Serial droughts and loss of hydrologic resilience in a subtropical basin: The case of water inflow into the Cantareira reservoir system in Brazil during 2013-2021

Study region: Southeastern Brazil, with emphasis on the Jaguari River basin, the main tributary of the Cantareira system. Study focus: We examined the basin hydroclimate variability, especially along the historical meteorological droughts between 2013 and 2021, and the hydrologic response to negative disturbances in rainfall. Field and satellite measurements of rainfall, flow, soil moisture, and water storage were used to assess the hydroclimate variability and to validate the hydrological model. Our hypothesis is that a good model performance on these validated variables improve our confidence in the representation of aquifer storage and recharge. We also estimated the long-term elasticity of flow to precipitation using the entire analysis period (27 years), and compared to the elasticity in along the serial droughts from 2017 to 2021. New hydrological insights for the region: Results show that the serial meteorological droughts were very likely unprecedented in the last 70 years, leading to hydrologic impacts over regional scale. We estimated a decrease of 6.4 mm y-1 in the soil moisture and a reduction of 26% in the aquifer recharge in the last 5 years of serial droughts. In the same period, the elasticity of flow to precipitation was 3.1, which greatly exceeded the long-term value of 2.0. This greater hydrologic sensitivity in the elasticity may represent that the resilience of the surface hydrologic system was transiently lost.

Automated summary

This study focused on the hydroclimate variability in the Jaguari River basin in southeastern Brazil, especially during historical meteorological droughts and the hydrologic response to negative rainfall disturbances. The results indicated that the recent serial meteorological droughts were unprecedented in the last 70 years, resulting in significant hydrologic impacts over a regional scale. The decrease in soil moisture and aquifer recharge, as well as the increased sensitivity in flow to precipitation, suggest a temporary loss of resilience in the surface hydrologic system.