The Kingdom of Saudi Arabia is the largest state on the Arabian Peninsula, with extensive coastlines on both the Red Sea and the Arabian Gulf and common borders with all other Arabian countries and Jordan and Iraq in the north. Topographically, the country is very varied, with extensive mountain ranges reaching 3,000 m and limestone escarpments, vast sand deserts, lava deserts and coastal and inland sand/gravel plains.
However, the basic physiographic units are well defined and, in a southwest to northeast transect across the country, the major units are the Red Sea coastal plain or Tihamah, the mountains of the Red Sea rift valley (Hejaz in the north, Asir in the south), the western plateau and northern plains including several major lava desert areas (harrats), the central and eastern sand deserts (Nafud in the north and Rub 'al Khali in the south and east) linked by other dune systems, and finally the eastern, Gulf, coastal plain (see Newton & Symens, 1994, for more details). The climate is essentially arid to hyper-arid, although the southwestern mountain ranges receive higher than average (<50 mm) rainfall (300500 mm) and, when combined with the often persistent low cloud, effective precipitation is high enough to support evergreen juniper forest. These high orographic rainfalls are primarily supported by the Northwest Indian Ocean summer monsoon (Siraj, 1984; Tinley, 1994). As the Kingdom spans 16°-32°N and altitude ranges from sea level to 3,000 m, temperature and humidity vary greatly. Subzero nights are frequent in the north and daily summer temperatures are often in the range 35°-45°C. Humidity is highest in the summer, especially on the Gulf and southern Red Sea coastlands.
Biogeographically, the Kingdom has a unique setting. The Saharo-Sindian desert belt spans the country, with a distinctive faunal and floral assembly of its own, but this is overlain with significant Western Palearctic elements in the north, some Indo-Malaysian influence in the east and a near total Afrotropical fauna and flora present in the southwest. The latter area exhibits the highest degree of faunal endemism on the Arabian Peninsula (ICBP, 1992).
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Kingdom of Saudi Arabia
