Extensive human-induced modifications of the river corridor, steep terrain and antecedent hydrological conditions significantly intensified the catastrophic flash floods triggered by cloudbursts last year in Himachal Pradesh’s Mandi district, according to the findings of a study.
The findings were reported in the ‘Assessment of 2025 Cloudburst-Induced Flash Flooding in Thunag Village, Mandi, Himachal Pradesh’, based on the research conducted by the Himachal Pradesh University’s Centre for Disaster Risk Reduction and Resilience (CDRRR), officials said.
The research focuses on flash floods that occurred between June 29 and July 1 last year and has been published in Taylor & Francis UK’s ‘Geomatics, Natural Hazards and Risk’ journal.
The assessment was carried out by a team under Mahesh Sharma, Deputy Director of the Centre, during which factors that amplified the disaster beyond the extreme rainfall event were examined.
It observed that while the cloudburst served as the immediate trigger, severity of destruction was largely shaped by local terrain, river dynamics and human interventions within the floodplain.
The team found widespread encroachment of the active floodplain of the rivulet flowing through the village — known as Thunag Khad — through the construction of residential and commercial structures, retaining walls and road embankments. These findings were based on extensive field surveys and supported by high-resolution satellite imagery, officials said.
The study further revealed that structures located immediately adjacent to the river channel suffered the most severe damage, irrespective of their construction type. In contrast, buildings situated only a short distance uphill remained largely unaffected.
Using HEC-RAS rainfall-on-topography simulations, the researchers found that channel constriction and artificial obstructions significantly increased flood depth, flow velocity and the erosive force of floodwaters within the village.
The study concluded that a building’s proximity to hydraulically constrained flow paths was a stronger predictor of damage than its structural characteristics.
Additionally, the research team has developed and validated a satellite-driven hydrodynamic modelling framework for assessing and reducing the impacts of cloudburst-induced flash floods in the Himalayan region, officials added.
