Hydrological Insights From Combined Long‐Term Monitoring (Hydrometric and Tracer) and Modelling of Headwater Catchments in Costa Rica

Abstract

Understanding ecohydrological water partitioning and flow paths in tropical headwater systems is critical for habitat preservation and sustaining downstream water resources under increasing climatic variability and land‐use pressures. This study integrates a 13‐year (2013–2026) hydrometric and tracer monitoring dataset with ecohydrological modelling across 11 headwater catchments and spring systems spanning the Caribbean and Pacific continental gradient of north‐central Costa Rica (from 1471 to 2430 m asl). The region is characterised by strong precipitation seasonality, permeable volcanic soils, fractured volcanic aquifers and dynamic groundwater–surface water interactions. Water temperature and electrical conductivity observations reveal a relatively low thermal spatial variability (~5°C), a strong groundwater influence on stream diurnal thermal regimes and contrasting catchment responses to seasonal precipitation inputs. Stable isotope data indicate rapid streamflow response and a dominance of young water in surface systems, whereas springs exhibit damped isotopic variability consistent with longer subsurface residence times and enhanced mixing. Ecohydrological modelling in four selected catchments (Caribbean: San Rafael and El Gallito/Las Vueltas; Pacific: Ciruelas and Sacramento) demonstrates that dynamic flow paths are mainly driven by climate regimes, with deeper flow paths shaped by the volcanic subsurface structure. Overall, our findings highlight the value of long‐term, integrated multi‐tracer and hydrometric monitoring combined with ecohydrological modelling for capturing the complex and highly dynamic water partitioning behaviour of high‐elevation tropical catchments. Such a monitoring‐modelling framework helps inform water resource management and climate variability adaptation strategies in similar headwater‐dependent systems across the wet tropics.