The first worldwide oasis map lays out an uncertain future, human expansion, and the exhaustion of sources

Desert agriculture has increased in certain areas despite advancing drought in arid lands

Los oasis de palmeras y desierto cálido, como este de Tamnougalt (Marruecos)
African palm-covered zones like this one in Tamnougalt, Morocco, represent only 4% of the world’s oases. The majority don’t have palm trees, feature lower temperatures, and are located in central Asia.Sergey Pesterev
Miguel Ángel Criado

They represent a mere 1.35% of the planet’s surface, but some of human civilization’s greatest achievements were only made possible by oases. Without them, the first humans who left Africa, the ones who built the Silk Road that connected Europe and Asia in ancient times, would have had a much harder time. These islands of water supported certain historical processes, like the slave trade between sub-Saharan Africa and imperial Rome, the invasions of the West by the Asian East and the expansion of Islam. Now, a group of scientists has created a world map to observe two parallel processes of which, in a near future driven by climate change, only one could remain: while some of these green spaces are expanding due to human intervention, others are shrinking from the desert’s advance. In the time, between the two, experts are clear on one thing: the future of the oases is uncertain.

Researchers at the Chinese Academy of the National Center for Research in Cairo have created what they believe to be the first world map of oases. Popularized in literature and film, the Western ideal of these topographic formations is composed of palm trees, a pool of water and caravans. The now-vanished Palmyra (the ruins of which were destroyed by Islamic State terrorists) is the prototype of this archetype. The city of date trees was the point of connection between the East and West for millennia and between the Persian and Roman empires for centuries. But the reality of oases is much more complicated.

According to the map, there are oases in 37 countries and the majority of their mass is not in Africa and its two principal deserts, the Sahara and the Namib: 77% of these green refuges are found in Asia. And, though many of them are located on the Arabian peninsula and throughout the near East, the bulk of oases are found so far north that they don’t have palm trees, and the deserts that surround them are so cold that, during the winter, temperatures drop to between -4ºF and -22°F. In fact, more than half of these fertile zones are found in central Asia and northeast China. Those within the interior of Australia (with 13.6%) and on portions of the western flank of the two American continents (at 5.02%) follow on the list. African oases only represent 4.21% of their total. These percentages allow us to better define what an oasis is: an area within an arid region, not necessarily hot, surrounded by desert, not necessarily sand, that has a reliable source of water that is not rain and is not always subterranean.

The oasis world map is by no means a static image. Its creators based it on images gathered by the European Space Agency (ESA)’s Climate Change Initiative. Supported by these satellites, it has been mapping the Earth’s surface and its different types of vegetal cover, from frozen moors to the most fertile jungles, for decades. The archive allowed the team to bring the oasis map to life and to see how oases have evolved since 1995. In fact, the movement of these green spaces is the central focus of the new study, which was published in the scientific journal Earth’s Future.

The satellite images’ history speaks of two parallel processes. On one hand, the study found that the oases, in general, grew by more than 85,000 square miles between 1995 and 2020. But at the same time, a loss of 51,853 square miles was experienced by other oases during the same period. That added up to a net growth of 33,400 square miles. In total, worldwide, there are 1.2 million square kilometers of oases.

Water is the only limiting factor that determines the existence, development and extinction of the oasis, when there’s not enough, the desert takes back the land
Dongwei Gui, researcher at the Xinjiang Institute of Geography and Ecology

“The oases are distributed throughout the world’s distinct desert regions, which means that different oases have different situations,” Dongwei Gui, researcher at the State Laboratory of Desert and Oasis Ecology at the Xinjiang Institute of Geography and Ecology and co-author of the study, said in an email. “While some in China have been able to expand thanks to the human factor (the extraction of subterranean water, for example) others in Egypt have contracted due to a lack of water,” he says. In fact, the authors say that practically all expansion has anthropogenic causes, while losses are due to the desertification process that many areas of the planet are experiencing. “Water is the only limiting factor that determines the existence, development and extinction of the oasis, when there’s not enough, the desert takes back the land that is occupied by the oasis,” adds Gui.

Xingiang is a good example. It’s the most northeastern Chinese province. With an area three times larger than Spain, nearly the same size as Mexico, it houses some of the planet’s largest oases, like Turfán, a city with more than 500,000 inhabitants. Since the Chinese government liberated its territories and land use, the region, which is among the poorest in the country, has gone through an agricultural explosion that has turned it into one of the country’s primary sources for vegetables and greens. In a certain sense, it’s repeating the history of the agricultural land in southeastern Spain. In fact, the intensification of agriculture is the primary cause of oasis expansion. This growth has also been seen in Africa, due to the artificial irrigation of lands that were previously deserts.

At the same time, the oases, integral parts of arid regions, are suffering from the impact of climate change and the desertification that it is causing. The greatest losses have taken place in the green spaces of Africa, but also in many parts of Asia. Researchers estimate that the changes to the oases have directly affected some 34 million people worldwide.

University of Alicante researcher Jaime Martínez Valderrama was recently in Xinjiang, where he collaborated on a project with some of the oasis map’s creators. He says that we often think of the oasis in the vein of those located in the Saharan or Arabian deserts, which are sustained by subterranean waters thanks to natural providence or an excavated well. “Ninety-nine percent of the world’s fresh water in a liquid state is underground,” he says. In fact, the largest aquifers are beneath the sands of the Sahara. “It’s rainwater that fell 40,000 years ago,” he says. Thanks to technology inspired by oil extraction, older traditional wells have been replaced by sophisticated pumping and extraction systems whose use is permitted to fill the demand of North African coastal megacities for grains, fruits and vegetables, but they are compromising the future of the Saharan oases. “They are no longer four palm trees, but rather real food production systems that, in these arid zones, which have a lot of sun, good temperatures and now the water they were missing, are now so attractive that they are expanding,” says Martínez, who is also a scientist at the Spanish National Research Council (CSIC)’s Arid Zone Experimental Station.

The oases of central Asia and northeast China are another matter. “They are also maintained by subterranean waters, but their primary source is snow from the mountains,” says the Spanish researcher. The region’s mountain ranges, with altitudes between 13,100 to 23,000 feet, are flanked by enormous rivers that flow into endorheic basins, meaning that they don’t end in the ocean, but rather interior lakes or deserts. These are the waters that are powering growth in China. There, they call it oasification, expansion at the cost of desert land, thanks to the exploitation of water resources.

The oases are expanding, but the water reserves on which they depend are running out
Jamie Martínez, researcher at the University of Alicate and the CSIC’s Arid Zone Experimental Station

“The oases are expanding, but the water reserves on which they depend are running out,” warns Martínez. “Not just from an abuse of resources that exceeds their ability to regenerate, but also, climate change is leading to less snow on the mountains, whose runoff is the source of the entire system,” he says. “With global warming, it’s not snowing as much, and snow is melting faster, and that is a big problem. Ultimately, you see that the factors that drive desertification are the same ones behind development. Will this kind of expansion be sustainable in a climate change scenario in which water resources are diminishing? That’s unknown.”

His sentiment is repeated by Gui, the Chinese scientist. “Without a doubt, climate change will impact the water cycle at the local and global level, bringing enormous uncertainly as to oasis sustainability. The future of oases will depend on the water situation in the context of global change and, even more importantly, on human behavior.”

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