Small mountain lakes, often overlooked as threats, are capable of severe disasters and hence, need constant monitoring, a new study by the Indian Institute of Technology (IIT)-Bhubaneswar has suggested.
Analysing the glacial lake outburst flood (GLOF) in Nepal's Limi Valley in May, it stated that the devastation in Til village was proof that even smaller lakes can trigger a range of immediate and long-term responses. For, the size of the glacial lake does not necessarily control the severity of the outburst.
Located in northwestern Nepal, Til was hit by a sudden debris-laden flood on May 15, sweeping away vital infrastructure including a freshly constructed 15 kW hydropower plant, bridges, roads and nearly 0.25 km² of farmland. The flood destabilised riverbanks, preconditioning further hazards in the valley.
The study 'Flood risk from small mountain lakes', published in Communications Earth & Environment, said the steep and sediment-rich valley sections can transform water flow into a destructive debris-laden flow, greatly increasing the hazard potential. Lateral erosion and slope undercutting during such events can destabilise stream banks, making nearby slopes prone to landslides.
"Infrastructure and assets located tens of meters away and above the stream can be affected during such events. These indirect impacts are often overlooked in typical outburst flood hazard assessments, indicating a gap in current risk evaluation and mitigation," authors of the paper said while arguing that such events are frequently mischaracterised or underestimated in risk assessments, leading to gaps in disaster preparedness.
The study called for recognition and monitoring of risks associated with small lakes in the Himalayas and other high-mountain regions, urging policymakers, scientists, and disaster management agencies to incorporate them in the current approaches to risk assessment.
"The outburst floods from small lakes are not isolated to Nepal. Disastrous consequences of small lake outbursts have recently been reported from other parts including Peruvian Andes. As most of the world’s high mountain regions are witnessing an increase in both the number of glacial lakes and the number of people living downstream, it is critical that potentially underestimated risks such as outburst floods from small lakes are recognised, monitored and addressed," said lead author and assistant professor at IIT Bhubaneswar Ashim Sattar. It is important that these risks are recognised and systematically integrated into existing disaster risk reduction frameworks, he said.
The Himalayas has many small lakes in the higher reaches. However, these conditions and processes are not only localised in High Mountain Asia but other glacierised mountain ranges too, such as the Andes, highlighting the global dimension of this topic, the researchers said.
They also said effective decision-making and sustainable governance need to consider small lakes that can threaten vulnerable downstream communities with limited resilience and coping capacity. "Its high-time for science-based planning, strict policies, early warning systems, and community preparedness, before the next small lake outburst becomes another Himalayan tragedy," opined authors Adam Emmer from Charles University, Prague and Mohd Farooq Azam from International Centre for Integrated Mountain Development (ICIMOD).