Stable isotopes reveal groundwater to river connectivity in a mesoscale subtropical watershed

The Corumbatai River basin (Sao Paulo, Brazil) has a critical situation regarding water availability due to the intensive use to support agriculture and urbanization, requiring scientific information to face water demand. The aim of this study is to present a hydrological characterization based on the analysis of seasonal isotope variations (rainfall, groundwater, and surface water) and hydrometric data. Results indicate that baseflow contribution varies from 50 % to 70 % of the total flow, and water isotopic composition denotes a seasonal regime marked by the mixing of surface and groundwater in the wet period and groundwater discharge during the dry season. The results presented indicated the strong seasonal connection between atmospheric inputs and water movement across the basin, which poses an urgent need to diversify monitoring methods and create feasible regional and political regulations to control the effects on basin water resilience in the face of climate change and growing demand.

Automated summary

The Corumbatai River basin in Sao Paulo, Brazil, is facing a critical situation in water availability due to intensive use for agriculture and urbanization. The study findings indicate that baseflow contribution varies from 50% to 70% of the total flow, with a seasonal regime of mixing surface and groundwater during the wet season and groundwater discharge in the dry season. It highlights the urgent need for diversified monitoring methods and feasible regional and political regulations to control the impacts on basin water resilience in response to climate change and increasing demand.