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The Great Green Wall is a huge re-greening initiative in northern China aimed at slowing desertification. | Credit: PEDRO PARDO/AFP via Getty Images
China’s efforts to slow land degradation and climate change By planting trees and restoring grasslands, they have changed water across the country in huge, unforeseen ways, new research shows.
Between 2001 and 2020, changes in vegetation cover reduced the amount of fresh water available to people and ecosystems in the eastern monsoon region and northwestern arid region, which together make up 74 percent of China’s dry land, according to a study published Oct. 4 in the journal. Earth’s future. During the same period, water availability increased in China’s Tibetan Plateau region, which makes up the remaining landmass, the scientists found.
“We find that land cover changes redistribute water,” study co-author Aria Staalassistant professor of ecosystem resilience at Utrecht University in the Netherlands, told Live Science in an email. “China did re-greening on a massive scale in recent decades. They have actively restored thriving ecosystems, especially in the Loess Plateau. This also reactivated the water cycle.”
Three main processes move water between the Earth’s continents and the atmosphere: evaporation and transpiration carry water up, while precipitation drops it back down. Evaporation removes water from surfaces and soil, and transpiration removes water that plants have absorbed from the soil. Together, these processes are called evapotranspiration, and it fluctuates with plant cover, water availability and the amount of solar energy reaching the ground, Staal said.
“Both grasslands and forests generally tend to increase evapotranspiration,” he said. “This is particularly strong in forests, because trees can have deep roots that access water in times of drought.”
China’s largest tree-planting effort is the Great Green Wall in the country’s arid and semi-arid north. Begun in 1978, the Great Green Wall was created to slow the expansion of the desert. Over the past five decades, it has helped increase forest cover from about 10% of China’s area in 1949 to more than 25% today—an area equivalent to the size of Algeria. Last year, government officials announced that the country had finished encircling the largest vegetated desert, but would continue to plant trees to keep desertification under control.
Other large regreening projects in China include the Grain for Green Program and the Natural Forest Protection Program, which both began in 1999. The Grain for Green Program incentivizes farmers to convert farmland to forests and pastures, while the Natural Forest Protection Program prohibits logging in primary forests and promotes afforestation.
Collectively, China’s ecosystem restoration initiatives accounts for 25% of the global net increase in leaf area between 2000 and 2017.
But regreening has dramatically changed China’s water cycle, boosting both evapotranspiration and precipitation. To investigate these effects, the researchers used high-resolution evapotranspiration, precipitation and land-use change data from various sources, as well as a tracking model of atmospheric moisture.
The results showed that evapotranspiration generally increased more than precipitation, meaning some water was lost to the atmosphere, Staal said. However, the trend was not consistent across China, as winds can transport water up to 4,350 miles (7,000 kilometers) away from its source—that is, evapotranspiration in one place often affects precipitation in another.
The researchers found that forest expansion in China’s eastern monsoon region and grassland restoration in the rest of the country increased evapotranspiration, but precipitation increased only in the Tibetan Plateau region, so the other regions experienced a decrease in water availability.
“Even though the water cycle is more active, at the local scale more water is being lost than before,” Staal said.
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This has important implications for water management, as water in China is already unevenly distributed. The north has about 20 percent of the country’s water, but is home to 46 percent of the population and 60 percent of the arable land, according to the study. The Chinese government is trying to address this; however, the measures are likely to fail if the redistribution of water due to regreening is not accounted for, Staal and his colleagues argued.
Ecosystem restoration and afforestation in other countries could also affect water cycles there. “From a water resources standpoint, we have to see on a case-by-case basis whether certain land cover changes are beneficial or not,” Staal said. “It depends, among other things, on how much and where the water entering the atmosphere comes down again as precipitation.”