China Planted an Estimated 78 Billion Trees — And Reshaped Its Water Cycle

China’s massive tree‑planting campaigns have dramatically increased green cover across the country — but a new study shows they have also changed regional water cycles in surprising ways. Researchers say billions of trees shifted atmospheric moisture, boosting water in some regions while reducing it in others.

What the study examined

The research, published in Earth’s Future and led by teams from Tianjin University, China Agricultural University and Utrecht University, analyzed land-cover and vegetation change from 2001 to 2020. It evaluated how large-scale regreening efforts — including the long-running Three‑North Shelterbelt (the "Great Green Wall") and national programs launched in 1999 such as Grain for Green and the Natural Forest Protection Program — affected evapotranspiration and precipitation patterns.

Evapotranspiration and atmospheric moisture

Evapotranspiration (the combined effect of evaporation and plant transpiration) rose as more trees and woody vegetation were planted. Transpiration occurs when plants release water vapor through tiny leaf pores called stomata. The increase in evapotranspiration altered the distribution of atmospheric moisture: more water vapor was transported to the Tibetan Plateau, while eastern monsoon regions and northwestern arid zones experienced declines in local water availability.

Regional winners and losers

The Tibetan Plateau gained moisture and saw increases in water availability. By contrast, eastern China’s monsoon areas and the northwestern arid region lost surface water availability, with the northwest suffering the largest net decline as moisture was redirected away.

Scale of planting

To give scale to the effort, Reuters reported that China added about 116,000 square miles of forest, raising national forest cover from roughly 10% in 1949 to about 25% by 2024. Some estimates place the total number of trees planted since the early 1980s at roughly 78 billion.

Land‑cover transitions matter

The study also shows that different kinds of land‑cover change have different effects. For example, converting grassland to forest increased local evapotranspiration and precipitation but often reduced net water availability because more moisture returned to the atmosphere. Converting cropland to grassland or other transitions produced distinct hydrological outcomes as well.

Why this matters for people and food

China’s water and population are unevenly distributed: northern regions contain about 46% of the population and more than half of the country’s arable land, yet hold only roughly 20% of the national water availability. Changes to regional hydrology therefore have direct implications for agriculture, livelihoods and water security.

“Our findings highlight that land cover changes can redistribute water resources between regions,” the authors write. “Understanding these effects is crucial for planning sustainable land and water management in China.”

Policy implications

The study’s authors recommend that future reforestation and land‑management programs explicitly consider hydrological consequences. Thoughtful species selection, placement of plantings, and integrated water‑land planning can help maximize ecological benefits while minimizing unintended water stress for vulnerable regions.

Bottom line: Restoring forests brings real benefits for erosion control, carbon storage and biodiversity — but large‑scale tree planting can also alter where water falls and accumulates. Policymakers should factor these effects into regional planning to avoid aggravating water shortages even as forest cover expands.