Evaluating anthropogenic influences on watershed hydrological dynamics in St. Croix, U.S. Virgin Islands

Introduction Land cover modifications and climate change, mainly driven by anthropogenic activities, substantially modify hydrological water partitioning. On Saint Croix, land use has shifted from native forest to sugarcane cultivation, followed by secondary forest regrowth and, more recently, rapid urbanization. Understanding its hydrological impacts is essential for strengthening watershed management and promoting sustainability. Methods The study therefore examines the implications of these transformations on stream dynamics over the past 33 years (1985–2018) using a hydrological modeling approach. Four representative periods, 1985, 1992, 2004, and 2018, were evaluated based on corresponding land use maps. Results and discussion The land use impact assessment shows increased streamflow in 1992 and 2018, linked to shrub-land and urban expansion, respectively, while a decline of up to 9.52% in 2004 corresponds to secondary forest development, particularly in the mountainous northwest area. Over the 33-year period, rising wet-season rainfall combined with expanding built-up areas resulted in notable increases in wet-season streamflow by 25% in Jolly Hill and 76.6% in the Bethlehem watersheds. Streamflow behavior indicates that Jolly Hill and upper Bethlehem catchment respond similarly, reflecting parallel land use trajectories, whereas the mid- and downstream portions of Bethlehem exhibit a sustained increase in streamflow. Although streams in St. Croix are non-perennial and small absolute changes can yield large percentage increases, the observed rise in flow remains indicative of amplified runoff generation. The study, overall, quantifies impacts of land cover and climate changes on flow dynamics providing evidence-based insights to inform water and watershed management in the island.