Understanding the flash flood event of 7th February 2021 in Rishi Ganga basin, Central Himalaya using remote sensing technique

Abstract

On 7th February 2021, a sudden flash flood in the Rishi and Dhauli Ganga rivers in Uttarakhand Himalaya killed 80 people and left 124 people missing. Two hydropower projects were completely destroyed. The flash flood was caused by an avalanche and debris flow. In the present study, spatio-temporal variation in dynamics of glaciers and meteorological parameters including precipitation, land surface temperature etc. was investigated. The study also indicates tectonic correlation with high velocity in the region. A significant change in the climatic conditions just before the flashflood event was observed. Snow cover trend indicates heavy snowfall precipitation followed by abrupt escalation in the difference between diurnal temperatures in the Tapovan valley. Our findings suggest that a sudden temperature change couple of days before caused rapid glacier melt. The melt water moved down along the pre-existing joint/fracture plane, causing the wedge to fail and a flash flood to occur. It is envisioned that the recent change in weather conditions in the region is the primary cause of this event. The steep, narrow river valley increases the kinetic energy of the river, causing even more devastation in its lower reaches. Due to climate change, the Himalayan glaciers have melted rapidly over the last century, expanding the size of glacier lakes and depositing massive sediments in de-glaciated areas. Based on the recent flash flood event and the previous Kedarnath tragedy, it is critical to monitor such potential glacier areas in order to avoid such unfortunate hazards in the future.