Estimation of Ecological Flow for Major Indian River Basins under Changing Climate

Streamflow provides critical support for the biodiversity of aquatic and riparian ecosystems, sediment transport, and nutrient cycling. Therefore, a minimum streamflow in rivers is crucial for sustaining the proper functioning of aquatic habitats. However, lean or low-flow regimes have been significantly altered by various human activities, such as dam construction, flow diversion for irrigation purposes, industrialisation, and urbanisation. Moreover, changing climate is causing erratic monsoons, increased temperatures, and more prolonged droughts, thereby maintaining ecological flow has become increasingly challenging and urgent to preserve the riverine ecosystems. Our aim is to develop a robust, data-driven framework for estimating environmental flows (E-flows) across 55 stations in major Indian river basins. The primary objective is to assess the quantity and timing of streamflow required to sustain the various river ecosystems, utilising hydrological indicators and long-term datasets, such as temperature and precipitation from the Indian Meteorological Department (IMD). Changes in streamflow characteristics are assessed by comparing observed and machine learning-based naturalised flows, enabling the isolation of reservoir-induced impacts on the streamflow regime, magnitude, duration, and seasonal timing. The study hypothesises that, with the use of observed streamflow data, naturalised streamflow reconstruction and a multi-indicator hydrologic approach, integrating Indicators of Hydrological Alteration (IHA), the Range of Variability Approach (RVA), and Flow Duration Curve (FDC) analysis, can provide reliable E-Flow estimates at regional and national scales. By comparing indicator-based benchmarks derived from observed and naturalised streamflow, the stations are classified according to the degree of hydrologic alteration, thereby supporting scientifically informed river management and policy decisions.