The world's oases grew 85,000 square miles in some places and shrank 52,000 square miles elsewhere, due to desertification, a new Earth's Future study finds. With most of the growth due to artificial oasis expansion projects, water scarcity and climate change will likely lead to net losses in the future. Credit: Sergey Pesterev/unsplash
By the numbers, from 1995 to 2020:
- Oases gained 85,000 square miles, mostly from artificial expansion projects
- Oases lost 52,000 square miles from desertification and water scarcity
- Oases gained a net area of about 33,400 square miles, but that mostly artificial growth is not sustainable
Oases are important habitats and water sources for dryland regions, sustaining 10% of the world's population despite taking up about 1.5% of land area. But in many places, climate change and anthropogenic activities threaten oases' fragile existence. New research shows how the world's oases have grown and shrunk over the past 25 years as water availability patterns changed and desertification encroaches on these wet refuges.
"Although the scientific community has always emphasized the importance of oases, there has not been a clear map of the global distribution of oases," said Dongwei Gui, a geoscientist at the Chinese Academy of Science who led the study. "Oasis research has both theoretical and practical significance for achieving United Nations Sustainable Development Goals and promoting sustainable development in arid regions."
The study found that oases around the world grew by more than 220,149 square kilometers (85,000 square miles) from 1995 to 2020, mostly due to intentional oasis expansion projects in Asia. But desertification drove the loss of 134,300 square kilometers (51,854 square miles) of oasis over the same period, also mostly in Asia, leading to a net growth of 86,500 square kilometers (about 33,400 square miles) over the study period.
The findings highlight the risk climate change and anthropogenic stressors pose to these wet sanctuaries and can inform water resource management and sustainable development in arid regions. The study was published in the AGU journal Earth's Future, which publishes interdisciplinary research on the past, present and future of our planet and its inhabitants.
The birth and death of an oasis
Oases are important sources of water for humans, plants and animals in the world's drylands, supporting a majority of productivity and life in deserts. They form when groundwater flows and settles into low-lying areas, or when surface meltwater flows downslope from adjacent mountain ranges and pools. The existence of an oasis depends primarily on having a reliable source of water that is not rainfall. Today, oases are found in 37 countries; 77% of oases are located in Asia, and 13% are found in Australia.
Gui and his co-investigators wanted to understand the global distribution and dynamic changes of oases and see how they respond to a changing environment, such as variations in climate, water resources and human activities. Using data from the European Space Agency's Climate Change Initiative Land Cover Product, the team categorized the land surface into seven categories: forest, grassland, shrub, cropland, water, urban and desert.
The researchers used satellite data to look for green, vegetated areas within dryland areas, indicating an oasis, and tracked changes over 25 years. Changes in the greenness of vegetation indicated changes in land use and oasis health, the latter of which can be influenced by both human activity and climate change. They also looked at changes in land surface type to find conversions of land use.
The researchers found that global oasis area increased by 220,800 square kilometers (85,251 square miles) over the 25-year timeframe. Most of that increase was from humans intentionally converting desert land into oases using runoff water and groundwater pumping, creating grasslands and croplands. The increase was concentrated in China, where management efforts have contributed more than 60% of the growth, Gui said. For example, more than 95% of the population in China's Xinjiang Uygur Autonomous Region lives within an oasis, motivating conservation and a 16,700 square kilometer (6,448 square mile) expansion of the oasis, Gui said.
Countering human efforts to expand oases, desertification contributed to oasis loss. Worldwide, the researchers found there was a loss of more than 134,000 square kilometers (51,738 square miles) of oasis land over the past 25 years. The researchers estimate that changes to oases have directly affected about 34 million people around the world.
Overall, between gains and losses, oases had a net growth of 86,500 square kilometers (33,397 square miles) from 1995 to 2020 - but most gains were from the artificial expansion of oases, which may not be sustainable in the future.
Long-term oasis sustainability
The study highlighted ways to sustain healthy oases, including suggestions for improving water resource management, promoting sustainable land use and management and encouraging water conservation and efficient use. These efforts are especially important as the climate continues to change, Gui said.
Humans' over-exploitation of dwindling groundwater can limit oasis sustainability, as well as long-term glacier loss. While higher temperatures increase glacier melt, temporarily boosting oases' water supplies, "as glaciers gradually disappear, the yield of meltwater will eventually decrease, leading to the shrinkage of oases once again," Gui said.
International cooperation plays a crucial role in oasis sustainability, Gui said.
"Due to the unique mechanism of oasis formation, a river basin often nurtures multiple oases across several countries, making transboundary cooperation key to addressing water scarcity and promoting sustainable development," he said.
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Notes for journalists:
This study is published in Earth's Future, an open-access AGU journal. Neither this press release nor the study is under embargo. View and download a pdf of the study here.
Paper title:
"Distribution and growth drivers of oases at a global scale"
Authors:
- Bochao Cui, Dongwei Gui (corresponding author), State Key Laboratory of Desert and Oasis Ecology, Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Xinjiang, China; Cele National Station of Observation and Research for Desert Grassland Ecosystem in Xinjiang, Cele, China; and University of Chinese Academy of Sciences, Beijing, China
- Qi Liu, Yunfei Liu, State Key Laboratory of Desert and Oasis Ecology, Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Xinjiang, China; Cele National Station of Observation and Research for Desert Grassland Ecosystem in Xinjiang, Cele, China
- Sameh Kotb. Abd-Elmabod, State Key Laboratory of Desert and Oasis Ecology, Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Xinjiang, China; Soils and Water Use Department, Agricultural and Biological Research Institute, National Research Centre, Cairo, Egypt; and Agriculture and Food Research Council, Academy of Scientific Research and Technology, Cairo, Egypt
- Binbin Lu, School of Remote Sensing and Information Engineering, Wuhan University, Wuhan, China
Related research of interest:
Drying and water loss threaten green areas in China's drylands. Earth's Future, March 2024
Rapid oasis expansion, increased irrigation water use, and biomass loss in China. Earth's Future, March 2024
Water availability in China's oases significantly decreased from 1987 to 2017. Earth's Future, April 2023.
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