China has planted so many trees it’s changed the entire country’s water distribution
China’s efforts to slow land degradation and climate change By planting trees and restoring grasslands, waters were moved across the country in significant and unanticipated ways, new research shows.
Between 2001 and 2020, changes in vegetation cover reduced the amount of fresh water available to humans and ecosystems in the eastern monsoon region and the arid northwest region, which together account for 74% of China’s land area, according to a study published October 4 in the journal. The future of the Earth. During the same period, water availability increased in China’s Tibetan Plateau region, which makes up the remaining area, the scientists found.
Three main processes move water between Earth’s continents and the atmosphere: evaporation and transpiration carry water upward, while precipitation moves it downward. Evaporation removes water from surfaces and soils, and transpiration removes water that plants have absorbed from the soil. Together, these processes are called evapotranspiration, and it fluctuates depending on vegetation cover, water availability and the amount of solar energy that reaches the land, Staal said.
“Grasslands and forests generally tend to increase evapotranspiration,” he said. “This is particularly important in forests because trees can have deep roots that access water in drought.”
China’s largest tree-planting effort is the Great Green Wall, located in the country’s arid and semi-arid north. Launched in 1978, the Great Green Wall was created to slow the expansion of deserts. Over the past five decades, it has helped increase forest cover from about 10% of China’s land 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 ringing its largest desert with vegetation, but would continue planting trees to contain desertification.
Other major regreening projects in China include the Grain for Green program and the Natural Forest Protection Program, both of which started in 1999. The Grain for Green program incentivizes farmers to convert agricultural land into forests and grasslands, while the Natural Forest Protection Program prohibits logging in primary forests and promotes afforestation.
Collectively, China’s ecosystem restoration initiatives represent 25% of the global net increase in leaf area between 2000 and 2017.
But regreening has dramatically changed China’s water cycle, increasing both evapotranspiration and precipitation. To study these impacts, the researchers used high-resolution data on evapotranspiration, precipitation and land-use change from a variety of sources, as well as an atmospheric humidity monitoring model.
The results showed that evapotranspiration overall 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 carry water. up to 4,350 miles (7,000 kilometers) far from its source, meaning evapotranspiration in one location often affects precipitation in another.
The researchers found that the expansion of forests in China’s eastern monsoon region and the restoration of grasslands in the rest of the country increased evapotranspiration, but precipitation only increased in the Tibetan Plateau region, so other regions experienced a decline in water availability.
“Even though the water cycle is more active, on a local scale more water is being lost than before,” Staal said.
This has important implications for water management, as water in China is already unevenly distributed. The north has about 20% of the country’s water but is home to 46% of the population and 60% of the arable land, according to the study. The Chinese government is trying to solve this problem; However, these measures will likely fail if water redistribution due to regreening is not taken into account, Staal and colleagues argued.
Ecosystem restoration and afforestation in other countries could also affect water cycles there. “From a water resources perspective, we need 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 that enters the atmosphere comes back down as precipitation.”
