Northern India is home to large river basins, particularly the Ganga and its Himalayan tributaries, transporting a vast amount of water to the Bay of Bengal annually (Sinha & Tandon, 2014). These river basins are also characterized as some of the world's most disastrous flood-prone regions (Sinha et al., 2022;Wasson et al., 2019), producing catastrophic floods annually. Over 18 million people are directly affected by increasing flood frequencies caused by extreme rainfall events each year (Kumar & Mishra, 2020;Rupa & Mujumdar, 2019;Swarnkar et al., 2021). The Himalayas have an extensive glacier cover (Zhang et al., 2015) that contributes meltwater to the Himalayan Rivers (Ganjoo, 2021) during pre-monsoon months (January-May). Lutz et al. (2014) observed that the rainfall contributes to streamflow significantly higher than the snowmelt, glacier melt, and baseflow in the entire Himalayan region. Their estimates also suggest that around 70% of discharge comes from the rainfall in the west-central Himalayan region. The projected increase in snow-melt contribution, however, Anand et al. (2021) will likely intensify the flood risk further.The increasing precipitation intensity in the Himalayan basins is a result of the observable hydrometeorological changes in a warming climate. Consequently, these basins frequently witness increased "flashiness" of storm events (Bookhagen, 2010;Nandargi & Dhar, 2011). For example, the western and west-central Himalayas have experienced a doubling in extreme flows during 1980 -2003(Chug et al., 2020. Several high-magnitude flooding events have been reported in the last decade, such as the 2013 and 2021 floods in Uttarakhand (Allen Abstract The west-central Himalayan River basins face significant damage caused by extreme floods annually. We selected the upper Ganga basin (UGB), the west-central Himalayan basin, to demonstrate how maximum cumulative storm and total rainfall received during monsoon control the extreme flow variability. In addition, the downscaled CMIP6 data sets were used for projections of extremes. The results suggest that historically Alaknanda basin receives a relatively higher magnitude of monsoon and storm rainfall than the other regions in the UGB, which manifested into significant extreme flow variability at the Alaknanda outlet. The extreme flows at the UGB outlet are projected to be more frequent under warming scenarios. The nonstationary flood frequency magnitudes are higher than those obtained from the stationary frequency method, implying a need for a review of return periods used in the designs of flood control structures in the region.Plain Language Summary Floods are frequent natural disasters in India that affect millions of people and disrupt socioeconomic conditions. Climate change and human interventions further exaggerate flood hazards in many regions of the country. The west and west-central Indian Himalayas are the worst flood-affected regions in recent decades. A detailed scientific analysis is, therefore, crucial for sustainable flood management. ...
