EPOW - Ecology Picture of the Week

Back of the Rain Shadow

Transverse Mountain Range
Southern California, USA

Explanation:  Below us is a beautiful example of the rain shadow effect, whereby high mountains block moisture-laden air, forming an arid environment with scant rainfall.  

This week we are flying north along the Transverse Mountain Range of southern California -- more specifically, the San Bernadino Mountains.  To the left (the west) is a low fog overcast coming in from off the Pacific coast and filling the Los Angeles Basin ... but it is neatly blocked by the San Bernadinos so that virtually none of this moisture gets to the east side to the arid interior of Lucerne and Apple Valleys.   

Rain shadows are found in many parts of the world where linear mountain ranges block moist prevailing winds.  Here is another outstanding example I photographed on the arid southeastern "back" side of Mount Kenya in Kenya, east Africa:

The long ridgeline on the horizon is actually Mount Kenya of east Africa.
Moisture-laden storm clouds from the humid north and west are quite blocked,
leaving this side in arid scrub and grasslands.  

The result is the formation of montane rainforests on the upper slopes of the 
mountain that harbor many unique forms of life, such as endemic land 
snails (see Tattersfield et al. 2001) .

On a sub-continental scale, rain shadows can result in the formation of arid grasslands such as the Great Basin prairies of the American interior West, and even the driest place on Earth in the form of the Atacama Desert of northern Chile.

Back in California, studies have shown how some rain shadow effects can lead to flooding on one side and protection of cities and people on the other, as with the rain shadow caused by the Santa Lucia Mountains protecting the city of Santa Cruz along the central coast range of the state (Ralph et al. 2003).   

  

      

Information:
     Parish, TR.  1982.  Barrier winds along the Sierra Nevada Mountains.  Journal of Applied Meteorology 21:925-930.
     Ralph, FM, PJ Neiman, DE Kingsmill, POG Persson, AB White, ET Strem, ED Andrews, and RC Antweiler.  2003.  The impact of a prominent rain shadow on flooding in California's Santa Cruz Mountains:  A CALJET case study and sensitivity to the ENSO cycle.  Journal of Hydrometeorology 4:1243-1264.  
     Tattersfield, P, CM Warui, MB Seddon, and JW Kringe.  2001.  Land-snail faunas of afromontane forests of Mount Kenya, Kenya: ecology, diversity and distribution patterns.  Journal of Biogeography 28(7):843-861.