Assessment of cloudbursts, extreme rainfall and vulnerable regions in the Upper Ganga basin, Uttarakhand, India

The Upper Ganga Basin (UGB) of Himalayas, located in the state of Uttarakhand, has experienced flash floods caused by extreme rainfall (EREs) and cloudbursts (CBEs). Low predictability of EREs, coupled with insufficient monitoring and inventory of CBEs are limiting factors in the study and identification of Himalayan hazard-prone areas. In this study, 57 EREs/CBEs are compiled and geo-tagged from media reports between 2010 and 2020. These events are authenticated using TRMM/GPM data. The spatial distribution, recurrence and vulnerable areas are analyzed. Cloudbursts occur during the monsoon months of July and August (JA), with approximately 66.6% of events occurring in the elevation band of 1000-2000 m above sea level (m a.s.l.). This elevation band is a potential hazard zone as it is the most populous region in the state. Assessment of rainfall distribution suggests that areas with lower monsoon rainfall have a higher number of EREs/CBEs. This low rainfall valley region also experiences high land surface temperature (LST) in the range of 18 ?-28 ? during JA which could further increase CBEs occurrence highlighting the topography controls. The study identified Joshimath, Bhilangana, Bhatwari, Ukhimath, Dasholi, Deoprayag, Jakholi, Tharali, and Narayanbagad as the most vulnerable blocks and Chamoli, Rudraprayag and Tehri Garhwal as the most vulnerable districts. The assessment showed that about 1 million people spread across 3000 villages in the state are in higher risk regions of EREs/CBEs.

Automated summary

This study analyzes the spatial distribution and vulnerable areas of extreme rainfall and cloudburst events in the Upper Ganga Basin. The study finds that the elevation band of 1000-2000 m above sea level is the most vulnerable, as it is densely populated. Areas with lower monsoon rainfall are more prone to cloudbursts, especially during the months of July and August. The study also identifies the most vulnerable blocks and districts, and estimates that about 1 million people in 3000 villages are at higher risk of extreme rainfall and cloudbursts.