semi-arid region
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A semi-arid climate, semi-desert climate, or steppe climate is a
dry climate A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and morphogenesis, development of plant and animal life. Regions with arid climates tend to lack vegetation and are called Deserts and ...
sub-type. It is located on regions that receive
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
below
potential evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpira ...
, but not as low as a
desert climate 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 deser ...
. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different
biome A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...
s.


Defining attributes of semi-arid climates

A more precise definition is given by the
Köppen climate classification The Köppen climate classification is one of the most widely used climate classification systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notabl ...
, which treats steppe climates (''BSk'' and ''BSh'') as intermediates between
desert climate 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 deser ...
s (BW) and humid climates (A, C, D) in
ecological Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps wi ...
characteristics and agricultural potential. Semi-arid climates tend to support short, thorny or scrubby vegetation and are usually dominated by either
grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns a ...
es or shrubs as it usually can't 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, there are three widely used isotherms: either a mean annual temperature of , a mean temperature of in the coldest month, or a mean temperature of in the coldest month. A location with a ''BS''-type climate is classified as hot semi-arid (''BSh'') if its appropriate mean temperature is above whichever isotherm is being used, and a location with 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 20s and 30s latitudes of the
tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referr ...
and subtropics, typically in proximity to regions with a
tropical savanna Tropical and subtropical grasslands, savannas, and shrublands is a terrestrial biome defined by the World Wide Fund for Nature. The biome is dominated by grass and/or shrubs located in semi-arid to semi-humid climate regions of subtropical and t ...
or a humid subtropical climate. These climates tend to have hot, 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. Hot semi-arid climates are most commonly found in
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, Australia and
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. In Australia, a large portion of the Outback surrounding the central desert regions lies within the hot semi-arid climate region.Bureau of Meteorology – climate classification maps
/ref> In South Asia, both
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and sections of
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experience the seasonal effects of
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal osci ...
s and feature short but well-defined
wet season The wet season (sometimes called the Rainy season) is the time of year when most of a region's average annual rainfall occurs. It is the time of year where the majority of a country's or region's annual precipitation occurs. Generally, the sea ...
s, but are not sufficiently wet overall to qualify as a
tropical savanna climate Tropical savanna climate or tropical wet and dry climate is a tropical climate sub-type that corresponds to the Köppen climate classification categories ''Aw'' (for a dry winter) and ''As'' (for a dry summer). The driest month has less than of p ...
. Hot semi-arid climates can also be found in
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, primarily in southeast
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
http://www.aemet.es/documentos/es/conocermas/recursos_en_linea/publicaciones_y_estudios/publicaciones/2Atlas_climatologico/Atlas_Clima_Macaronesia___Baja.pdf and parts of
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,
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
,
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
and
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. They are also found in parts of North America, such as most of northern
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, the ABC Islands, the rain shadows of Hispaniola's mountain ranges in the
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and Haiti, most of the Southwestern United States, and sections of
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such as the ''
sertão The ''sertão'' (, plural ''sertões'') is the "hinterland" or "backcountry". In Brazil, it refers both to one of the four sub-regions of the Northeast Region of Brazil (similar to the specific association of " outback" with Australia in Englis ...
'', the
Gran Chaco The Gran Chaco or Dry Chaco is a sparsely populated, hot and semiarid lowland natural region of the Río de la Plata basin, divided among eastern Bolivia, western Paraguay, northern Argentina, and a portion of the Brazilian states of Mato ...
, and the poleward side of the arid deserts, where they typically feature a
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...
precipitation pattern, with generally rainless summers and wetter winters.


Cold semi-arid climates

Cold semi-arid climates (type "BSk") tend to be located in elevated portions of temperate zones, typically bordering a
humid continental climate A humid continental climate is a climatic region defined by Russo-German climatologist Wladimir Köppen in 1900, typified by four distinct seasons and large seasonal temperature differences, with warm to hot (and often humid) summers and freezing ...
or a
Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...
. 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. 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 variation In meteorology, diurnal temperature variation is the variation between a high air temperature and a low temperature that occurs during the same day. Temperature lag Temperature lag is an important factor in diurnal temperature variation: peak da ...
s 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 subtropical climates, with dry summers, relatively wet winters, and even wetter springs and autumns. Cold semi-arid climates are most commonly found in
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, the
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and other parts of Asia and Western North America. However, they can also be found in Northern Africa, South Africa, Europe, sections of South America and sections of interior southern Australia (e.g. Kalgoorlie and
Mildura Mildura is a regional city in north-west Victoria, Australia. Located on the Victorian side of the Murray River, Mildura had a population of 34,565 in 2021. When nearby Wentworth, Irymple, Nichols Point and Merbein are included, the area h ...
) and New Zealand (around Alexandra).


Regions of varying classification

In climate classification, any one of three isotherms may be used to delineate hot from cold semi-arid climates — that of average annual temperature; or that of the coldest month, either or . The warm side of the isotherm of choice is classified as BSh, the cooler side as BSk. As a result of these differing definitions, some areas can have climates that are classified as either hot or cold semi-arid, depending on the isotherm used. One such location is
San Diego, California San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the eighth most populous city in the United Stat ...
(at its main airport). The city has cool summers for its latitude, due to prevailing winds off the ocean, so the average annual temperature is below ); however, winters are mild, with an average January temperature of , much closer to the coldest-month isotherm that separates tropical and subtropical climates than to the coldest-month isotherm that separates temperate and continental climates.


Charts of selected cities


See also

* Continental climate *
Dry climate A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and morphogenesis, development of plant and animal life. Regions with arid climates tend to lack vegetation and are called Deserts and ...
*
Desert climate 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 deser ...
*
Dust Bowl The Dust Bowl was a period of severe dust storms that greatly damaged the ecology and agriculture of the American and Canadian prairies during the 1930s. The phenomenon was caused by a combination of both natural factors (severe drought) a ...
(an era of devastating dust storms, mostly in the 1930s, in semi-arid areas on the Great Plains of the United States and Prairies of Canada) *
Goyder's Line Goyder's Line is a line that runs roughly east–west across South Australia and, in effect, joins places with an average annual rainfall of . North of Goyder's Line, annual rainfall is usually too low to support cropping, with the land being sui ...
(a boundary marking the limit of semi-arid climates in the Australian state of South Australia) *
Köppen climate classification The Köppen climate classification is one of the most widely used climate classification systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notabl ...
*
Palliser's Triangle Palliser's Triangle, or the Palliser Triangle, is a semi-arid steppe occupying a substantial portion of the Western Canadian Prairie Provinces, Saskatchewan, Alberta and Manitoba, within the Great Plains region. While initially determined to be un ...
(semi-arid area of Canada) * Ustic (Soil Moisture Regime) *
Wave height In fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighboring trough. ''Wave height'' is a term used by mariners, as well as in coastal, ocean and naval engineering. At sea, the te ...


References


External links

{{Koppen Grasslands Köppen climate types Plains Prairies