- Rain shadow
"For the Australian television series see
Rain Shadow (TV series)."A rain shadow or rainshadow, or more accurately, precipitation shadow, is a dry region of land that is leewardof a mountain rangeor other geographic feature, with respect to prevailing winddirection. The mountains block the passage of rain-producing weather systems, casting a "shadow" of dryness behind them.
A rainshadow is warm and dry because as moist air masses rise to the top of a mountain range or large mountain, the air cools and it's temperature decreases until it reaches it's
dew point, the point at which the condenses as rain, and then falls either on the windwardside or atop the mountain. This is called " orographic liftingprecipitation". The effect of this phenomenon is the creation of an aridregion on the leeward side of the mountains. Also, the warm air absorbs moisture from the already dry and warm air (see Foehn winds). The land gets little precipitation because all the moisture is lost on the mountains. Furthermore, the warm air absorbs moisture from the already dry land.cite book|author=Whiteman, C. David|title=Mountain Meteorology: Fundamentals and Applications |publisher=Oxford University Press|year=2000|id=ISBN 0-19-513271-8]
Regions of notable rain shadow
There are regular patterns of
prevailing windsfound in bands round the Earth's equatorial region. The zone designated the trade windsis the zone between about 30° N. and 30° S., blowing predominantly from the northeast in the Northern Hemisphereand from the southeast in the Southern Hemisphere. The westerliesare the prevailing winds in the middle latitudesbetween 30 and 60 degrees latitude, blowing predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. The strongest westerly winds in the middle latitudes can come in the Roaring Fortiesbetween 30 and 50 degrees latitude.Fact|date=August 2007
Examples of notable rain shadowing include:
* The peaks of the
Caucasus Mountainsto the west, the Alborzmountains to the south and the ranges tied to the Himalayato the east rain shadow the Karakumand Kyzyl Kumdeserts east of the Caspian Sea.
Dasht-i-Lutin Iran is in the rain shadow of the Elburz and Zagros Mountainsand is one of the most lifeless areas on Earth.
* The Himalaya and connecting ranges also contribute to arid conditions in
Central Asiaincluding Mongolia's Gobidesert and China's Taklamakan Desert.
Ordos Desertis rain shadowed by mountain chains including the Kara-naryn-ula, the Sheitenula, and the In Shanmountains, which link on to the south end of the Great Khingan Mountains.
Great Indian Desertor Thar desert is bounded and rain shadowed by the Aravalliranges to the south-east, the Himalaya to the northeast, and the Kirthar and Sulaiman ranges to the west.
*Eastern Side of
Sahyadriranges on DeccanPlateau of India.
Atacama Desertin Chileis the driest desert on Earth because it is blocked from moisture on both sides (by the Andes mountainsto the east and high pressure over the Pacific at a latitude which keeps moisture from coming in from the west).
Patagoniais rain shadowed from the prevailing westerly winds by the Andesrange and is arid (e.g., in Santa Cruz few spots are capable of cultivation, the pastures being poor, water insufficient and salt lagoons fairly numerous).
Most rainshadows in the western
United Statesare due to mountain ranges, notably the Sierra Nevada and Cascades, [ USA Today. [http://www.usatoday.com/weather/tg/wrnshdw/wrnshdw.htm How mountains influence rainfall patterns.] Retrieved on 2008-02-29.] that intercept rain and snowfall that would otherwise reach a valley in the lee of the mid-latitude prevailing westerlies.
deserts of the Basin and Range Provincein the United Statesand Mexico, which includes the dry areas east of the Cascade Mountains of Oregonand Washington and the Great Basin, which covers almost all of Nevadaand parts of Utahare rain shadowed.
* The Mojave, Black Rock, Sonoran, and Chihuahuan deserts all are in regions which are rain shadowed.
* The aptly-named
Death Valleyin the United States, behind both the Pacific Coast Rangesof Californiaand the Sierra Nevada range, is one of the driest places on the planet.
Colorado Front Rangeis limited to the rainfall that makes it over the continental divide. While many places west of the divide receive as much as convert|40|in|mm of precipitation throughout the year, some places on the east side, notably Evergreen, Coloradoand Denver, Coloradoonly receive about 17-19 inches. Thus, the continental divideacts as a barrier for the precipitation. This effect only applies to west to east storms. When low pressure areas skirt the Rocky Mountainsto the south, they can give high precipitation to the east side and none to the west side. This happens rarely.
* The east slopes of the Coast Ranges in central and southern California also cut off the southern
San Joaquin Valleyfrom enough precipitation to ensure desert-like conditions in areas around Bakersfield.
* The eastern side of the
Coast Mountainsand the Cascade Rangein the province of British Columbia, Canadais a rain shadow. The Okanagan Valleywhich sits in this rain shadow is home to Osoyoos, Canada's only hot desert.
* The Dungeness Valley around
Sequim, Washingtonlies in the rain shadow of the Olympic Mountains. The area averages 10-15 inches of rain per year, less than half of the amount received in nearby Port Angelesand approximately 10% of that which falls in Forks on the western side of the mountains.
* The effect appears even in the eastern United States. Although much more humid than any obvious deserts or steppes, the
Shenandoah Valleymostly in western Virginia, lying between the Blue Ridge and the Appalachian Mountains, is drier than areas to the east and west because the modest mountains reduce rainfall within the valley. The lesser rainfall than that of surrounding areas makes this long valley paradoxically a richer agricultural area than rainier areas nearby. [ftp://ftp.ftw.nrcs.usda.gov/pub/prism/maps/va.pdf] [http://www.ocs.orst.edu/pub/maps/Precipitation/Total/States/WV/wv.gif]
Cantabrian Mountainsmake a sharp divide between " Green Spain" to the north and the dry central plateau. The northern-facing slopes receive heavy rainfall from the Bay of Biscay, but the southern slopes are in rain shadow. The most evident effect on the Iberian Peninsula occurs in the Almería, Murcia and Alicante areas, each with an average rainfall of 300 mm. and the dryest spot in Europe (see Cabo de Gata) mostly due to the mountainous range running through their western side which blocks the westerlies.
* Some valleys in the inner
Alpsare also strongly rainshadowed by the high surrounding mountains.
* The Plains of
Limagneand Forezin the northern Massif Central, France, are also relatively rainshadowed (mostly the plain of limagne, shadowed by the Chaîne des Puys(up to 2000mm of rain a year on the summits and below 600mm on Clermont-Ferrand, which is one of the dryest place in the country.
Athensis shielded strongly by mountains from the strong moisture-bearing winds of the Adriatic Seaand receives only a quarter the rainfall of most of Albania.
Skjåk, a municipality in Norway, lies in a deep valley and is rain shadowed such that it sees less annual precipitation than the Saharadesert.
* The windward side of the island of
Madagascar, which sees easterly on-shore winds, is wet tropical, while the western and southern sides of the island lie in the rain shadow of the central highlands and are home to thorn forests and deserts. The same is true for the island of Réunion.
*The formation of the
Atlas Mountainshas been deemed at least partially responsible for the climatic change which eventually created the Sahara. There is a strong rain shadow effect to the south side of the mountains.
New Caledonialies astride the Tropic of Capricorn, between 19° and 23° south latitude. The climate of the islands is tropical, and rainfall is brought by trade winds from the east. The western side of the Grande Terre lies in the rain shadow of the central mountains, and rainfall averages are significantly lower.
Hawaiialso has rain shadows, with some areas of the islands being desert, much to the surprise of many tourists. Orographic lifting produces the world's highest annual percipitation record, 12.7 meters (500 inches), on the island of Kauai; the leeward side is understandably rain shadowedcite book|author=Whiteman, C. David|title=Mountain Meteorology: Fundamentals and Applications |publisher=Oxford University Press|year=2000|id=ISBN 0-19-513271-8] . The entire island of Kahoolawelies in the rain shadow of Maui's East Maui Volcano.
New Zealandboasts one of the most remarkable rain shadows anywhere on Earth. On the South Island, the Southern Alps intercept moisture coming off the Tasman Sea. The mountain range is home to significant glaciers and 250 to convert|350|in|mm liquid water equivalent per year. To the east and down slope of the Southern Alps, scarcely convert|30|mi|km from the snowy peaks, yearly rainfall drops to less than convert|30|in|mm and some areas less than 15.
Tasmania, one of the states of Australia, the central Midlands region is in a strong rain shadow and receives only about a fifth as much rainfall as the highlands to the west.
New South Walesand Victoria (both states of Australia), the Monaro is shielded by both the Snowy Mountains to the northwest and coastal ranges to the southeast. Consequently, parts of it are as dry as the wheat-growing lands of those states.
:* [http://www.usatoday.com/weather/tg/wrnshdw/wrnshdw.htm USA Today on rain shadows] :* [http://www.weatherpages.com/rainshadow/ Weather pages on rain shadows]
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Look at other dictionaries:
rain shadow — /ˈreɪn ʃædoʊ/ (say rayn shadoh) noun a drier area to the lee of a mountain range in the path of rain bearing winds: *Billy lived out in the Dust, under the rain shadow; too dry for wheat, though it was said his father had tried it twice before he … Australian English dictionary
rain shadow — noun a relatively dry region sheltered from prevailing rain bearing winds by a range of hills … English new terms dictionary
rain shadow — noun Date: 1902 a region of reduced rainfall on the lee side of high mountains … New Collegiate Dictionary
rain shadow — a dry region on the lee side of a mountain range where rainfall is less and fish faunas may be depauperate … Dictionary of ichthyology
rain shadow — Meteorol. a region in the lee of mountains that receives less rainfall than the region windward of the mountains. [1900 05] * * * lee side of an orographic (mountainous) barrier, which receives considerably less precipitation than the… … Universalium
rain shadow — noun an area of diminished precipitation on the lee side of mountains … Wiktionary
rain shadow — noun an area that has little precipitation because some barrier causes the winds to lose their moisture before reaching it • Hypernyms: ↑area, ↑country … Useful english dictionary
Rain Shadow (TV series) — Infobox Television show name = Rain Shadow caption = show name 2 = genre = Drama creator = director = creative director = developer = presenter = starring = voices = narrated = theme music composer = opentheme = endtheme = composer = country =… … Wikipedia
Rain — is liquid precipitation. On Earth, it is the condensation of atmospheric water vapor into drops heavy enough to fall, often making it to the surface. Rain is the primary source of fresh water for most areas of the world, providing suitable… … Wikipedia
Shadow — A shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two dimensional silhouette … Wikipedia