Last week’s flash floods, which devastated vast swathes stretching south from the Nepal-Tibet border, have killed more than a thousand people even as thousands of others remain untraced. Two-thirds of a glacier on the Langtang Lirung peak near the border broke off, sending debris plunging vertically into the Lhende stream and causing a colossal wall of water, mud, ice and rocks that ripped through a 90-km stretch down the corridor of Bhotekoshi and Trishuli rivers within an hour or so. Entire settlements along the way were wiped out.
The disaster is a painful lesson on the importance of preparing for catastrophes of such ferocity with the tools in hand. Among other things, a failure to act in time on information from space-based monitoring led to such a massive toll in life, property and ecology.
A fleet of sophisticated ground-observing satellites—including the Nasa-Isro Synthetic Aperture Radar or NISAR and the European Space Agency’s Sentinel-1 constellation—are constantly patrolling along a low-Earth orbit to detect tell-tale early signs of such calamities. NISAR and Sentinel-1, which is run under the European Union’s Copernicus programme for environmental observation, are polar-orbiting, radar-imagery satellites that use synthetic apertures to detect even changes of millimetres on the ground. They relay the data to stations located across the world, particularly for tracking crust deformations, floods, volcanic activities and earthquakes. These satellites can detect small changes on the Earth’s surface even in mountainous regions like the Himalayas.
A recent analysis of data relayed by Sentinel-1, published in Nature, showed that the Langtang Lirung peak glacier was accelerating while moving downhill; the latest observation was taken just seven days before the disaster struck. China’s Institute of Mountain Hazards and Environment, Switzerland’s Asian Mountain Academic Alliance and the US’s Stimson Centre had analysed satellite images to find changes in the glacier and the surrounding terrain that suggested that the system was becoming unstable. And yet, no alarm was sounded—let alone evacuation carried out—to save people in the path of the catastrophe.
While this is a lesson for the world, India in particular needs to sit up and take note considering lakhs of people in the fragile Lower Himalayas and Indo-Gangetic plains face similar threats, and the impact of such destruction could be manifold larger.