Rub’ al Khali Desert

Category: Desert Biomes.

Geographic Location: Middle East.

Summary: Known as the Empty Quarter, this desert nevertheless supports an array of drought-tolerant plants and some opportunistic fauna.

The Rub’ al Khali Desert is the southernmost of the Arabian Peninsula major deserts, and is the largest sand desert on Earth. Located primarily in southeastern Saudi Arabia, and also spreading to parts of Yemen, Oman, and the United Arab Emirates (UAE), this desert is often called the Empty Quarter. The Rub’ al Khali Desert is relatively uninhabited and infrequently explored, although some nomadic Bedouins, such as the Al-Murrah, range its perimeter.

Rub’ al Khali comprises roughly 200,000 square miles (520,000 square kilometers); it is 620 miles (1,000 kilometers) across, east to west; and 310 miles (500 kilometers) wide, north to south. Surface elevation varies from 2,625 feet (800 meters) in the southwest to sea level not far from the Persian Gulf in the northeast. Feldspar in the mineral base produces a reddish-orange tint to the sand dunes rising to 820 feet (250 meters). Gravel and gypsum stretches cover much of its area.

Across the core of the desert are features of hardened calcium carbonate, gypsum, marl, and clay; these are thought to have been shallow lakes 5,000–37,000 years ago. Along with opal deposits, the calcium carbonate in particular indicates bygone plants and algae. Bits of flint and petrified wood found in quartzite mounds also speak to bygone vegetation and wetlands that likely hosted reeds, cattails, and salt cedar trees.

The Rub’ al Khali evidences extreme temperature swings, with summer temperatures in some places shifting from below 32 degrees F (0 degrees C) at night to over 140 degrees F (60 degrees C) at noon. On average, the daily maximum temperature is 117 degrees F (47 degrees C) in July and August, and the daily minimum is 54 degrees F (12 degrees C) in January and February. The biome has very low humidity with scarcely any precipitation; in winter, exceedingly light rains may fall in the northern area, or mists may blow in off the Arabian Sea, stimulating vegetation for the following years. Annual rainfall of less than 1.4 inches (35 millimeters) indicates a hyperarid climate; there is no regular seasonal precipitation.

Shamal winds, generally from the northwest, shape the dunes and keep them shifting. The shamal also kicks up sandstorms. The southern monsoon is felt here in February and March, not as a rainfall event, but as strong persistent winds from the south.

Flora

The sea of shifting sand dunes, extremely high temperatures, and scant rainfall produce one of the driest places on Earth—only very hardy plants are supported here. Floral biodiversity is limited, with some sources reporting a total of 37 species of flora: 20 in the sandy desert and 17 on its edges. The ground-hugging woody shrub Calligonum crinitum is found on dune slopes. In the pans between dunes and scattered drainage channels are scrub flora such as Dipterygium glaucum, Limeum arabicum, and the fine-leafed succulent Zygophyllum mandavillei; sedge (Cyperus conglomeratus); and the trees Acacia ehrenbergiana and ghaf (Prosopis cineraria).

Other flora include the fire bush, or abal (Calligonum comosum), found generally in the UAE portions of the desert; and annual herbs such as Danthonia forskohlii. Oman’s part of the desert has the Wahiba sands, with ghaf woodlands that extend approximately 50 miles (85 kilometers) in length by 12 miles (20 kilometers) wide. Other widely established flora in the Rub’ al Khali Desert biome include saltbush (Cornulaca arabica), flowering parasitic plants called dhanun, and desert candle (Caulanthus inflatus).

Fauna

Fauna found more generally around the fringe scrubland and scattered stands of woodland include birds such as warblers, pied wheatears, ravens, falcons, and long-legged buzzards. The greater flamingo (Phoenicopterus ruber) took up breeding grounds at the Persian Gulf verge of the desert in the 1990s, following a 70-year hiatus. Houbara bustards (Chlamydotis undulata) have also been sighted.

Among mammals, the sand and mountain gazelle (Gazelle subgutturosa) and white or Arabian oryx (Oryx leucoryx) are protected in the Uruq Bani Ma’arid preserve on the western edge of the desert. The Nubian ibex (Capra nubiana) and Arabian oryx (Oryx leucoryx) are two endangered species that find some refuge here. Regardless of such human mandates, the Arabian wolf (Canis lupus arabs), striped hyaena (Hyaena hyaena), sand cat (Felis margarita), and Ruppell’s fox (Vulpes rueppellii) prowl for such ungulates, as well as for smaller prey such as the brown hare (Lepus capensis).

The Rub’ al Khali clearly had a more forgiving climate in prehistoric times. Fossilized bones of oryx, gazelle, camels, wild asses, and other large mammals have been found in the petrified lake mud, pointing to robust spreads of vegetation capable of supporting herds of herbivores. Some shellfish fossils are also reported. There is even fossil evidence of hippopotamus and water buffalo.

Tribes and Outsiders

Bedouin tribes such as the Al-Murrah and Al-Dawasir typically range the northern side of the Rub’ al Khali Desert. To the east are seen their nomadic brethren the Al-Manasir and Al-Duru; while to the south and west are the Al-Kathir, Al-Rawashid, Al-Manahil, and Sa’ar tribes. These peoples have adapted and evolved their traditional ways of living in pastoral balance within this biome since time immemorial. Subsistence comes to them in the form of herding, small-scale farming, and hunting.

At the other end of the human activity scale are modern industrial enterprises from around the world that come here to explore, develop, and exploit such hidden riches of the Rub’ al Khali region as oil, natural gas, sulfur, and phosphates. Shaybah, Saudi Arabia, near the eastern edge of the desert, has been a crude oil production site for more than 50 years. Infrastructure construction and pollution are threats to the environment of the Rub’ al Khali, as are wildlife poaching, off-road driving, larger-scale agriculture—and even the incidence of camel and goat overgrazing by the nomadic herds.

The desert is vulnerable to climate change. A slight temperature increase from global warming will increase evaporation, reducing surface moisture. Experts predict that by the end of the century, the temperature may increase by 39 to 41 degrees Fahrenheit ( 4 to 5 degrees Celsius), which would likely kill off any plant life in the desert.

Bibliography

Almutlaq, Fahad, et.al. "Calculation of the Rub' al-Khali Sand Dune Volume for Estimating Potential Sand Sources." Remote Sensing, 2 Mar. 2022, doi.org/10.3390/rs14051216. Accessed 1 Sept. 2022.

Clark, Arthur. “Lakes of the Rub’ al-Khali.” Saudi Aramco World 40, no. 3 (1989).

Dunham, K. M. “Population Growth of Mountain Gazelles (Gazella Gazella) Reintroduced to Central Arabia.” Biological Conservation 81 (1997).

"The Fearful Beauty of Rub' al-Khali." 100 Most Beautiful Sites in the World, www.100-beautiful-sites-in-the-world.com/rub-al-khali.html. Accessed 1 Sept. 2022.

Thesiger, Wilfred. Arabian Sands. London: Penguin Books, 1959.