On July 8, a local in Upper Mustang, Nepal, noticed an ominous flood wave rushing down the Chhuhama stream above Chumjung and Lo Manthang, close to the iconic Muktinath temple. The source was a rapidly drained glacial lake high on the Kali Gandaki glacier, located above 5,900 meters altitude.
Over preceding weeks, the lake had steadily grown before emptying itself subglacially over 500 meters. Within hours, the floodwaters had ripped apart four downstream bridges, deposited debris across 35 kilometers, and caused substantial damage.
This was the third highest Glacial Lake Outburst Flood (GLOF) ever recorded in High Mountain Asia, and a harsh reminder of how rapidly the cryosphere is changing under pressure from rising temperatures. At some places this year, temperatures soared 5°C above long-term seasonal averages. Experts say the frequency of GLOFs is increasing — with at least eight reported this year across Nepal, China, Afghanistan, Pakistan, and Kyrgyzstan —triggered by rapid ice melt, permafrost thawing, and newly formed glacial lakes.
Now, all eyes are on NISAR, the joint NASA-ISRO Earth observation satellite launched on July 30, which is being hailed as a game-changer in forecasting such disasters and improving climate resilience.
NISAR mission
The NASA-ISRO Synthetic Aperture Radar (NISAR) mission is the world’s first dual-frequency radar imaging satellite. It combines L-band radar from NASA and S-band radar from ISRO to monitor Earth’s surface changes with unmatched precision — day and night, in all weather conditions.
The first 90 days post-launch are designated for In-Orbit Checkout (IOC), during which systems will be calibrated and tested before full science operations begin. Once operational, NISAR will image the global land and ice-covered surfaces, including islands, sea-ice and selected oceans every 12 days, which experts say is unprecedented.
“NISAR will allow us to detect subtle movements in Earth's surface — including saturated soils on unstable slopes, deformation from earthquakes, and the slow growth of glacial lakes that might not be visible from above,” said Dr Gerald W Bawden, program manager at NASA’s Natural Hazards Research Earth Science Division and a key member of the NISAR launch team, told this newspaper.
Watching the Himalayas
For agencies like the International Centre for Integrated Mountain Development (ICIMOD), which oversees environmental monitoring in the Hindu Kush Himalaya, NISAR represents an invaluable asset.
“While early warning of GLOF will still be complex and challenging, NISAR data will be valuable to study glacier flow and topographic changes for monitoring the glacial environment,” said Birendra Bajracharya, Interim Senior Intervention Manager – Regional Information Service, ICIMOD. “Its ability to penetrate cloud cover will be especially useful to analyse GLOF events, which we increasingly see occurring during the monsoon season.”
Beyond glaciers, NISAR will support assessment of vegetation and wetlands, critical for understanding the broader effects of climate variability. However, Bajracharya cautioned that SAR data does have limitations in complex mountain terrains, a challenge that will extend to NISAR too.
Sudan Bikash Maharjan, remote sensing analyst at ICIMOD, emphasised the importance of slope stability monitoring. “The region is highly vulnerable to unstable slopes due to its fragile terrain and frequent seismic activity. In this context, such data can play a crucial role in developing early alert systems and informed land management planning.”
Dr Jakob Steiner, Fellow at the Himalayan University Consortium, who co-led a working group on risks in the region under the Remote Sensing Environment, Analysis and Climate Technologies Technical Committee (REACT TC), told TNIE: “In many big catastrophic events in the Himalayas, like the floods in Sikkim in 2023, we learned afterwards that many days and sometimes weeks or months before the event, changes were visible in the source area that could have alerted us to a potential disaster in the making. Often this is related to slopes speeding up in their downward movement over time, but can also be water accumulating below the surface. NISAR, with data readily available and its ability to see below the surface, can help us catch these changes before they become a problem. And this would allow us to prepare downstream infrastructure and communities — by, for example, drawing down reservoir storage in hydropower dams (as should have happened in Teesta) or alerting people who live closer to river banks to move away. If caught many months in advance, sometimes even local interventions like draining a slope or lake could be possible,” Steiner said.
The L-Band advantage
According to Tapan Misra, former Director of ISRO’s Space Applications Centre and a radar systems pioneer, NISAR’s inclusion of L-band SAR is especially significant.
“There are only seven active L-band synthetic aperture radar systems globally, and very few provide open-access scientific data. NISAR brings a unique combination of spatial resolution, swath coverage, and revisit frequency that no other L-band mission offers today,” Misra said and this combined with S-band radar from ISRO makes NISAR, a first-of-its-kind satellite in the world.
He explained that L-band SAR, with its longer wavelength (~23.5 cm), can penetrate forest canopies, snow, and even surface layers of dry soil, making it especially suitable for biomass estimation, soil moisture analysis, and detecting subtle ground movement in vegetated and mountainous regions.
“This makes NISAR ideal for monitoring forest degradation, mapping earthquakes and landslides like that of Wayanad disaster in Kerala, and estimating carbon stocks—core areas in both climate science and disaster risk reduction,” Misra noted.
Detecting hazards early
Besides mountains, NISAR’s greatest strength lies in disaster risk reduction on tectonically active and groundwater-stressed lands. “Radar can do what optical imaging cannot — it sees through clouds, operates at night, and even penetrates the Earth’s surface to track movement,” said Dr Bawden. “We can detect whether a slope is saturated with water and likely to fail, or whether tectonic strain is building along a fault line.” This could dramatically change how countries like India, Nepal, and Indonesia monitor seismic zones or respond to floods in real-time.
Organisations like the Coalition for Disaster Resilient Infrastructure (CDRI) are eyeing NISAR to strengthen the safety net for vulnerable nations. “The data from the NASA–ISRO NISAR satellite presents a transformative opportunity to advance CDRI’s mission of strengthening infrastructure resilience against climate and disaster risks, particularly in vulnerable geographies such as Small Island Developing States (SIDS) and Least Developed Countries (LDCs),” Amit Prothi, Director General, CDRI told this newspaper.
He added: “Its global coverage and ability to capture images irrespective of cloud cover or daylight make it particularly valuable for real-time disaster monitoring, resilient recovery planning, and multi-hazard mapping in coastal, mountainous, and drought-prone regions.”
NISAR’s open-data policy, Prothi noted, aligns with CDRI’s vision of embedding risk intelligence into infrastructure design, national adaptation plans, and climate finance strategies.
Forests, water, and land
NISAR will also transform how we monitor forests, wetlands, and groundwater, all of which are directly linked to disaster vulnerability.
By generating the world’s most detailed maps of above-ground woody biomass, NISAR will help scientists better estimate carbon fluxes and detect ecosystem disturbances. In groundwater-stressed regions, the satellite will provide millimeter-precision subsidence maps, offering early warnings of aquifer collapse and urban risk.