Land Cover Change Drives River Flow Modifications in Central Chile

There are global concerns about the hydrological impacts of native forest loss or plantation forestry expansion, but such impacts are not well understood in zones where the El Niño Southern Oscillation (ENSO) may mask underlying land cover change effects. Soil conditions also play a crucial role, as differences in soil properties inherited from previous land uses can influence current patterns of soil degradation and hydrological responses. This study investigated these combined effects on river flow dynamics in coastal catchments of central Chile. Using a 45-year dataset (1979–2023), we found significant streamflow declines in four of five catchments, particularly in summer, where water availability is most critical. Catchments with 4%–9% native forest loss exhibited lower summer streamflow, whereas those with preserved forest (e.g., Butamalal) maintained or increased summer flows. Higher native forest fractions were associated with greater catchment-scale precipitation–streamflow ratios, as indicated by a significant precipitation × native forest interaction. In contrast, a lower PP-Q ratio was observed in basins with higher exotic plantation fractions, reflected in a significant precipitation × exotic plantation interaction (R2 = 0.46–0.77; negative slopes). ENSO phases alone explained little streamflow variability (R2 < 0.04); however, their interaction with precipitation was significant across all catchments (p < 0.001), highlighting an indirect but consistent climatic influence. These relationships likely reflect the interaction between land cover composition, legacy soil conditions, and climatic variability, but are based on monthly precipitation–streamflow responses which may mask finer scale process-responses. Our findings underscore the dominant role of land cover, particularly native forests, in shaping hydrological resilience. The results highlight the hydrological relevance of conserving existing native forest cover and promoting its recovery in strategically important areas to enhance water security under increasing climate variability and prolonged droughts.