Where Are the Desert Biomes Located?

Desert biomes cover roughly one-third of Earth’s land surface and span every continent, but they cluster in predictable geographic bands rather than appearing randomly. The largest concentration sits along the subtropical latitudes, between about 15° and 35° north and south of the equator, where sinking dry air creates the Sahara, the Arabian Desert, and the Australian Outback. Beyond that belt, deserts also form in the rain shadows of major mountain ranges, deep in continental interiors far from any ocean moisture, along cold-current coastlines, and at the poles themselves. The pattern is more varied than most people expect, and the boundaries are shifting.

The Subtropical Desert Belt

The single biggest cluster of desert biomes on Earth sits in two bands that wrap around the globe, one in each hemisphere. In the Northern Hemisphere, these subtropical deserts stretch from the Sahara in North Africa through the Arabian Peninsula and into the Thar Desert of northwestern India. In the Southern Hemisphere, the same atmospheric pattern produces the Kalahari and Namib in southern Africa, a large arid zone across central and western Australia, and parts of the Atacama along the Pacific coast of South America.

The reason these deserts all line up at similar latitudes has to do with how air circulates across the tropics. Warm, moist air rises near the equator, drops its moisture as tropical rainfall, then flows poleward at high altitude before sinking back toward the surface around 20°–35° latitude. As that air descends, it compresses and warms, making it extremely dry. Climate simulations consistently show a weakening and poleward expansion of this large-scale circulation pattern under global warming, which has implications for where these deserts sit in the future.¹

The Sahara alone covers about 9 million square kilometers, making it the largest hot desert on Earth. It dominates much of North Africa from the Atlantic coast to the Red Sea. South of it, the Arabian Desert extends across Saudi Arabia, Yemen, Oman, and into the Persian Gulf states. East of that, the arid belt continues through Iran and into Pakistan’s Thar. In the Southern Hemisphere, Australia’s interior is overwhelmingly arid or semi-arid, with deserts like the Great Victoria, the Gibson, and the Simpson covering much of the continent’s western and central land mass.

Rain Shadow Deserts and the Influence of Mountain Ranges

Not all deserts sit along the subtropical belt. Some of the most dramatic arid landscapes on the planet owe their existence to nearby mountains that intercept moisture before it can reach them. When moist air encounters a tall mountain range, it rises, cools, and drops its water as rain or snow on the windward side. The air that spills over the leeward side is dry, creating what geographers call a rain shadow.

The deserts of Central and East Asia offer the clearest example. Northern China’s desert zone, covering roughly 1.5 million square kilometers, forms the world’s largest mid-latitude continental interior desert, and its existence is tightly linked to the rise of the Tibetan Plateau.² As the plateau rose over millions of years, it progressively blocked moisture-laden air from the Indian Ocean, drying out the interior to its north. The Gobi, Taklamakan, and other Central Asian deserts are all downstream of this effect.

Modeling work has shown that the uplift of the Pamir Mountains played an especially large role in the aridification of inland Asia, reducing annual precipitation across a wide area of northwest China through this rain shadow mechanism.³ Research on atmospheric dynamics has shown that once mountain ranges reach a certain height relative to wind speed, the downstream precipitation can effectively vanish, with cloud mass on the dry side dropping by as much as 90%.⁴

South America provides another striking case. The Andes run the full length of the continent, and on their eastern rain shadow in southern Argentina, Extra-Andean Patagonia sits under arid conditions despite being at a relatively high latitude. The mountains intercept moisture from the Pacific, leaving the lowlands to the east dry enough to support saline lakes and sparse vegetation rather than the forests found at the same latitude in Chile.⁵ In North America, the Great Basin Desert of Nevada and Utah sits in the rain shadow of the Sierra Nevada and Cascade ranges.

Coastal Deserts Along Cold Ocean Currents

Some of the driest places on Earth sit right next to the ocean, which seems paradoxical until you consider the temperature of the water. Where cold ocean currents flow along a continental west coast, they chill the air above them, creating a stable layer that resists the formation of rain clouds. Fog rolls in, but genuine rainfall almost never arrives.

The Atacama Desert of Chile and Peru is the classic example. It hugs the Pacific coast and is one of the driest and possibly oldest deserts in the world, so parched in places that it has been used as an analog for dry conditions on Mars.⁶ Some weather stations in the Atacama’s core have recorded years with zero measurable rainfall. Along the coast, fog is often the primary source of moisture for any life that persists. Cacti in the coastal zone rely on isotopically enriched fog water, while those at higher Andean elevations depend more on rainfall and snowmelt, a gradient that tracks closely with distance from the coast and altitude.⁷

The Namib Desert of southwestern Africa operates on a similar principle. The cold Benguela Current runs along the coast of Namibia and Angola, stabilizing the air and suppressing rainfall. Namibia’s vegetation reflects an aridity gradient that runs from north to south, shifting from open woodland in the wetter northeast to low open shrubland in the drier south, with annual rainfall ranging from about 600 mm down to 100 mm.⁸ The Namib itself, in the most coastal and southern portions, receives far less than that minimum. Other coastal deserts formed by cold currents include parts of Baja California along Mexico’s Pacific coast.

Polar Deserts

When most people hear “desert,” they picture sand dunes and scorching heat, but the largest desert on Earth is covered in ice. Antarctica qualifies as a desert because its interior receives very little precipitation, often less than 50 mm of water equivalent per year. The extreme cold means the air can hold almost no moisture, and what little snow does fall rarely melts, accumulating over millennia into ice sheets rather than cycling through the landscape the way water does in wetter biomes.

The Arctic, too, contains extensive polar desert, particularly across the northern reaches of Canada’s Queen Elizabeth Islands, northern Greenland’s ice-free margins, and parts of Svalbard. These landscapes receive scant precipitation and support only sparse, low-lying vegetation like mosses and lichens during the brief summer. The defining feature of a polar desert is not temperature but aridity: the air is simply too cold and stable to deliver meaningful moisture.

Including both polar regions, deserts occupy a far larger share of the planet’s surface than many people realize. The Antarctic ice sheet alone covers about 14 million square kilometers, which makes it larger than the Sahara.

Continental Interior Deserts Far From Any Coast

Even without mountains to block moisture, sheer distance from the ocean can dry a landscape into desert. Air masses lose moisture progressively as they travel overland, so regions deep within large continents tend to be arid simply because all the rain has already fallen before the air arrives. Central Asia’s Karakum and Kyzylkum deserts in Turkmenistan and Uzbekistan are partly rain-shadow deserts and partly distance deserts, sitting thousands of kilometers from the nearest significant moisture source.

Northern China’s desert zone illustrates how these factors combine. The deserts there are continental in the sense that they occupy the deep interior of the Eurasian landmass, but their aridity was dramatically intensified as the Tibetan Plateau rose and cut off the Indian monsoon moisture that might otherwise have reached them.² The expansion of these deserts over the past 3.5 million years tracks the stepwise uplift of the plateau, providing a geological record of how the location of a desert biome can be “created” by tectonic changes that rearrange moisture pathways.

How Desert Hydrology Works Without Rivers to the Sea

A distinctive feature of many desert locations is that their water never reaches the ocean. Hydrologists describe these as endorheic basins, which are internally drained areas where water flows inward to a terminal lake, wetland, or salt flat and then evaporates. A large fraction of drainage in arid and semi-arid landscapes is classified this way.⁹

The Salar de Atacama in Chile is one of the world’s most studied examples. Water that infiltrates from the surrounding mountains rises through a mixing zone where fresh water meets dense brine, and the salt flat’s core acts as an almost hydraulically isolated area.¹⁰ These endorheic systems define the visual character of many deserts: playas, salt pans, and ephemeral lakes that appear after rare storms and vanish in weeks. The Bonneville Salt Flats in Utah, the Etosha Pan in Namibia, and the vast salt flats of Iran’s Dasht-e Kavir are all products of this process.

However, increasing evidence suggests that not all of these basins are truly closed. Subsurface groundwater exchanges can connect basins that appear isolated on the surface, with real consequences for water availability and ecosystem survival.⁹ This matters enormously for desert communities that depend on groundwater: the water budget may not be as simple as “what falls here, stays here.”

Desert Boundaries Are Not Fixed Lines

On a map, deserts look like neatly bounded regions, but in reality, the edges blur into transition zones that can stretch for hundreds of kilometers. The Sahel, the band of semi-arid land running across Africa between the Sahara and the wetter savannas to the south, is the most studied of these boundaries. Research using satellite vegetation data and machine-learning classification has mapped this desert-to-grassland transition zone and found that it is expanding both northward and southward, a trend projected to continue over the coming decades.¹¹

At a much finer scale, the boundary between a desert and an oasis can be surprisingly sharp. Studies in China’s Taklimakan region have measured the transition between productive oasis vegetation and barren sand desert, finding that vegetation indices and temperature conditions intersect within just 30 to 90 meters of the oasis boundary, depending on the measurement scale used.¹² Beyond about 200–300 meters, the two measurement curves run roughly parallel, meaning the transition is essentially complete. These micro-transitions matter for agriculture, irrigation planning, and efforts to combat desertification at the local level.

Climate Change and Shifting Desert Margins

The location of desert biomes is not permanently fixed, and climate change is actively redrawing the map. The subtropical dry zone that drives the Sahara, Arabian, and Australian deserts appears to be creeping poleward. Observational studies have documented a poleward expansion of the tropical belt and subtropical dry zone by around two to three degrees of latitude over recent decades.¹³ Climate model projections show this trend continuing under warming scenarios, with the large-scale atmospheric circulation that creates subtropical deserts weakening and shifting farther from the equator.¹

The drying effect is not perfectly uniform around the globe, though. Research has found that while you would expect the expansion to bring drying to all regions on the poleward margins of the subtropics, the actual pattern is patchy and depends on regional factors like ocean temperatures and land topography.¹⁴ Southern Europe, the Mediterranean, southwestern Australia, and parts of southern Africa are among the regions most vulnerable to this subtropical drying. In these areas, landscapes that are currently semi-arid could functionally become desert within the lifetimes of people alive today.

An older but influential assessment cautioned that when evaluating desert expansion, human land use often matters more than climate shifts. The impact of overgrazing, unsustainable agriculture, and deforestation on dryland degradation can dwarf the effect of modest changes in rainfall, at least on the timescales of a few decades.¹⁵ Desertification, in other words, is often as much a story about land management as about shifting climate zones.

When the Sahara Was Green

The Sahara’s current location as the world’s largest hot desert is a geologically recent development. Paleoclimate records have documented at least two “Green Sahara” periods during which the region received enough rainfall to support lakes, rivers, and savanna vegetation. One occurred during a warm interval roughly 84,000 to 77,000 years ago, and another during the early to mid-Holocene, from about 9,000 to 4,000 years ago.¹⁶ Cave records from northwest Africa confirm these same two wet intervals, with increased precipitation synchronous in both cases.¹⁷

The Green Sahara episodes were driven by shifts in Earth’s orbital geometry that strengthened the African monsoon, pushing tropical rainfall hundreds of kilometers north of its present limit. Rock art in what is now hyper-arid southern Libya depicts hippos, crocodiles, and cattle herding, all dating from the last green phase. The implication is that the location of a desert biome can change dramatically on timescales of thousands of years, even without human intervention. The Sahara as we know it is a snapshot, not a permanent feature.

Biological Soil Crusts and the Living Desert Surface

One reason desert locations matter ecologically is that desert soils are not simply inert sand. Across most desert surfaces worldwide, a living layer of cyanobacteria, algae, lichens, and mosses forms what researchers call biological soil crusts. These crusts bind soil particles together with filamentous sheaths, making the surface far more resistant to wind and water erosion than bare sand would be.¹⁸

Wind tunnel experiments have shown that undisturbed biological soil crusts in arid lands can resist wind forces well above anything those sites normally experience, meaning the surface is effectively stable against erosion as long as the crust remains intact.¹⁹ Disturbance is the problem. Off-road vehicles, livestock trampling, and construction can destroy crusts that took decades to form, triggering dust storms and accelerating desertification. In desert locations around the world, from the Colorado Plateau to the Negev to the Australian interior, the health of these crusts is a quiet indicator of whether a desert ecosystem is stable or degrading.

Desert Cities and the Challenge of Water

More people live in deserts than at any point in history. Many arid-region cities sit in highly urbanized countries: the United States, Israel, Australia, Saudi Arabia, the United Arab Emirates, and Qatar all have urban populations exceeding 80% of their total population. Projections suggest that runoff in many of these regions could decrease by 10 to 40% by mid-century across southern Africa, southern Europe, the Middle East, and mid-latitude western North America.

Cities like Phoenix, Riyadh, Dubai, and Lima have grown explosively despite sitting in or adjacent to desert biomes, relying on a mix of deep aquifer extraction, desalination, long-distance water transfers, and aggressive conservation programs. The geographic reality that these cities occupy desert locations is not incidental to their futures; it is the defining constraint. As the subtropical dry zones expand poleward and rain shadow deserts intensify with continued tectonic and climatic shifts, the map of where desert biomes sit will keep changing, and the infrastructure built in and around them will have to change with it.