Assessing hydrological responses to large-scale native forest restoration as a nature-based solution in South-Central Chile under climate change

Forests play a fundamental role in regulating the hydrological cycle and providing essential ecosystem services, functions that are increasingly threatened by climate change and human activities. Chile offers a relevant context for examining the relationship between land use change and hydrological processes, given its history of landscape transformations and growing water stress in the south-central region. Under the RCP8.5 climate scenario, four forest restoration scenarios were simulated using the TETIS hydrological model. These scenarios were designed based on national policies, Nature-Based Solutions (NbS) principles, and social criteria, and applied to two sub-basins of the Imperial River in the Araucanía Region. Our findings show that the combined effects of climate change and land use change produce the largest variations in hydrological processes. Increases in forest cover led to higher evapotranspiration, particularly under exotic plantation scenarios. Although streamflow generally declines, scenarios with native forest restoration in mid-to-upper basin areas provide a buffering effect on streamflow, especially during dry seasons. Large-scale native forest restoration enhances water retention and hydrological stability, whereas plantation-dominated reforestation results in the greatest water losses, particularly in dry years. These results highlight the effectiveness of NbS-oriented native forest restoration in maintaining water security, regulating hydrological flows, and supporting climate adaptation, providing actionable guidance for watershed management and policy development in Chile.