Semi-arid climate

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.

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 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 climates

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. 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.

Hot semi-arid climates are most commonly found in Africa, Australia, and South Asia. In Australia, a large portion of the Outback surrounding the central desert regions lies within the hot semi-arid climate region.[2] In South Asia, both 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, 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 primarily found in southeastern Spain,[3][4] various parts of south Greece,[5] [6] and marginal areas of Portugal and Cyprus.

Regions with 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 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.

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 subtropical climates, with dry summers, relatively wet winters, and even wetter springs and autumns.

Cold semi-arid climates are most commonly found in East Asia, the Middle East, including other parts of Asia, and Western North America. However, they can also be found in Northern Africa, South Africa, Europe (Central parts of Spain, Crimea, Greece, and North Macedonia), sections of South America and sections of interior southern Australia (e.g. Kalgoorlie and Mildura) and southern New Zealand (Alexandra).

• 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