[[File:BS climate.png|thumb|upright=1.75|Regions with semi-arid climates
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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.
Defining attributes of semi-arid climates
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.
thumb|[[Sahel region of Mali.]]
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, semi-desert, 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. In South Asia, India and parts of Pakistan experience the seasonal effects of monsoons and feature short but well-defined wet seasons, but are not sufficiently wet overall to qualify as either a tropical savanna or a humid subtropical climate.
Hot semi-arid climates can be also found in parts of North America, such as most of northern Mexico, the ABC Islands, the rain shadows of Hispaniola's mountain ranges in the Dominican Republic and Haiti, parts of the Southwestern United States including California's Central Valley, and sections of South America such as the sertão, the Gran Chaco, and the poleward side of the arid deserts, where they typically feature a Mediterranean precipitation pattern, with generally rainless summers and wetter winters. They are also found in few areas of Europe surrounding the Mediterranean Basin. In Europe, BSh climates are predominantly found in southeastern Spain. It can also be found primarily in parts of south Greece but also in marginal areas of Thessaloniki and Chalkidiki in north Greece, most of Formentera, marginal areas of Ibiza
Charts of selected cities
Hot semi-arid
Cold semi-arid
See also
- Continental climate
- Dry climate
- Desert climate
- Dust Bowl (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 (a boundary marking the limit of semi-arid climates in the Australian state of South Australia)
- Köppen climate classification
- Palliser's Triangle (semi-arid area of Canada)
- Ustic (Soil Moisture Regime)
- Wave height