Permafrost Collapse in Tibet Triggers Flood in Nepal’s Lhende River

: Permafrost Collapse in Tibet Triggers Flood in Nepal’s Lhende River1

1. Event Summary

• A devastating flood struck Nepal’s Rasuwa district after midnight, traced to a permafrost collapse in the upper catchment of the Lhende River, originating in Tibet.

• The flood destroyed infrastructure, including the Nepal-China friendship bridge at Rasuwagadhi.

2. Scientific Cause

• Permafrost Collapse:

  • Permafrost is permanently frozen terrain (rock, snow, soil) that remains below 0°C year-round.

  • Even minor rainfall or temperature increases can destabilize permafrost, causing sudden floods or landslides.

  • In this event, a section of permafrost collapsed into the river, triggering the flood.

3. Glacial and Hydrological Context

• The Lhende River and its tributaries are fed by multiple glaciers in Tibet and Nepal.

• The region hosts at least seven glacial lakes on the Tibetan side and one in Nepal, making it highly sensitive to melting and collapse events.

4. Role of Climate Change

• Rising Temperatures:

  • Increasing global temperatures and consistent rainfall have been destabilizing permafrost that had remained stable for decades.

  • Warm precipitation and higher temperatures accelerate permafrost melt, sometimes causing underground erosion and surface collapse (thermokarst).

• Precedent Events:

  • Similar permafrost-induced floods have occurred recently, such as in Thame, Solukhumbu, where a glacial lake burst after permafrost melted.

5. Meteorological Observations

• Recent Weather:

  • Only light rainfall was recorded in the 24 hours before the flood, but temperatures at the Kyanjin Glacier Center rose slightly, enough to destabilize permafrost.

  • Satellite data confirmed no significant rainfall or cloud cover at the flood’s origin at the time of the event.

6. Expert and Official Assessments

• Delayed Response:

  • The government’s response was criticized as slow, with warnings about climate risks in the Trans-Himalayan region having gone unheeded.

• Expert Warnings:

  • Geohazard experts noted that even minimal warming or brief showers can trigger major disasters in the Himalayas due to the fragile frozen ground.

7. Wider Implications

• Growing Threat:

  • Nepal’s river systems are increasingly vulnerable to floods originating from glacial and permafrost sources in Tibet.

  • The frequency and severity of such events are rising due to climate change, affecting not only the high mountains but also downstream valleys and plains.

• Changing Rainfall Patterns:

  • The Himalayan region, once shielded from monsoon rains by mountain ridges, is now experiencing increased rainfall and melting, further elevating flood risks.

This categorical breakdown highlights the scientific, climatic, and socio-political dimensions of the permafrost collapse and subsequent flood, emphasizing the urgent need for climate adaptation and disaster preparedness in Himalayan regions1.