In the desert, where water sources are extremely scarce, there occasionally appear places with abundant water, usually forming oases.
Oases create a significant ecological community in the vast desert, maintaining a microclimate and ecological landscape distinct from the desert.
In arid regions, ensuring sources of drinking water and agricultural water is crucial, which is why many historical settlements were established around oases.
In these oases, people grow grains like wheat and drought-resistant fruit trees such as dates and grapes, forming oasis agriculture.
Depending on the water source, oases can be classified into spring-fed oases, foothill oases, exorheic river oases, and artificial oases.
Spring-fed oases are sustained by surface or shallow groundwater sources.
Digging wells can tap into the underground aquifers in the desert (unconfined groundwater or confined groundwater).
Although unconfined groundwater does not naturally flow to the surface, it can be directly used as fresh water after being accessed through wells due to its low salinity.
In contrast, confined groundwater, due to the pressure from the surrounding layers, will gush out when there is a breach in the layer.
However, this water usually has a high salinity, making it unsuitable for drinking or agricultural use.
Foothill oases utilize the precipitation from the high mountains surrounding the desert.
In the mountainous regions on the edges of deserts, rainfall from the mountains flows into the desert at the foothills and is stored underground.
Foothill oases form by utilizing these groundwater sources, usually located at the desert’s periphery, at the foot of the mountains.
For example, the fringes of China’s Tarim Basin are filled with such oases.
The Tarim Basin is surrounded by the Tianshan, Kunlun, and Karakoram mountains. The snowmelt from these mountains nourishes the basin’s outskirts, forming various oasis cities.
These oasis cities have been significant nodes on the Silk Road since ancient times, serving roles in supply, trade, and rest.
Although mountain precipitation can serve as a water source for foothill oases, the water collection is typically limited to the alluvial fan area at the valley openings.
In arid regions, to prevent rapid evaporation of surface water, locals invented underground water channels, such as China’s "Karez." This type of underground water system is known as Qanat in Iran, Qarez in Afghanistan, and Fogara in North Africa.
Exorheic river oases are formed when external rivers flow into desert areas.
The river's water source typically comes from upstream rainfall and snowmelt. The most typical example is the Nile Delta in Egypt.
Egypt has a tropical desert climate, but the Nile provides ample water, making oasis agriculture highly developed, even giving rise to ancient Egyptian civilization.
In Central Asia, rivers originating from the high mountains of the eastern Pamir plateau form exorheic river oases.
Uzbekistan’s Samarkand, Tashkent, and Bukhara are typical exorheic river oases.
These areas underwent massive development during the Soviet era, using water from the Amu Darya and Syr Darya rivers for agricultural irrigation, cultivating crops like cotton.
With modern technology, places previously hard to access water can now form stable water sources through artificial means, creating new cities in the desert, known as artificial oases.
Artificial oases ensure water sources by extensively pumping groundwater with electricity and water pumps or by constructing large dams.
An example is the irrigation agriculture in the central plains of the United States, utilizing groundwater.
The Ogallala Aquifer beneath the Great Plains provides ample water to support large-scale agricultural production.
Meanwhile, Las Vegas, located in the southern desert of Nevada, relies on the water resources and hydroelectric power from the Hoover Dam, developing into a resort city focused on tourism.
Whether naturally formed spring-fed oases, foothill oases, exorheic river oases, or artificial oases created through modern technology, oases play a crucial role in arid and semi-arid regions.
They not only provide valuable water resources and agricultural production conditions for humans but also serve as important nodes for cultural exchange and civilization development.
With continuous technological advancement and increased human adaptability to the environment, future oases may emerge in more desert areas, offering greater possibilities for human societal development.
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