The Large-Scale Effect of Forest Cover on Long-Term Streamflow Variations in Mediterranean Catchments of Central Chile

Forest ecosystems play an important role in surface and subsurface runoff, as well as the availability of water. Therefore, it is important to have a greater understanding of the interactions between forests and the production of water in watersheds. In this sense, this study evaluates the long-term effect of native forests and forest plantations on streamflow variations in central Chile, an unusual climatic area characterized by a well-marked annual cycle with dry summers and wet winters. Thus, the temporal pattern of monthly streamflow was evaluated for mean flow (Qmean), maximum flow (Qmax), and minimum flow (Qmin) in 42 large watersheds. Each series of monthly streamflow data was QA/QC, and then evaluated using the Mann–Kendall’s non-parametric statistical test to detect temporal variations between 1994 and 2015. In addition to the previous analysis, the monthly series were grouped into wet seasons (April–September) and dry seasons (October–April), to determine if there were any significant differences within the annual hydrological cycle. The areas covered with native and forest plantations and their relative changes were evaluated for each catchment through the relationship between streamflow variations and forest cover indicators. Results suggest that streamflow variations are positive and significant when more forest cover exists. The intra-catchment relationships observed during dry seasons for both species revealed the significant role of native forests and mixed masses as key ecosystems for the conservation of long-term streamflow variations in Mediterranean catchments of central Chile. These findings encourage an urgent need to create highland afforestation programs on degraded areas of central Chile, to maximize water storage in a region that is quickly drying out due to unsustainable water and land use management practices and the effects of global warming.