Together natural growth, afforestation and forest disturbance, such as felling, contribute to the dynamic nature of forests. Thus to enhance forest management, water resource management and carbon sequestration, the net effect of forest changes on water yield must be better understood. Here, we conduct a global meta-analysis of 496 watersheds over 25 years to investigate the impact of forest complexity and overall changes on water yields. We classify watersheds based on the type of human disturbance, including felling and thinning, afforestation, and absence of external disturbances. We find that the runoff coefficient (ratio of annual water yield in watershed outlet to precipitation) is more sensitive to external disturbances in forests with lower ecosystem complexity compared to forests with higher complexity. In addition, we found forest natural growth may increase runoff and lead to an increased runoff coefficient decades later. Our findings highlight the importance of nature-based forest restoration, especially in regions vulnerable to water shortage.
