Badain Jaran, a desert landscape in the far west of Inner Mongolia, belongs to the greater Gobi system and lies on the Alxa Plateau at an altitude of about 1200 m. Geographically, it encompasses the fringe parts of three Chinese provinces – Inner Mongolia, Gansu, and Ningxia – and in scientific and popular literature, it is described as a “land of dunes and lakes” due to the unusual coexistence of megadunes and hundreds of interdunal water mirrors. This part of the Gobi landscape is also recognized on a global level: the area has been inscribed on the UNESCO World Heritage List, further highlighting its geological, hydrological, and biological distinctiveness.

An image captured by the radar instrument of the Copernicus Sentinel-1 mission in September 2025 provides an exceptionally clear display of the rhythm of sand and water. In the radargram, series of parallel sand ridges are drawn as dense, regular grids, while lakes stand out as dark planes sunken among the dunes. Since this involves synthetic aperture radar (SAR) imaging, the contrast between smooth water surfaces and rough sandy morphologies is emphasized regardless of the time of day and meteorological conditions, making Sentinel-1 an ideal tool for long-term observation of such a dynamic environment.

China's third-largest desert and geographical framework

Badain Jaran occupies approximately 49,000 square kilometers, ranking it among the largest deserts in East Asia and the third largest in China. It is located in the center of the Alxa Plateau – a vast highland on the southern edge of the Gobi – between the Helan Mountains and the Yellow River to the east and the Qilian and Yabulai Mountains areas to the south and southwest. Such a spatial position implies a continental climate with strong thermal amplitudes, rare precipitation, and numerous winds that model the surface almost throughout the year. Between wide fields of dunes, straits and beds of intermittent streams appear, which briefly come to life during the storm season and transport finer material into interdunal hollows.

The relief is “simple” at first glance – a sea of sand – but exceptionally diverse in detail. The lower parts of closed interdunal basins are filled with water that varies in level and salinity in an annual cycle, while peripheral oases and isolated rock outcrops (inselbergs) testify to older, lithologically more resistant phases of landscape development. In aerial and satellite imagery, a pallet of blue and black lake dots emerges from the almost monotonous bright sand, giving the desert a recognizable “spotted” texture.

Megadunes: “towers” of sand up to 460 meters high

Badain Jaran is known for densely packed rows of megadunes – static, stabilized dunes of impressive dimensions. At numerous locations, the relative height exceeds 200 meters, and the highest measured reaches about 460 meters, meaning this desert system gathers the highest stabilized sand dunes in the world. The dunes are most often crescent-shaped to complex forms, with multiple ridges and secondary crests, and their formation and maintenance are linked to a long-term wind regime and the presence of solid cores in the substrate that “anchor” vast volumes of sand.

The most famous peak of the dune “relief vocabulary” is Bilutu – a massive dune whose peak rises to approximately 1600 m above sea level, while the relative height compared to the surrounding terrain is measured in hundreds of meters. Although “ordinary” sand waves in deserts usually move, such megadunes in Badain Jaran are largely stationary: their shapes change slowly, and volumes remain stable thanks to a combination of winds, moisture that capillarily binds lower layers, and lithological frameworks. In winter months, peak slopes are often covered by snow, and this seasonal “blanket” further reduces the mobility of surface sand.

Lakes among dunes: groundwater, springs, and chemical diversity

Scattered among the sandy ridges are more than a hundred lakes – from shallow, extremely saline ones, to deeper and almost entirely freshwater ones. It is precisely these “hidden mirrors” that gave the desert its name: the Mongolian name Badain Jaran translates as “mysterious lakes”. The origin and renewal of their water remain a subject of active research. Numerous hydrogeological and paleolimnological studies point to underground circulation and inflows from regional aquifers fed by infiltration from nearby mountains – primarily from the Qilian massif – and from contact zones of rock and sand at the edges of the plateau.

These lakes function as a natural “index” of climate change in the desert. In drier periods, the level drops, edges recede and reveal dusty salt flats; in moisture-richer seasons, the surface expands, and the color shifts from dark green to blue hues. Sediment cores from the bottom of individual lakes – such as Sayinwusu – preserve records of changes in productivity and salinity over the last hundred years or more, linked to regional climate oscillations and changes in the wind and precipitation regime. Chemical composition varies from fresh, oligotrophic waters to salt-saturated lakes, in which crystals of the marginal ring remain as a witness to intense evaporation.

“Singing” sands: dune acoustics as a phenomenon

Badain Jaran is one of the rare places in the world where the phenomenon of “singing dunes” can be experienced. On warm, dry summer days, when slopes are steep, and grains are homogeneous and well-rounded, upon the movement of the upper layer – whether by wind or sliding down the slope – a collective sliding and rubbing of grains occurs, producing a deep hum or a high pitch. The frequency and duration of the sound depend on the size and composition of grains, moisture, and slope, and the phenomenon itself can last from a few seconds to several minutes. The acoustic “concert hall” of dunes depends on a precise combination of factors: “singing” is most pronounced when grains are quartz and relatively equal in size, when moisture is low, and when the slope is on the verge of stability.

Living world in the “sea of sand”

Despite the association with “empty” space, Badain Jaran is an ecosystem of high diversity. On lake edges and in interdunal hollows, plants adapted to extremes develop – from salt-tolerant halophytes to deep-rooted shrubs that stabilize the sand. Nightlife takes on a key role: many animals are active only after sunset when temperatures drop and humidity rises. The UNESCO assessment highlights that the area, despite sandy dominance, abounds in plant communities and provides habitats for numerous nocturnal animals, and water surfaces serve as resting and feeding grounds for migratory birds and as a permanent oasis for reptiles, amphibians, and invertebrates.

The vegetation patch that holds the dunes together is not only aesthetic but also functional: grasses and shrubs trap snow and dew, their roots bind the surface layer and reduce erosion, and shade and microrelief lower soil temperature. This creates conditions for “oases” which, although small, initiate a chain of life in which water, plants, insects, and birds form a stable microcosm amidst the harsh desert.

Climate, seasonality, and winter snow

The climate of Badain Jaran is distinctly continental: summers are hot and dry, winters cold, with occasional snow. The snow cover which, especially on the higher crests of megadunes, remains for several days or weeks, acts as temporary “cement” on surface layers, reducing sand mobility in the cold season. In clear satellite images, winter stripes of snow emphasize the geometry of crests and reveal how much the dunes, although exposed to wind, are stable in their foundation. In the summer season, conversely, the surface overheats quickly; then “avalanches” of fine sand occur more frequently on slopes, triggering sound phenomena, and lakes evaporate more intensely.

Image from space: why radar is key

For observing such a landscape, the advantage of a radar sensor is decisive. Unlike optical cameras that depend on daylight and are often “blinded” by sandstorms or clouds, C-band SAR on Sentinel-1 satellites records structural differences in roughness and dielectric properties of the surface, so sand, rock, and water are clearly separable. This enables mapping the position and width of dunes, detecting changes in lake shorelines from season to season, tracking surface moisture after rare monsoon episodes, and precise comparison of the landscape through time thanks to uniform imaging geometry.

In September 2025, the radar image of the area reveals dense “packets” of parallel ridges, indicating a high density of megadunes in the center of the desert, while dark “eyes” of lakes are mostly located in valleys between three or more dunes. In the backscatter spectrum, water is almost black (specular reflection sends energy away from the sensor), dunes are bright to medium-toned (scattering on rough slopes and edges), and rocky oases or protrusions are even brighter. Such a visual “negative” allows even a layman to understand the logic of the landscape and the spatial relationship of water and sand.

Culture and traces of man

Amidst the desert, on the shore of one of the lakes, is also the Buddhist Badain Jaran Temple from the late 19th century – an architectural and historical rarity that has been preserved due to isolation through the turbulent periods of the 20th century. The oasis around the temple testifies to the skill of adaptation: water supply relies on springs and shallow wells, and the movement of sand masses is limited by vegetation and low dry stone walls. Traces of nomadic animal husbandry and paths connecting fringe towns with the desert interior are today read even on high-resolution satellite images – tiny wheel tracks and thin dust remain on leeward sides, while on the windward side, they are often erased by the very first major storm.

Tourism, access, and preservation

Access to Badain Jaran is possible via routes from Alxa League and the city of Ejin, and the most attractive points – such as the ascent to Bilutu or crossing over fields of lakes – are often visited by special off-road vehicles with local guides. The increase in visitation in recent years has also brought new management rules: UNESCO status draws attention to the necessity of traffic control, protection of sensitive lake shores, and visitor education about the fragility of sandy ecosystems. Limiting driving outside marked routes, banning littering, and carefully planned infrastructure (viewpoints, rest areas, educational trails) are key to preserving natural processes that create and maintain this landscape.

Given the sensitivity of lake systems to disturbances in water balance, local authorities and scientists emphasize the importance of constant monitoring of water level and chemistry, as well as checking the state of vegetation on the edges. In this regard, an integrated approach combining satellite observations (SAR and optics), field measurements, and traditional knowledge of nomadic communities provides the most reliable picture of status and trends.

Wind as a sculptor: processes that build and destroy

Dominant winds in Badain Jaran – which change throughout the year – shape asymmetric dune profiles: the windward side is most often gently sloped while the leeward side is steeper and prone to sand slides. In the warmer part of the year, the surface dries easily, and grains become more mobile; in the colder and wetter period, cohesion increases, so activity temporarily decreases. Occasional sandstorms surge in waves, but precisely the large volume and cores of megadunes cause the overall macro-shape to remain stable for a long time, while details – ridges, furrows, and tiny waves – are constantly redrawn.

Scientific challenges: from the origin of lakes to the future of sand

Although research has intensified, the origin and sustainability of the lakes have not been fully clarified. Hydrogeological models suggest that groundwater inflows come from multiple directions – including transfer from deep regional aquifers and seepage from contact zones of rock and sand – and the contribution of modern precipitation depends on the unpredictable synthesis of monsoons and local storms. Analyses of sediment cores indicate phases of higher and lower salinity, which can be linked to broader climate oscillations. In the future, a combination of field methods (piezometers, isotopes, geochemistry) and advanced satellite sensors (multiple polarizations, higher spatial and temporal resolution) will help in quantifying the balance between losses by evaporation and inflow from aquifers.

Badain Jaran in the public eye

Although for centuries outside main trade and cultural flows, Badain Jaran has been gradually affirming itself in the public eye over the last decade. Photographs and recordings highlighting contrasts – blue lakes wedged between creamy crests, traces of snow on sand waves, the soundscape of “singing” slopes – increasingly circulate in global media and social networks. This brings a double message: on one hand, it reveals to everyone the beauty of one of the most unusual desert landscapes on Earth, and on the other, it warns that this is a sensitive system in which human presence must be measured.

Copernicus radar images allow this balance to be monitored without interruption. They are the base of many scientific papers on hydrological dynamics of lakes and the “breathing” of dunes, but also a practical tool for local authorities for route planning, checking traffic impact, and even for early storm warning. Comparisons of scenes from different years – for example between the dry 2010s and wetter episodes in the mid-2020s – show how water surfaces expand and shrink in a rhythm linked to regional rainfall and groundwater inflows.

As a window into geologically fast, yet to the human eye still subtle dynamics, Badain Jaran represents an ideal laboratory where geomorphology, climatology, hydrogeology, and acoustics merge. Whether we observe it from the air, from a dune peak in the early morning, or listening to sand “singing” underfoot, it is a landscape that constantly changes its face – and in doing so persistently keeps its secrets.