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[[Image:Koppen_classification_worldmap_BW.png|thumb|415px|Locations of arid climates. BWn is sorted into either BWk or BWh.]]

Under the [[Koppen climate classification]], a '''desert climate''' (''BWh'', ''BWk'', ''BWn''), also known as an '''arid climate''', is a climate that does not meet the criteria to be classified as a [[polar climate]], and in which [[Precipitation (meteorology)|precipitation]] is too low to sustain any vegetation at all, or at most a very scanty scrub. An area that features this climate usually (but not always) experiences less than 250 mm (10 inches) per year of precipitation and in some years may experience no precipitation at all. In some instances an area may experience more than 250 mm of precipitation annually, but is still considered a desert climate because the region loses more water via [[evapotranspiration]] than falls as precipitation ([[Tucson, Arizona]] and [[Alice Springs, Northern Territory]] are examples of this). There are usually two or three variations of a desert climate: a hot desert climate (''BWh''), a cold desert climate (''BWk'') and, sometimes, a mild desert climate (''BWn''). Furthermore, to delineate "hot desert climates" from "cold desert climates", there are three widely used [[isotherm]]s: Either a mean annual temperature of 18°C, or a mean temperature of 0°C or -3°C in the coldest month, so that a location with a "BS" type climate with the appropriate temperature above whichever isotherm is being used is classified as "hot semi-arid" (BWh), and a location with the appropriate temperature below the given isotherm is classified as "cold semi-arid" (BWk).

To determine if a location has an arid climate, the precipitation threshold must first be determined. Finding the precipitation threshold (in millimeters) involves first multiplying the average annual temperature in °C by 20, then adding 280 if 70% or more of the total precipitation is in the high-sun half of the year (April through September in the Northern Hemisphere, or October through March in the Southern), or 140 if 30%–70% of the total precipitation is received during the applicable period, or 0 if less than 30% of the total precipitation is so received. If the area's annual precipitation is less than half the threshold, it is classified as a ''BW'' ('''desert climate'''). [http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf]

==Hot desert climates==
[[Image:Koppen classification worldmap BWh.png|thumb|left|250px|Regions with hot desert climates]]
Hot desert climates are typically found under the [[subtropical ridge]] where there is largely unbroken sunshine for the whole year due to the stable descending air and high pressure. Such areas include the [[Sahara]], the [[Arabian Desert|Arabian]], [[Syrian Desert|Syrian]] and [[Kalahari Desert]]s, large parts of [[Iran]], northwest [[India]], the southwestern [[United States]], Northern [[Mexico]], and much of [[Australia]]. Two small islands in Europe have a hot desert climate; namely the [[Greece|Greek]] islands of [[Anafi]] and [[Santorini]].<ref>http://www.hydrol-earth-syst-sci.net/11/1633/2007/hess-11-1633-2007.pdf</ref>

In many locations featuring a hot desert climate, maximum temperatures of 40°C to 45°C are not uncommon in summer. During colder periods of the year, night-time temperatures can drop to freezing or below due to the exceptional radiation loss under the clear skies. However, very rarely do temperatures drop far below freezing.

===Notable cities with a hot desert climate===
{| width="100%"
|- valign=top
| width=50% |
*[[Cairo]], [[Egypt]]
*[[Khartoum]], [[Sudan]]
*[[Nouakchott]], [[Mauritania]]
*[[Djibouti City]], [[Djibouti]]
*[[Riyadh]], [[Saudi Arabia]]
*[[Desertas Islands]], [[Portugal]]
*[[Jeddah]], [[Saudi Arabia]]
*[[Dammam]], [[Saudi Arabia]]
*[[Amareleja]], [[Portugal]]
*[[Kuwait City]], [[Kuwait]]
*[[Dubai]], [[UAE]]
*[[Abu Dhabi]], [[UAE]]
*[[Baghdad]], [[Iraq]]
*[[Manama]], [[Bahrain]]
*[[Doha]], [[Qatar]]
| width=50% |
*[[Muscat, Oman|Muscat]], [[Oman]]
*[[Karachi]], [[Pakistan]]
*[[Faisalabad]], [[Pakistan]]
*[[Jodhpur]], [[India]]
*[[Ashgabat]], [[Turkmenistan]]
*[[Eilat]], [[Israel]]
*[[Alice Springs]], [[Australia]]
*[[Broken Hill]], [[Australia]]
*[[Ciudad Juárez]], [[Mexico]]
*[[Hermosillo]], [[Mexico]]
*[[Mexicali]], [[Mexico]]
*[[Phoenix, Arizona|Phoenix]], [[USA]]
*[[Las Vegas, Nevada|Las Vegas]], [[USA]]
*[[El Paso, Texas|El Paso]], [[USA]]
|
|}

==Cold desert climates==
[[Image:Koppen classification worldmap BWk.png|thumb|left|250px|Regions with cold desert climates]]
[[Image:WheelerSnow.JPG|thumb|Cold deserts do get the occasional blanket of snow, like [[Snake Valley (Great Basin)|Snake Valley]], Utah and Nevada]]
This variant of the desert climate is somewhat rare outside of Asia. A cold desert climate is typically found in [[temperate]] zones, almost always in the [[rain shadow]] of high mountains which restrict precipitation from the westerly winds, or in the case of Central Asia, from the [[monsoon]]. The [[Gobi desert]] in Mongolia is a classic example of a region with a cold desert climate. Though hot in summer, it shares the very cold winters of the rest of Central Asia. The [[Kyzyl Kum]] and [[Taklamakan Desert|Taklamakan]] deserts of [[Central Asia]] and the drier portions of the [[Great Basin Desert]] of the western [[United States]] are other major examples of '''BWk''' climates.

Cold desert climates can feature hot (sometimes exceptionally hot) and dry summers, though summers typically are not quite as hot as summers in hot desert climates. Unlike hot desert climates, cold desert climates usually feature cold, sometimes brutally cold, dry winters with temperatures far below the freezing point. Cold deserts are typically found at higher altitudes than hot desert climates, and are usually drier than hot desert climates.

Arctic and Antarctic regions also receive very little precipitation during the year, owing to the exceptionally cold dry air, but they are generally classified as having [[polar climate]]s.

===Notable cities with a cold desert climate===
*[[Kashgar]], [[People's Republic of China|China]]
*[[Kumul, Xinjiang|Kumul]], [[People's Republic of China|China]]
*[[Golmud]], [[People's Republic of China|China]]
*[[Leh]], [[India]]
*[[Khovd (city)|Khovd]], [[Mongolia]]

==Mild desert climates==
This variant of a desert climate is extremely rare. Mild desert climates are usually found along the west coasts of continents at tropical or near-tropical locations, or at high altitudes in areas that would otherwise feature hot desert climates.

Mild desert climates are characterized by more moderate temperatures than encountered elsewhere at comparable latitudes (usually due to the nearby presence of cold ocean currents) and, in the case of coastal mild deserts, frequent fog and low clouds, despite the fact that these places can rank among the driest on Earth in terms of actual precipitation received. Temperatures are mild throughout the year, usually not subject to any of the temperature extremes typically found in desert climates. Some publications do not have a "mild desert" category; in these documents mild desert climates are sorted into either the hot desert or cold desert classifications.

===Notable cities with a mild desert climate===
*[[Lima, Peru]]
*[[Sanaa, Yemen]]
*[[Walvis Bay]], [[Namibia]]

==Regions of varying classification==
As stated previously, there are three isotherms used to delineate between hot and cold desert climates. As a result of this, some areas can have climates that are classified as hot or cold depending on the isotherm used. Such locations include:
*[[Mendoza, Argentina]]
*[[Baku]], [[Azerbaijan]]
*[[Quetta]], [[Pakistan]]
*[[Albuquerque, New Mexico|Albuquerque]], [[USA]]
*[[St. George, Utah|St. George]], [[USA]]

==Charts of Selected Cities==
===Hot Desert Climates===
{{climate chart
| [[Baghdad]]
| 3.8 | 15.5 | 27.2
| 5.5 | 18.5 | 19.2
| 9.6 | 23.6 | 22.0
| 15.2 | 29.9 | 15.6
| 20.1 | 36.5 | 3.2
| 23.3 | 41.3 | 0
| 25.5 | 44.0 | 0
| 24.5 | 43.5 | 0
| 20.7 | 40.2 | 0
| 15.9 | 33.4 | 3.3
| 9.2 | 23.7 | 12.4
| 5.1 | 17.2 | 20.0
|clear = both
|float = left
|source = [http://worldweather.wmo.int/154/c01464.htm WMO] }}

{{climate chart
|[[Riyadh]]
| 9.0 | 20.2 | 11.7
| 11.0 | 23.0 | 8.5
| 15.0 | 27.3 | 24.7
| 20.3 | 33.3 | 22.3
| 25.7 | 39.1 | 4.6
| 27.6 | 42.4 | 0
| 29.1 | 43.5 | 0
| 28.8 | 43.2 | 0.2
| 25.7 | 40.3 | 0
| 20.9 | 35.0 | 1.7
| 15.4 | 27.7 | 7.9
| 10.6 | 22.0 | 13.0
|source=[http://www.pme.gov.sa/Riyadh%20Old.htm]
|float=left
|clear=none
}}

{{climate chart
| [[Phoenix, Arizona|Phoenix]]
| 7.1 | 19.6 | 21.1
| 9.1 | 21.9 | 19.6
| 11.7 | 24.5 | 27.2
| 14.2 | 29.3 | 6.4
| 19.7 | 34.4 | 4.1
| 24.2 | 39.9 | 2.3
| 28.3 | 41.4 | 25.1
| 27.6 | 40.3 | 23.9
| 24.2 | 37.2 | 19.0
| 16.7 | 30.9 | 20.1
| 10.2 | 23.9 | 18.5
| 6.6 | 19.5 | 23.4
|source= [http://www.wrcc.dri.edu/cgi-bin/cliNORMNCDC2000.pl?azphoe WRCC]
|float=left
|clear=none
}}

{{climate chart
| [[Khartoum]]
| 15.6 | 30.8 | 0
| 17.0 | 33.0 | 0
| 20.5 | 36.8 | 0
| 23.6 | 40.1 | 0
| 27.1 | 41.9 | 0.4
| 27.3 | 41.3 | 4.0
| 25.9 | 38.4 | 46.3
| 25.3 | 37.3 | 75.2
| 26.0 | 39.1 | 25.4
| 25.5 | 39.3 | 4.8
| 21.0 | 35.2 | 0.7
| 17.1 | 31.8 | 0
|source= [http://worldweather.wmo.int/085/c00249.htm WMO]
|float=left
|clear=none }}

{{climate chart
|[[Mexicali]]
|5|21|13.0
|7|24|9.1
|9|26|7.9
|12|30|1.3
|16|34|0.8
|20|39|0.3
|24|42|1.5
|25|41|8.1
|22|38|9.1
|15|33|8.9
|8|26|4.6
|5|21|10.9
|source=[http://www.weather.com/outlook/travel/businesstraveler/wxclimatology/monthly/graph/MXBC0004?from=36hr_bottomnav_business]
|float=left
|clear=none
}}

{{climate chart
|[[Hermosillo]]
|9|24|10
|11|26|9
|15|28|3
|18|32|1
|21|36|1
|23|40|2
|28|42|50
|28|41|53
|24|37|30
|19|34|11
|13|28|8
|10|25|14
|source=[http://www.weather.com/outlook/travel/businesstraveler/local/MXSR0091?lswe=hermosillo&from=searchbox_localwx]
|float=left
|clear=none
}}

{{climate chart
| [[Ashgabat]]
| -1.6 | 7.4 | 22
| -0.2 | 9.6 | 27
| 4.9 | 15.6 | 39
| 11.1 | 24.1 | 44
| 16.2 | 30.0 | 28
| 20.7 | 35.7 | 4
| 23.1 | 38.2 | 3
| 20.5 | 36.6 | 1
| 15.4 | 31.5 | 4
| 9.1 | 23.2 | 14
| 4.6 | 16.6 | 20
| 0.7 | 9.8 | 21
|float=left
|clear=none
|source=[http://www.worldweather.org/111/c00212.htm WMO] }}

{{clear}}

===Cold Desert Climates===
{{climate chart
| [[Kashgar]]
| -10.2 | 0.3 | 2.1
| - 6.2 | 5.1 | 5.7
| 1.7 | 13.5 | 6.7
| 8.6 | 22.2 | 5.2
| 12.9 | 26.4 | 8.5
| 16.1 | 30.2 | 7.7
| 18.6 | 32.1 | 9.1
| 17.2 | 30.7 | 7.9
| 11.9 | 26.5 | 5.3
| 4.7 | 19.8 | 2.5
| - 1.9 | 10.6 | 1.6
| - 7.7 | 1.9 | 1.7
| float=left
| clear=none
| source= [http://cdc.cma.gov.cn/shuju/search1.jsp?dsid=SURF_CLI_CHN_MUL_MMON_19712000_CES&tpcat=SURF&type=table&pageid=3 China Meteorological Administration] }}
{{climate chart
| [[Turpan]]
| -12.1 | -2.3 | 1.1
| - 6.0 | 6.0 | 0.5
| 3.2 | 16.3 | 1.2
| 12.4 | 26.5 | 0.5
| 18.7 | 33.3 | 0.9
| 23.2 | 37.9 | 2.9
| 25.0 | 39.6 | 1.9
| 22.8 | 38.0 | 1.8
| 16.3 | 31.9 | 1.6
| 7.1 | 21.8 | 1.7
| - 2.1 | 9.5 | 0.6
| - 9.6 | -0.8 | 1.0
| float=left
| clear=none
| source= [http://cdc.cma.gov.cn/shuju/search1.jsp?dsid=SURF_CLI_CHN_MUL_MMON_19712000_CES&tpcat=SURF&type=table&pageid=3 China Meteorological Administration] }}

{{clear}}

===Mild Desert Climates===
{{climate chart
|[[Lima]]
|20|26|0
|20|26|0
|20|26|0
|18|24|0
|17|22|0
|16|20|2.5
|15|19|5
|15|18|2.5
|15|19|2.5
|16|20|2.5
|17|22|0
|18|24|0
|source=[http://www.weatherbase.com/weather/weather.php3?s=82648&refer=&units=metric]
|float=left
|clear=none
}}

{{clear}}

==References==
{{reflist}}


==External links==
*[http://www.ace.mmu.ac.uk/eae/Climate/Older/Desert_Climate.html Desert climate summary]
*[http://www.blueplanetbiomes.org/desert.htm Desert report/essay]

{{Koppen}}

[[Category:Climate]]
[[Category:Deserts]]
[[Category:Köppen climate classifications]]
[[Category:Climate of Africa]]
[[Category:Climate of Asia]]
[[Category:Climate of Australia]]
[[Category:Climate of Europe]]
[[Category:Climate of North America]]
[[Category:Climate of South America]]
[[Category:Desert flora| ]]
[[Category:Deserts and xeric shrublands|+Climate]]

[[he:אקלים צחיח]]
[[ms:Iklim gurun]]
[[pt:Clima desértico]]
[[sr:Пустињска клима]]
[[fi:Aavikkoilmasto]]
[[tr:Çöl iklimi]]

Revision as of 15:00, 13 December 2010

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