To support disaster assessment and post‑event research, this dataset comprises pre‑event composite images generated from Copernicus Sentinel‑1 satellite imagery, covering the entire territory of Nepal and the Gyirong County area in Tibet, China. These composites clearly depict the land surface conditions before the disaster (i.e., prior to 26 August 2026). The Sentinel‑1 satellite carries a C‑band Synthetic Aperture Radar (SAR), which provides all‑day and all‑weather imaging capability, unaffected by cloud cover or rain, and offers a spatial resolution of up to 5 metres with a revisit cycle of 6 days. SAR signals are highly sensitive to surface roughness, dielectric constant, and geometric structure, enabling effective identification of subtle surface changes, glacial movements, and river channel morphology prior to the debris flow event, thus making it a valuable data source for disaster monitoring and risk assessment.