Assessing the complex nature of climate change risks in semi-arid coastal basins

Understanding climate change risks requires moving beyond hazards alone and examining how climatic stress propagates through coupled natural and human systems. Semi-arid coastal basins are particularly exposed to these dynamics, where prolonged drought, intense human water use, and sensitive downstream ecosystems interact to shape complex and often unintended risk trajectories. Central Chile provides a compelling example, having experienced a nearly 15-year megadrought that has profoundly altered hydrological, ecological, and socio-economic conditions.In this study, we explore how climate-driven water scarcity is transmitted across semi-arid coastal basins, and how human adaptation responses reshape both short- and long-term risks. Using an integrated socio-ecological framework, we combine satellite remote sensing, hydroclimatic records, land-use and census data, and water rights information. Indicators include precipitation, streamflow and groundwater depth, standardized drought indices, vegetation dynamics derived from NDVI, urban expansion inferred from night-time lights (VIIRS), and surface water changes in small coastal lagoons quantified using NDWI.Our results reveal contrasting adaptation pathways across managed and unmanaged systems. Irrigated agriculture shows a high degree of apparent resilience, maintaining vegetation productivity during prolonged drought through intensified groundwater use and technological adaptation. However, this response is closely linked to accelerated groundwater depletion, streamflow collapse, and downstream ecological degradation, illustrating a clear case of maladaptation driven by short-term productivity gains. In contrast, natural shrublands and forests respond more directly to hydroclimatic variability, with forest systems exhibiting delayed and potentially threshold-like responses under sustained drought conditions.Coastal lagoons emerge as sentinel systems that integrate cumulative basin-scale stress. Satellite observations document a shift from persistent ocean connectivity to prolonged inlet closure during the megadrought, alongside shrinking water surfaces and signs of regime change at the land–sea interface. Overall, our findings highlight how uneven adaptation capacity and sector-specific responses can amplify cascading climate risks, underscoring the need for integrated, basin-scale adaptation strategies that explicitly consider cross-system feedbacks, ecological thresholds, and governance constraints.