Modelling drought impacts on the hydrodynamics of a tropical water supply reservoir

Changes in meteorological patterns to drier conditions alter the hydrodynamic processes of reservoirs and can affect their thermal structure. The aim of this study was to assess the impacts of a severe drought period on the hydrodynamics of a tropical reservoir. One-dimensional hydrodynamic modelling was applied from 2009 to 2016 to simulate the thermal dynamics of the highly drought-impacted Serra Azul reservoir, a drinking water supply reservoir located in southeast Brazil. After calibration (r = 0.91, root mean square error [RMSE] = 1.33 degrees C) and validation of the model (r = 0.87, RMSE = 2.06 degrees C), physical indicators were calculated to evaluate the stratification and mixing processes in the water column. Results showed that the reservoir hydrodynamics were affected by the drought period through an increase in mixing frequency and duration. Negative implications for water quality are expected, such as higher concentration of dissolved substances and nutrients and increased turbidity, salinity, and electrical conductivity, as observed in most lakes and reservoirs subjected to drought. Different water withdrawal scenarios were simulated, and a critical water withdrawal volume that could prevent drought impacts on the Serra Azul reservoir thermal regime was identified. This study indicates the need for managers to understand potential impacts of extreme meteorological events in reservoir dynamics, particularly when the reservoirs are part of drinking water systems.