This chapter explores the role of hydrological processes as sentinel indicators of climate change, emphasizing the time of appearance of anomalies in fog, groundwater, and vegetation dynamics in Mediterranean and semi-arid regions of Chile. By analyzing case studies on the spatial-temporal variability of fog, groundwater storage, and primary productivity, we explore how these variables signal changes in the hydrological cycle under increasing climatic stress. Groundwater availability and fog frequency offer crucial insights into water resource dynamics, while changes in phenology reveal vegetation responses to prolonged drought and heat waves. The findings of these original studies contribute to improving drought management strategies and highlight the importance of early detection of hydrological anomalies and ecosystem resilience in regions highly vulnerable to climate variability.