A Geospatial Investigation of the Rishiganga Disaster in Uttarakhand, India

On 7 February 2021, the Chamoli District of Uttarakhand experienced a devastating flood event in the watershed area of Rishiganga and Dhauliganga rivers. The flood was caused by a massive debris flow triggered by a rock avalanche in the Raunthi glaciated valley, resulting in severe destruction in nearby areas and knocking down two major hydropower projects. The detachment of ice, snow, and rock from the slopes of the Trishul mountain range near Raunthi glacier caused a significant impact on the Raunthi Gad valley downstream, destroying the hydropower projects on the way and causing more than 200 deaths. To analyse the changes in the area before and after the rock detachment, we used multi-temporal high-resolution remote sensing imagery, temperature data, seismological data, and digital elevation models (DEM). Our observations suggest that the event was caused by a combination of factors, including the slope gradient, seismic activities, and an increase in temperature from ~−17 to −5 °C from morning to evening of 7 February 2021. Additionally, there was an increase in snow cover from ~149 to 187 km2, which could have contributed to the event. Furthermore, the crack at the point of glacial calving appears to have widened over time due to global temperature variability. We used Sentinel-2 satellite images to estimate the approximate loss in vegetation cover, which was observed to be up to 5 km2. The study also provides a chronological summary of the events that took place on the day of the event, with the help of image analysis and various geospatial and visualization tools. The findings of the study provide valuable insights into the causes of the catastrophic flood event, which can help in developing effective strategies for disaster management and mitigation in the future.