Reforestation increases water inequality under low warming but reduces water availability under high warming

Land management plays a critical role in climate mitigation and local water security. Reforestation, as a key land management strategy, is widely implemented to sequester carbon, and it also alters local water availability through biophysical effects. However, how the same reforestation activity affects water availability under different climate states remains unclear, a gap critical for adaptive land management and water policy. Here, we show that the hydrological consequences of reforestation depend on the background climate state. Using Earth system model simulations, we find that under a low-warming scenario, reforestation causes an insignificant increase in global mean water availability but increases spatial inequality (stronger wetting over wet regions). In contrast, under a high-warming scenario, reforestation reduces global water availability while weakening spatial inequality (drying over wet regions). A moisture budget analysis attributes these differences to circulation responses in wet regions. Our findings reveal that climate context shapes reforestation outcomes, providing practical insights for policymakers designing climate-adaptive land management strategies.