Glacier Lake Outburst Floods of Uttarakhand: A Case Study on Dharali Flash Flood Disaster 2025

Abstract

Uttarakhand, located in the Himalayas, is a globally recognised biodiversity-rich mountain ecosystem. It has fragile geology, steep slopes, and a dense network of glacial rivers, including the Ganga and Yamuna. Over the past three decades, the state has faced several disasters, including the 2013 Kedarnath tragedy, the 2021 Chamoli avalanche, and the 2025 Dharali flash flood, which were the most devastating. The present study focused on the Dharali flash flood in Naugaon block of Uttarkashi district, located at 30.90°N, 78.68°E on the banks of the Bhagirathi River. Their population, according to the 2011 census, was 583. The economy is largely based on farming, apple orchards, and tourism centred on Gangotri. Local reports indicate repeated flooding in 2010, 2012, and 2018. This study investigates on the rainfall, glacial lake outburst floods (GLOFs) originated flash flood analysis, and examines underlying causes and consequences of the Dharali disaster, On the 5 August 2025 between 1:30 and 2:00 PM, in the Kheer Ganga River- a tributary of the Bhagirathi experience a flash flood, that resulted widened stream and deposited a fan-shaped spread of sediment and debris (~20 hectares ; (~750 m × ~450 m) at the river confluence and the satellite assessment, lending to the destruction of 130 houses, hotels, historic kalp-kedar temple and many more structures submerged and swept away. Although the event was initially misclassified as a cloudburst, subsequent analyses by ISRO and IMD confirmed that it was primarily triggered by GLOFs, with extreme rainfall as a secondary factor. The Dharali flood demonstrates the dangerous intersection of deforestation, unplanned development, artificially altered river pathways, and climate change, which enhances the disaster's impact. The study's findings emphasise the urgent need for continuous glacier monitoring, satellite-based early warning systems, land-use planning with strict regulation of riverside development, and stronger governance interventions to curb unplanned growth in these areas.