Origin and location

A common location of deserts is the western littoral of continents in the vicinity of the subtropical high. Coastal deserts are particularly well developed along the subtropical west coasts of South America and Africa, less so in the United States and Australia (Fig. 20.1). The desert along the Somali Coast of eastern Africa and the Danakil Desert to the north of it exhibit some of the same characteristics but these deserts are not linked to any of the subtropical high-pressure cells. The major coastal deserts, also called fog deserts, have similar causes of aridity. They also have certain characteristics that distinguish them from other desert regions. These include not only the high frequency of fogs, but also moderate temperatures, limited annual temperature range, moderate diurnal range, and high relative humidity, compared with inland deserts.

The fogs are an important part of the coastal ecosystem in these deserts (Gutiérrez et al. 2008) and vegetation patterns are very sensitive to their distribution. Dense fog “oases” are common in various niches in the hyper-arid Peruvian-Atacama Desert (Cereceda et al. 2008a), but they are found in many other deserts. In many locations, the fog actually sustains forests. Examples are the cloud forests in eastern Mexico (Vogelmann 1973), relict forests in Oman (Hildebrant and Eltahir 2006), and forest niches in north central Chile (del-Val et al. 2006). In some cases, fog is the dominant or sole moisture source. The fogs provide not only moisture, but also shading, facilitating vegetation survival through periods of drought (Fischer et al. 2009). The shading, a result of the low clouds producing the fog, may be more important than the accompanying moisture (Williams et al. 2008).