A new study from the Chinese Academy of Sciences shows that planting trees can either increase or decrease water availability depending on how much the climate warms. Under mild warming, forests slightly boost water supply. Under high warming, the same forests drain more water than rain can replace, shrinking total water availability. The effect flips based on warming level, not tree count. The research used climate simulations to compare the same large-scale reforestation under two futures. In a low-emission scenario, water supply increased modestly, mostly in already-wet regions. In a high-emission scenario, water supply dropped globally. The difference came from how heat changes atmospheric circulation and moisture movement. For carbon offset programs and reforestation pledges, the study suggests location and timing matter as much as tree count. A forest that helps fill reservoirs in one climate could deplete them in another. Policymakers and project developers may need to factor in future warming when planning tree-based carbon removal.
