Storms drenched Nepal’s mountainous Lumbini and Gandaki provinces with waves of torrential rain between September 24 and 27.
The deluge, arriving late in the monsoon season, triggered landslides and pushed the Gandak River, also called the Narayani, to record levels in both Nepal and India.
With runoff streaming into thebraided river system, water overtopped and breached embankments in several areas, inundating farmland and settlements along the river for hundreds of kilometers.
As authorities assessed the full extent of the damage, news reports indicated that flooding andlandslideshad affectedhundreds of villagesand displaced thousands of people.
Images captured byMODIS on NASA’sTerraandAquasatellites on September 20, 2026, and September 29, 2026, show the extent of the flooding.
Thefalse-colorimages combine observations of infrared and visible light to make it easier to distinguish the water.
Floodwater appears blue; vegetation is bright green; clouds are light blue.
In many areas, water inundated seasonal fields on low-lying deposits of sand and silt within the river’s channel, called diara, where flooding is expected.
However, it also breached embankments and flooded several settled areas, including parts ofBagaha, Areraj, and Fulia Khand.
Data from Nepal’s Department of Hydrology and Meteorology indicated that a gauge in Devghāṭ reached as high as11.94 meterson September 27, the highest since measurements began there in the 1960s.
According tonews reports, gauges in India along the Gandak that set new high-water marks included Bagaha, Dumariaghat, Rewaghat, and Lalganj.
NASA has severaltools and datasetsavailable for tracking rainfall and flooding. Among them are Worldview,FLOOD Viewer, and theGPM IMERG Global Viewer.
NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASAEOSDIS LANCEandGIBS/Worldview. Story by Adam Voiland.
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DD IndiaGandak River reaches record 91.25 metres at Bagaha gauge in Bihar. Accessed October 1, 2026.
Dialogue EarthThe silt farmers of the Gandak river. Accessed October 1, 2026.
The HinduDistress and panic in Bihar’s West Champaran district as Gandak river floods. Accessed October 1, 2026.
The Kathmandu PostRelentless rain triggers floods, landslides across Nepal. Accessed October 1, 2026.
The Kathmandu PostIncessant rains trigger widespread flooding in Tarai, disrupt key highway links across Nepal. Accessed October 1, 2026.
National HeraldNarayani river crosses danger level in Nepal, posing risk along Gandak. Accessed October 1, 2026.
Nepal Red CrossMonsoon Update. Accessed October 1, 2026.
News on AirFlood Situation Worsens In North Bihar Due To Continuous Rainfall In Nepal; Over 200 Villages Affected. Accessed October 1, 2026.
Online KhabarNarayani River reaches record water level of 11.94 metres. Accessed October 1, 2026.
The Times of IndiaGandak breaches two more bunds in Saran, Muzaffarpur, IAF joins relief operations. Accessed October 1, 2026.
The PrintGandak sets new flood-level records at four gauge sites in Bihar. Accessed October 1, 2026.
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