Boundaries

The ecoregion includes the internal basins of the Arabian Peninsula. It is bounded to the east by the Oman Mountains ecoregion [443], the Arabian (= Persian) Gulf, and Lower Tigris & Euphrates ecoregion [441]; to the north by the Upper Tigris-Euphrates ecoregion [443]; to the northwest by a small section of Coastal Levant [436], Orontes [447], and  Jordan River [438] ecoregions; and to the west and south by the Southwest Arabian Coast ecoregion [439].

Topography

A large portion of the ecoregion is a plateau called the Najd, which slopes from the Red Sea escarpment at over 2850 m in the west to 750 meters in the east. There are mountain ranges in the southwest, but mostly isolated wadis draining to deserts. The Jabal Tuwayq is an escarpment with limestone cliffs, plateaus, and canyons that rises in the middle of the Najd.

Freshwater habitats

There are few freshwater habitats over most of this basin. Streams occur near Damascus and Azraq in the north and along the inner slope of the Asir Mountains in the southwest. However, those near population centers, such as Damascus, are heavily polluted. Many streams are intermittent and subject to flash floods. Brackish salt flats exist in some areas, the most famous being the quick sands of Umm al Samim. The Azraq Oasis in Jordan is heavily affected by groundwater extraction for irrigation and water diversion to Amman. The oasis occupies about five km² of permanent pools fed by springs at 600 m altitude.

Terrestrial habitats

The ecoregion spans the Syrian, An Nafud, Ad Dahna, and Rub’ al Khali deserts, which vary from rock and gravel steppe to sand desert. With dunes up to 200 m, the Rub’al Khali (or Empty Quarter) is the largest sand sea in the world. There is limited irrigated land in this ecoregion.

Description of endemic fishes

There are no endemic genera, but four endemic species in two families. These include Aphanius sirhani, Cyprinion mhalensis, Garra buettikeri, and Pseudophoxinus syriacus. Aphanius sirhani is restricted to the Azraq Oasis and attempts are being made to conserve it.

Justification for delineation

The ecoregion has a relatively high level of endemism and affinities with Africa. The Azraq Oasis is a Ramsar site.

Level of taxonomic exploration

Good