Provision of detailed continuous long-term hydrological time series data for any river basin is critical for estimation, planning and management of its current and future water resources. Most of the river basins in India are data poor, including its iconic river – Ganga (Ganges). This study assessed the variability of flows under present and ‘naturalized’ basin conditions in the Upper Ganges Basin (UGB) (area of over 87,000 square kilometers (km2)). The naturalized basin conditions are those that existed prior to the development of multiple water regulation structures, and hence may be seen as a reference condition, a starting point, against which to evaluate the impacts of planned basin development, as well as the impacts of future climate change (CC) on basin water resources.