When I was an elementary school student and first heard of “global warming”, I thought the solution to climate change was simple: just plant more trees! 🌳
While I now know there’s a great deal more complexity to the problem than that, I have always wondered what would happen if someone had tried out that little boy’s instinct.
In a recent article in Earth’s Future, scientists took a look, taking advantage of China’s massive investment over decades in planting trees around the country, “which accounted for 25% of the global net increase in leaf area [between] 2000–2017”! In particular, they found that, while they were able to impact dust storms and desertification, the rapid planting of trees had major negative impacts on underground water supplies as the massive resulting evapotranspiration (literally plants pulling water from the ground and into the air) effectively transferred that groundwater into rainwater over the Tibetan Plateau!
China, especially its Northern/Northwestern regions, have major issues with water availability and drought and it is a cosmic irony that an attempt to stop desertification, while greening much of the land, may have resulted in worsening the water condition.
It is a humbling reminder that large-scale well-intention actions may have adverse consequences and a reminder that, while we should pursue indirect avenues for mitigating climate change, there is probably no substitute for ultimately cutting down on the emissions and activities that are most directly related.
Their model shows that land restoration increased evapotranspiration by around 1.7 millimeters per year and precipitation by about 1.2 millimeters per year, yet overall water availability still went down.
The main driver was forest expansion in the humid east and large-scale restoration in the northwest and on the plateau. As deep-rooted trees pull water from the soil and release it into the air, they act a bit like giant pumps. The process cools the local surface but also ships moisture downwind, where it can fall as rain far from the place where it was originally stored.
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