of sheep and other livestock A range of deserts: the Nefud in the north, which is stony; the Rub' al Khali or Great Arabian Desert in the south, with sand estimated to extend below the surface; between them, the Dahna Mountains Stretches of dry or marshy coastland with coral reefs on the Red Sea side (Tihamah) Oases and marshy coast-land in Eastern Arabia, the most important of which are those of Al Ain (Tawam in the United Arab Emirates and Oman) and Al-Hasa (in Saudi Arabia), according to one author Tropical monsoon coastline in Dhofar and Al-Mahra (known as Khareef in the Arabian Peninsula). Arabia has few lakes or permanent rivers. Most areas are drained by ephemeral watercourses called wadis, which are dry except during the rainy season. Plentiful ancient aquifers exist beneath much of the peninsula, however, and where this water surfaces, oases form (e.g. Al-Hasa and Qatif, two of the world's largest oases) and permit agriculture, especially palm trees, which allowed the peninsula to produce more dates than any other region in the world. In general, the climate is extremely hot and arid, although there are exceptions. Higher elevations are made temperate by their altitude, and the Arabian Sea coastline can receive surprisingly cool, humid breezes in summer due to cold upwelling offshore. The peninsula has no thick forests. Desert-adapted wildlife is present throughout the region. According to NASA's Gravity Recovery and Climate Experiment (GRACE) satellite data (2003–2013) analysed in a University of California, Irvine (UCI)-led study published in Water Resources Research on 16 June 2015, the most over-stressed aquifer system in the world is the Arabian Aquifer System, upon which more than 60 million people depend for water. Twenty-one of the thirty seven largest aquifers "have exceeded sustainability tipping points and are being depleted" and thirteen of them are "considered significantly distressed". A plateau more than high extends across much of the Arabian Peninsula. The plateau slopes eastwards from the massive, rifted escarpment along the coast of the Red Sea, to the shallow waters of the Persian Gulf. The interior is characterised by cuestas and valleys, drained by a system of wadis. A crescent of sand and gravel deserts lies to the east. Mountains There are mountains at the eastern, southern and northwestern borders of the peninsula. Broadly, the ranges can be grouped as follows: Northeast: The Hajar range, shared by the UAE and northern Oman Southeast: