The country occupies 80% of the Arabian Peninsula. A large proportion of the frontiers with United Arab Emirates, Oman and Yemen is not clearly defined, so the exact size of the country is unknown. It is estimated at 1,969,000 km2, so is the tenth largest country in the world, covering 1.64% of the world’s land surface area and being 8% the surface area of Asia.
The climate is hot and dry. Half of the country is uninhabited. In most of Saudi Arabia, vegetation is scarce, with xerophytic plants and shrubs.
The south-western region has mountains reaching altitudes of 3,000 metres and is the greenest and coolest part of the country. The capital, Riyadh, has an average temperature of 42°C in July and 14°C in January, whereas Jeddah, on the west coast, has an average temperature of 31ºC in July and 23ºC in January.
The dominant biome in Saudi Arabia is desert. According to WWF, the country can be divided into six eco-regions:
- Persian Gulf desert and semi-desert on the east coast
- Arabian peninsula coastal desert along the southern half of the west coast
- South-west Arabian foothill savanna
- South-west Arabian high mountains
- Red Sea tropical desert and semi-desert along the north half of the west coast
- Desert and xerophylic mountains of Arabia and Sinai