Preface. We’ll need a lot of forests in the future when wood once again becomes our main source of energy and infrastructure as it was before fossil fuels. But planting more trees an backfire and have unintended consequences

Alice Friedemann  www.energyskeptic.com  Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”.  Women in ecology  Podcasts: WGBH, Financial Sense, Jore, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity,  Index of best energyskeptic posts

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2025 China Planted 78 Billion New Trees—and Seriously Messed Up Its Water Cycle. Popular Mechanics

China began growing the Three-North Shelterbelt, or “The Great Green Wall,” in 1978 as an effort to combat soil erosion and decrease desert storms. The project, the country’s state-sponsored media announced, was finally complete as of last year.

According to Reuters, China grew 116,000 square miles of trees, increasing the country’s total forest coverage from 10 percent in 1949 to roughly 25 percent in 2024. But a new study published in the journal Earth’s Future, shows that all those additional trees (roughly 78 billion since the early 80s, by some estimates) come with some unforeseen consequences for China’s water distribution.

between 2001 and 2020, increased vegetation reduced water resources in both the eastern monsoon region and the northwestern arid region. That’s a big deal, considering these areas make up roughly 74% of China’s total land area

According to the study, regreening efforts like the Great Green Wall—along with other tree-planting initiatives, such as Grain for Green Program and the Natural Forest Protection Program, with both started in 1999—have increased evapotranspiration, which is a portmanteau of evaporation and transpiration (the process through which plants release water vapor through tiny pores known as stomata).

“These shifts caused changes in precipitation, directing more moisture to the Tibetan Plateau, which saw an increase in water availability,” the authors wrote. “In contrast, eastern and northwestern China experienced a decrease in water availability, with the northwest losing the most due to substantial moisture moving to the Tibetan Plateau.”

China’s water availability isn’t conveniently distributed for its population. According to the study, the country’s northern regions contain roughly 46 percent of its population and more than half of the arable land, but only 20 percent of water availability.

 

Bentley, L., et al. 2020. Partial river flow recovery with forest age is rare in the decades following establishment. Global Change Biology.

River flow is reduced in areas where forests have been planted and does not recover over time, a new study has shown. Rivers in some regions can completely disappear within a decade. This highlights the need to consider the impact on regional water availability, as well as the wider climate benefit, of tree-planting plans.

“Reforestation is an important part of tackling climate change, but we need to carefully consider the best places for it. In some places, changes to water availability will completely change the local cost-benefits of tree-planting programmes,” said Laura Bentley, a plant scientist in the University of Cambridge Conservation Research Institute, and first author of the report.

Planting large areas of trees has been suggested as one of the best ways of reducing atmospheric carbon dioxide levels, since trees absorb and store this greenhouse gas as they grow. While it has long been known that planting trees reduces the amount of water flowing into nearby rivers, there has previously been no understanding of how this effect changes as forests age.

The study looked at 43 sites across the world where forests have been established, and used river flow as a measure of water availability in the region. It found that within five years of planting trees, river flow had reduced by an average of 25%. By 25 years, rivers had gone down by an average of 40% and in a few cases had dried up entirely. The biggest percentage reductions in water availability were in regions in Australia and South Africa.

“River flow does not recover after planting trees, even after many years, once disturbances in the catchment and the effects of climate are accounted for,” said Professor David Coomes, Director of the University of Cambridge Conservation Research Institute, who led the study.

Published in the journal Global Change Biology, the research showed that the type of land where trees are planted determines the degree of impact they have on local water availability. Trees planted on natural grassland where the soil is healthy decrease river flow significantly. On land previously degraded by agriculture, establishing forest helps to repair the soil so it can hold more water and decreases nearby river flow by a lesser amount.

Counterintuitively, the effect of trees on river flow is smaller in drier years than wetter ones. When trees are drought-stressed they close the pores on their leaves to conserve water, and as a result draw up less water from the soil. In wet weather the trees use more water from the soil, and also catch the rainwater in their leaves.

“Climate change will affect water availability around the world,” said Bentley. “By studying how forestation affects water availability, we can work to minimise any local consequences for people and the environment.”