Characterizing Baseflow in Indian River Basins Using SWOT Discharge Observations

Baseflow is a crucial component of streamflow, essentially driven by changes in groundwater storage, and is vital for sustaining flows during dry periods. Traditional techniques for baseflow quantification using graphical analysis or digital filters require long-term river discharge observations, which are often limited in their spatial extent. However, with the launch of the Surface Water and Ocean Topography (SWOT) mission, global estimates of river discharge are now available over a period of two years, offering a high-resolution dataset with at least one observation every 21 days. Despite its relatively coarse temporal resolution, prior studies have demonstrated SWOT’s ability to accurately estimate average baseflow even at one observation per cycle, based on synthetic SWOT discharge estimates. The high spatial resolution provided by ‘SWOT discharge’ can be utilized to estimate baseflow at a reach-scale and gain new insights into groundwater-surface water interactions in water-stressed river basins.

In this study, we will utilize SWOT’s discharge products over Indian river basins to characterize baseflow dynamics at reach-scale resolution and examine the effects of climate variability and land-use changes on baseflow. By accurately estimating the baseflow recession parameter (k), this study will be able to identify the gaining-to-losing transition in a basin. Furthermore, the research will explore SWOT’s ability to detect temporal shifts in the baseflow recession parameter (k) during the pre-monsoon period and evaluate the effects of anthropogenic extractions on the groundwater table. Finally, these estimates will be integrated into a mass-balance model, baseflow will be converted into upstream groundwater storage (GWS) changes and validated against independent GWS anomalies derived from the Gravity Recovery and Climate Experiment (GRACE) satellites. This study will demonstrate the capability of SWOT to bridge the gap between reach-scale hydraulics and basin-scale storage, providing a vital tool for sustainable water resource management in water-stressed regions.