Study region: Upper Cauvery river basin, India Study focus: Reservoir construction is one of the major contributors to changes in natural river flow regime characteristics. This study aims to understand the hydrological alterations resulting from the construction of reservoirs and water abstraction in the upper regions of the basin. The impacts of dams on river flow regimes where data is available only for periods after the construction of the dams is assessed. A landscape-based hydrological model, FLEX-Topo, is used to model the flows contributed by the upstream and downstream areas of four major reservoirs in the study area. A separate reservoir operation model is developed for each of the reservoirs. Next, the hydrological model is integrated with the reservoir model and the modelled flow at the downstream streamflow gauging station of each of the corresponding four sub-basins is calibrated. The modelled flow regimes with and without reservoirs are then compared using the indicators of hydrological alterations to understand the degree to which the flows have been altered by the reservoirs. New hydrological insights for the region: The results indicate that flow regimes have been modified from their natural state following reservoir impoundment and water abstractions. Significant impacts are observed in median monthly flow, 1-day minimum flow and low pulses. Such information could provide a reference to water managers to replicate the natural flow regimes, help sustain natural biota and thus contribute toward the sustainable management of river basins in India.