CBD First National Report - Saudi Arabia (English version)

4. The Cuesta region (Sedimentary Najd)5. Aeolian Sands: an-Nafud, Ad-Dahna, Al-Jafurah, Ar-Rub’ al-Khali6. As-Summan and Widyan Plateaus7. Arabian Gulf coastal region8. The Red Sea9. The Arabian GulfClimate1. RainfallSaudi Arabia is an area of dry, stable, subsiding air which gives rise to hot, dry and nearcloudless skies with dry days most of the year. Occasionally disturbed tropical monsoonweather may reach the Kingdom, bringing rain to the south of the country in the summer.In winter, remnants of the mid-latitude low pressure system may penetrate the north ofthe country giving rise to most rain in the region.Precipitation due to high altitude and proximity to the Red Sea augments rainfallalong the south-western escarpment. Daytime on-shore sea breezes force the moist airfrom the Red Sea to ascend, giving rise to afternoon showers and thunderstorms. Annualprecipitation in the mountains south of Taif is above 125 mm and may exceed 600 mm.Map 2.4 in Child and Granger (1990) shows the average annual precipitation in theKingdom. It is a guide as in most areas the precipitation is highly variable andunpredictable.2. Temperature and HumidityTemperatures are subject to considerable diurnal and seasonal fluctuations. Winters(December to February) are cool to warm. Summers (June to September) tend to be veryhot with temperatures above 40º C widespread and common and may approach 50º C.Humidity is generally low, except along the coasts where it may be quite high.Average August temperature in Jeddah 32º C but may reach 49º C, winter temperatureaverage 24º C, and relative humidity varies seasonally between 55% and 65%.Summer months in Riyadh are intensely hot with a daily maximum about 45º C. Wintersare cooler, with a maximum temperature of 22º C declining to 10º C or lower. Relativehumidity also varies with seasons with typical summer humidity of between 15 to 20 %.The Gulf coast is warm and humid in summer with average maximum of 42º Cand winter maximum average of 22º C. Humidity varies seasonally greatly from 40% insummer to about 70% in winter.The Arabian GulfThe Arabian Gulf extends from the Straits of Hormuz in the south to the Shatt al-Arab inthe north. It is a narrow sea, about 200 to 300 km wide and 1000 km long. It is mostlyquite shallow with an average depth of 35 m. the deepest water being found closer to theIranian coast (80m) and the Strait of Hormuz (100 m).Twenty thousand years ago, when the world was passing through an ‘ice age’,much of the water now in the sea was locked up in great ice sheets and the sea level wasabout 120 m lower than it is today. The Gulf was dry. The Tigris and Euphrates riversflowed along the coast of Iran and met the sea at the Strait of Hormuz. The sea onlyreached its present level about five thousand years ago. The plant and animal18