A devastating flash flood tore through Uttarkashi’s Dharali region, with many initially pointing to a cloudburst in the Kheer Ganga river’s upper catchment as the culprit. However, experts are now challenging this narrative, citing insufficient rainfall data to support the cloudburst theory and raising questions about what truly triggered the disaster.
Rohit Thapliyal, a scientist at the India Meteorological Department (IMD), told PTI that the rainfall recorded in Uttarkashi on Tuesday—merely 27 mm—was far too low to classify as a cloudburst. “The data we have does not indicate a cloudburst occurred,” Thapliyal stated.
According to IMD standards, a cloudburst involves rainfall exceeding 100 mm per hour, accompanied by strong winds and lightning, over a small area of 20-30 square kilometers. A 2023 research paper by IIT-Jammu and the National Institute of Hydrology, Roorkee, further defines a cloudburst as a sudden downpour of 100-250 mm per hour over an even smaller area, around one square kilometer. Uttarkashi’s rainfall fell drastically short of these benchmarks.
So, if not a cloudburst, what caused the catastrophic flood? Thapliyal noted that pinpointing the exact cause requires further research. “We can only confirm there was no cloudburst based on meteorological data. The precise trigger is still under investigation,” he said. The mystery has prompted the Uttarakhand Space Application Centre to request satellite imagery from the Indian Space Research Organisation (ISRO) to analyze the event in greater detail.
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D.P. Dobhal, a former scientist at the Wadia Institute of Himalayan Geology, offered an alternative theory. He suggested that the flash flood could have resulted from a different geological event, such as an ice chunk dislodging, a rockfall, or a massive landslide mobilizing moraine deposits in the narrow Kheer Ganga stream. “The area where the sludge came rushing down is in the Alpine region, where cloudbursts are rare due to the altitude,” Dobhal explained. He emphasized that only a thorough analysis of satellite imagery and on-ground data could confirm the true cause.
Uttarakhand’s vulnerability to such disasters is well-documented. A recent study published in the Journal of the Geological Society of India highlighted a significant increase in extreme rainfall and surface runoff events in the state since 2010. Led by Professor Sundriyal, the research noted that while 1998-2009 was marked by warming and reduced rainfall, the post-2010 period saw a surge in intense precipitation, particularly in central and western Uttarakhand. This shift has heightened the region’s susceptibility to flash floods and landslides.
The state’s geology exacerbates these risks. Uttarakhand’s steep slopes, fragile rock formations, and proximity to tectonic faults like the Main Central Thrust make it prone to erosion and instability. The orographic effect of the Himalayas, where moist air is forced upward, often leads to intense, localized rainfall. When combined with unstable slopes, this creates a perfect storm for landslides and flash floods. A November 2023 study in the Natural Hazards journal reported 183 monsoon-related disasters in Uttarakhand between 2020 and 2023, with landslides (34.4%), flash floods (26.5%), and cloudbursts (14%) being the primary culprits.
Human activities have further amplified these natural risks. Experts point to unregulated road construction, deforestation, and the rapid expansion of tourism infrastructure as key contributors. Building settlements and hotels on unstable slopes or riverbanks has significantly increased the region’s exposure to disasters. The Centre for Science and Environment’s Atlas on Weather Disasters revealed that between January 2022 and March 2025, the 13 Himalayan states and Union territories experienced extreme weather events on 822 days, resulting in 2,863 fatalities.
As investigators await satellite imagery and conduct further studies, the Uttarkashi flash flood serves as a stark reminder of the region’s fragility. Whether triggered by a geological event or an underestimated weather phenomenon, the disaster underscores the urgent need for sustainable development practices and robust disaster preparedness in the Himalayas.
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