Reforestation at
a significant enough scale changes weather and precipitation patterns. A new
paper published in the journal Earth’s Future shows that China’s Great Green
Wall initiative of planting billions of trees over the past couple of decades
has significantly changed local and regional weather and precipitation patterns
and evapotranspiration rates. Planting more trees to induce more rainfall is
known as reforestation rainfall. In general, deforestation reduces rainfall,
and reforestation increases it.
New research published in the
journal Earth’s Future shows that the country’s reforestation effort to slow
land degradation and fight climate change has also reshaped its water supply
and local hydrologic cycles “in surprising, and sometimes uneven, ways.”
More specifically, it changed evapotranspiration rates, which led to changes in
water cycles. Evapotranspiration is simply the release of moisture from leaves
to the atmosphere.
Northern China is arid, and
previous deforestation has led to increases in desertification. The Great Green
Wall has been deemed successful in slowing desertification. The paper studies
the period from 2001 to 2020, the period when many of the trees were planted,
although reforestation projects began there in the 1990s. What was perhaps
unexpected was where the precipitation changes occurred. Meteorologist Jennifer
Gray writes:
“…between 2001 and 2020, freshwater availability dropped
in China’s eastern monsoon region and northwestern arid region, but increased
over the Tibetan Plateau.”
“Trees can grab water from much deeper into the earth,
and so it’s going to release all of that moisture into the atmosphere, even in
places where it is not raining,” Gray said.
“The atmosphere and the winds can actually transport
moisture more than 4,000 miles,” Gray explained. “So if you plant trees in one
area that doesn’t mean that that’s exactly where it’s going to rain.”
The water was distributed
unevenly, and some places actually got drier.
“While re-greening an area has tremendous amounts of
benefits for the environment and the entire planet, it’s the local people that
actually are going to see the consequences, whether that’s pro or con,” Gray
said.
Gray also noted that the
study is both encouraging and cautionary.
According to an article for
Petsnpals by Julie Majid:
“Stretching from Xinjiang through Inner Mongolia to
Heilongjiang, the Three North Shelterbelt Project reshaped millions of
hectares. Entire counties converted open land into forest belts meant to block
wind and trap soil. The scale was continental.”
“Farmers noticed changes before statisticians did. Rains
came later, sometimes heavier, sometimes missing critical planting windows. The
problem was not drought everywhere, but unpredictability.”
“Climate data from northern China showed altered
seasonal rainfall distribution. Summer precipitation clustered into fewer, more
intense events in some regions, while spring rains weakened. These shifts
became clearer as forest cover expanded, as reported by Science, complicating
long standing assumptions about land and sky behaving independently.”
“Deep soil layers showed long term drying beneath
forests. Trees accessed water faster than recharge could replace it. Over time,
reduced soil moisture limited later evaporation, shifting when and where rain
could form. The land looked restored, but its hydrology had fundamentally
changed.”
Planting trees with large
water demands can deplete soil moisture. Thus, species selection is an
important part of optimizing the process and mitigating problems. Planting
trees with high water demands can deplete groundwater as it can exceed recharge
rates, eventually affecting local water wells.
Another risk noted is that
reforestation can change monsoon patterns, which can potentially have drastic
effects on rainfall patterns. Another effect was the reduction of airborne
dust, which is most beneficial. However, dust can affect cloud formation, so
its decrease could lead to less rain in some areas. She sees reforestation as a
way of manipulating the climate, which I would call geoengineering. Models and
simulations should be adjusted based on the new data provided by the study. In
addition, she gives some recommendations:
“Future projects may need different species mixes, lower
planting density in water limited zones, and tighter monitoring of moisture
budgets. Restoration will likely succeed best when forestry, hydrology, and
meteorology plan together, because rainfall is not just something forests
receive, it is something forests can influence.”
The study compares natural forests and planted forests across China. It uses the metrics of hydraulic safety and hydraulic efficiency.
The study concluded that, in general, planted
forests had higher hydraulic safety but lower hydraulic efficiency. However,
several other variables could change that relationship on the local level.
This is an important study
that can be a guide for other reforestation impact studies in the future.
References:
China
planted billions of trees ... and accidentally moved its rain. Jenn Jordan. The
Weather Channel. January 21, 2026. China
planted billions of trees ... and accidentally moved its rain
Weather
Words: Reforestation Rainfall: Reforestation rainfall refers to the phenomenon
where planting more trees can lead to more rainfall. Jennifer Gray. The Weather
Channel. April 24, 2025. Weather
Words: Reforestation Rainfall | Weather.com
Climate-Driven
Hydraulic Traits Shift in Natural and Planted Forests: Patterns, Drivers, and
Future Acclimation. Yan Bai, Yujie Hu, Yanlan Liu, Kailiang Yu, Xiangzhong Luo,
Liyao Yu, Lei Tian, and Jianping Huang. Earth’s Future. Volume14, Issue1. January
2026. Climate‐Driven
Hydraulic Traits Shift in Natural and Planted Forests: Patterns, Drivers, and
Future Acclimation - Bai - 2026 - Earth's Future - Wiley Online Library
China
accidentally altered its rainfall after planting billions of trees. Julie Majid.
Pets n Pals. January 29, 2026. China
accidentally altered its rainfall after planting billions of trees
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