Forest loss may make watersheds leakier, global study suggests

A global analysis of 657 watersheds found that forest loss and changes in forest spatial arrangement increase the share of 'young water' (precipitation that passes through a watershed within about two to three months), which reduces longer-term storage in soils and groundwater.

New research involving UBC Okanagan researchers finds that forest loss and the spatial arrangement of remaining forest patches can change how watersheds hold and release water. The study used data from 657 watersheds across six continents and was published in Proceedings of the National Academy of Sciences. Researchers focused on the fraction of "young water," defined as rain and snowmelt that moves through a watershed within roughly two to three months, as a signal of how quickly water moves. The analysis examined both the amount of forest cover and how forest patches are distributed on the landscape. Key findings: - Both forest loss and changes in forest landscape pattern were associated with higher proportions of young water, indicating faster throughflow and less storage in soils and groundwater. - In watersheds with relatively low forest cover (typically below about 40–50%), the arrangement of remaining forest patches had a strong influence on young-water fractions. - In watersheds with higher, contiguous forest cover, forest pattern had little detectable effect on water partitioning, likely because microclimate changes are muted. Summary: The study indicates that reducing forest cover tends to lower a watershed's capacity to retain water and that landscape configuration can either worsen or partly offset that effect. The authors highlight implications for forest and watershed management in regions where timber harvesting is important, but specific policy or procedural steps were not reported. Undetermined at this time.