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The Great Green Wall is a large-scale greening initiative in northern China aimed at mitigating desertification. | Photo credit: Pedro Pardo/AFP, Getty Images
China’s efforts to mitigate land degradation climate change New research shows that reforestation and grassland restoration have diverted water across the country in huge, unforeseen ways.
Changes in vegetation cover between 2001 and 2020 reduced the amount of freshwater available to humans and ecosystems in the eastern monsoon zone and northwest arid zone, which together account for 74% of China’s land area, according to a study published in the journal on October 4. Earth’s future. Scientists found that during the same period, water availability increased in China’s Tibetan Plateau region, which makes up the remaining land area.
“We found that land cover changes redistribute water,” study co-author Ari Starran assistant professor of ecosystem resilience at Utrecht University in the Netherlands, told LiveScience in an email. “China has already done this Large-scale greening past decades. They actively restore thriving ecosystems, especially on the Loess Plateau. This also reactivates the water cycle. “
There are three main processes by which water moves between Earth’s continents and the atmosphere: evaporation and transpiration bring water to an ascending position, while precipitation brings water back to a descending position. Evaporation removes water from surfaces and soil, and transpiration removes water that plants absorb from the soil. These processes, collectively known as evapotranspiration, fluctuate with plant cover, available water and the amount of solar energy reaching the land, Starr said.
“Grasslands and forests generally increase evapotranspiration,” he said. “This is especially true in forests because trees can have very deep roots that can access water during dry times.”
China’s largest tree-planting campaign is the Great Green Wall in the country’s arid and semi-arid northern region. Construction of the Great Green Wall began in 1978 to slow the expansion of the desert. Over the past 50 years, China’s forest coverage has increased from about 10% in 1949 to more than 25% Today – an area the size of Algeria. Last year, government representatives announced that the country had completed vegetating its largest desert, but would continue to plant trees to control desertification.
Other large-scale greening projects in China include the conversion of farmland into forests and natural forest protection projects started in 1999. The return of farmland to forests project encourages farmers to return farmland to forests and grasslands, while the natural forest protection project prohibits logging of virgin forests and promotes afforestation.
Overall, China’s ecosystem restoration initiatives 25% Global net increase in leaf area between 2000 and 2017.
But afforestation has dramatically changed China’s water cycle, increasing evapotranspiration and precipitation. To study these effects, the researchers used high-resolution evapotranspiration, precipitation and land-use change data from various sources, as well as atmospheric moisture tracking models.
Starr said the results showed that the overall increase in evapotranspiration was greater than the increase in precipitation, meaning some water was lost to the atmosphere. However, this trend is not consistent across China because wind can transport water Up to 4,350 miles (7,000 kilometers) Far from the source – this means that evapotranspiration in one place often affects precipitation in another place.
The researchers found that forest expansion in eastern China’s monsoon region and grassland restoration in other parts of the country increased evapotranspiration, but only precipitation increased in the Tibetan Plateau, so water availability elsewhere declined.
“Although the water cycle is more active, on a local scale more water is being lost than before,” Starr said.
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This has important implications for water management, as water is already unevenly distributed in China. Research shows that the northern region has about 20% of the country’s water resources, but 46% of the country’s population and 60% of its arable land. The Chinese government is working to address this problem; however, Starr and his colleagues believe that these measures may fail if the reallocation of water caused by regreening is not taken into account.
Ecosystem restoration and reforestation in other countries may also affect the water cycle there. “From a water resources perspective, we need to look at it on a case-by-case basis as to whether certain land cover changes are beneficial,” Starr said. “It depends on how much and where the water that enters the atmosphere falls back down as precipitation.”