Anthropogenic and climatic impacts on hydrological processes: a multiple approach on the role of groundwater in complex watersheds in the state of São Paulo

Author(s)

Lucas Vituri Santarosa

• Document type: Doctoral Thesis
• Press: Rio Claro. 2021-01-08.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Geociências e Ciências Exatas. Rio Claro
• Defense date: 2020-12-11
• Advisor: Didier Gastmans

Abstract

The increasing global pressure on water resources, under natural and anthropogenic conditions, requires integrated multidisciplinary approaches to cope with scientific and social issues. Assessing the magnitude of the impacts of anthropic actions and climatic variations on hydrological processes is crucial to inform the water resources managers about the actions to be performed and minimize the negative effects in social, economic, or environmental functions of water. For this, modeling methods applied to hydrological (fluviometry and pluviometry) and isotopic (2H and 18O) data in the temporal and spatial dimensions were combined, to understand the hydrogeological regime of the baseflow and evaluate its function in water resilience. The study was conducted in a scenario of climatic variations and anthropogenic activities in the Piracicaba-Capivari-Jundiai (UGRHI 5 - PCJ) and Tietê-Jacaré (UGRHI 13 - TJ) basins. The results reveal that the water resilience of the studied basins is controlled by the direct interaction of the rain regime with the hydrogeological domains. In the crystalline domain, where most of the PCJ basins are located, the storage capacity of the water surplus in the wet period is less, which increases the importance of the rains for generating direct runoff and composing the streamflow. In the sedimentary domain, which includes part of the PCJ basins and the TJ basins, they have greater storage capacity in their aquifers, where the baseflow provides greater seasonal stability of the streamflow. The modeling of the data shows that the annual stramflow are maintained by a portion of groundwater that varies from 50 to 70% of the total volume in the crystalline domain, while in the sedimentary the contribution varies from 70 to 80%. It is concluded that the hydrological regime in the crystalline domain is more dependent on surface waters and is more vulnerable to prolonged droughts, while the sedimentary domain has greater water security. The vulnerability of the PCJ basins to reductions in rainfall volumes and anthropogenic activities reveal negative variations in streamflow and minimum storage, also reflected in changes in isotopic signs. Less accentuated situation in the TJ basins, but with attention to the exploitation of aquifers. However, it is recommended that managers take an adaptive approach and expand the monitoring capacity of the basins, both surface and underground water resources. The potential of stable H and O isotopes is highlighted as a complementary methodology to conventional monitoring, capable of describing seasonal climatic and anthropogenic processes in a heterogeneous hydrogeological spatial context. This study highlights the issue of water resilience in a region of great economic and social importance in Brazil and contributes to the scientific framework aimed at isotopic application in large basins. (AU)

• FAPESP's process: 17/13576-9 - STABLE ISOTOPES (d2H and d18O): UNVEILING THE ORIGINS OF SURFACE WATER IN SÃO PAULO STATE WATERSHEDS
• Grantee: Lucas Vituri Santarosa
• Support Opportunities: Scholarships in Brazil - Doctorate