]
Areas featuring cold semi-arid climates tend to have higher elevations than areas with hot semi-arid climates, and tend to feature major temperature swings between day and night, sometimes by as much as 20 °C (36 °F) or more. These large diurnal temperature variations are seldom seen in hot semi-arid climates. Cold semi-arid climates at higher latitudes tend to have dry winters and wetter summers, while cold semi-arid climates at lower latitudes tend to have precipitation patterns more akin to Mediterranean climates, with dry summers, relatively wet winters, and even wetter springs and autumns.[citation needed]
Cold semi-arid climates are most commonly found in central Asia and the western US, as well as the Middle East and other parts of Asia. However, they can also be found in Northern Africa, South Africa, sections of South America, sections of interior southern Australia (e.g. Kalgoorlie and Mildura) and southern New Zealand (Alexandra) and sections of Europe.[citation needed]
^Peel, M. C.; Finlayson, B. L.; McMahon, T. A. (March 1, 2007). "Updated world map of the Koppen-Geiger climate classification"(PDF). hydrol-earth-syst-sci.net. University of Melbourne: Hydrology and Earth System Sciences. pp. 1633–1644. Retrieved May 8, 2017.
^"Climate Atlas of Greece"(PDF). Hellenic National Meteorological Service. Archived from the original(PDF) on 21 September 2017. Retrieved 30 December 2019.
