Geography : The Kingdom of Saudi Arabia is about 1,969,000 km2 occupying four-fifths of the Arabian Peninsula. It is the tenth largest country covering 1.64% of the land area of the world, and 8% of the land area of Asia.

The Kingdom extends from 32º 12' N latitude on the Jordanian border in the north to 16º 00' N at the Yemeni border in the south. It is bounded by the Red Sea in the west and the Arabian Gulf in the east.

Western Saudi Arabia is dominated by a mountain chain running the entire length of the country, known as the Hijjaz and Asir mountains. It runs parallel to the Red sea and rises to between 1300 - 3000 m. above the Tihamah coastal plain to its west. The flat coastal plain along the edge of the Red sea is hot and humid with temperature reaching 45º C in the shade during the summer months, with 90% relative humidity. The winter is considerably cooler but due to the relative warmth of the sea, it is never cold. From this fertile crest it falls towards the east as a desert plateau to the dry interior or the Najd containing the Dahna and Nafud which extends to the great sand desert of the Rub Al Khali (The Empty Quarter). From the Dahna dunes to the east coast the terrain alternate between rocky outcrops and gravel plains. The eastern region lies on the Arabian Gulf coast and contains salt flats (sabkhahs). There are many artesian wells along the coast which are used to irrigate large areas under cultivation around Hofuf and Qatif.

Saudi Arabia divides naturally into seven terrestrial physiographic regions (with 30 sub-regions) and two marine regions (Child and Grainger 1990)

Saudi Arabia is an area of dry, stable, subsiding air which gives rise to hot, dry and near cloudless skies with dry days most of the year. Occasionally disturbed tropical monsoon weather 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 of the country giving rise to most rain in the region.
Precipitation due to high altitude and proximity to the Red Sea augments rainfall along the south-western escarpment. Daytime on-shore sea breezes force the moist air from the Red Sea to ascend, giving rise to afternoon showers and thunderstorms. Annual precipitation in the mountains south of Taif is above 125 mm and may exceed 600 mm.

Temperatures are subject to considerable diurnal and seasonal fluctuations. Winters (December to February) are cool to warm. Summers (June to September) tend to be very hot 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 temperature average 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. Winters are cooler, with a maximum temperature of 22º C declining to 10º C or lower. Relative humidity 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 C and winter maximum average of 22º C. Humidity varies seasonally greatly from 40% in summer to about 70% in winter.