Nepal Flash Flood: Damage Assessment using Sentinel-1 Radar

Completed catalogue assessment

Eligibility decision: Include · Included Resource
Assessment date: 28 September 2026
Decision reason: The original IMPACT/REACH HDX source describes a Sentinel-1 change/damage-screening proxy: 28 August post-event data versus a one-year baseline, a 50 m neighbourhood, a 30 m building buffer and absolute z-score threshold 1.60. It is not proof of structural damage. The source estimates 245.13 ha of high-confidence change within a 4,755 ha built-environment search domain and a 58,557 ha AOI; the two listed original distributions were retrieved.
Metadata corrections: {}

View the complete assessment and exclusion ledger.

Identity and coverage

Catalogue identifier: res-01de4451-c684-5e12-bbae-12624e0e455d
Persistent identifier: 57723eed-8f89-4bec-8ab4-1acd12a34df1
Resource version: HDX metadata state observed 3 September 2026
Publication date: 31 August 2026
Last updated: 3 September 2026
Metadata reviewed: 28 September 2026
Language: English
Geographic coverage: Provider-defined assessment area in the Nepal event corridor, with municipal summaries for the intersecting analysis area.
Bounding box (WGS 84): [84.52739332,27.78286814,85.56596468,28.3460786]
Temporal coverage: 26 August 2025 to 28 August 2026; Mixed
Themes: Damage Proxy, Synthetic Aperture Radar, Buildings, Rapid Prioritization

Method and provenance

Production method: Sentinel-1 IW VV/VH backscatter observations from 26 August 2025 to 26 August 2026 defined a pre-event baseline. The 28 August 2026 acquisition was standardized by z-score; maximum absolute VV/VH anomaly was averaged with a normalized 50 m kernel and restricted to within 30 m of pre-event Overture building footprints. A K50 absolute z-score threshold of at least 1.60 defined the high-confidence layer, which was then visually reviewed and edited.
Provenance: Produced by REACH Initiative/IMPACT Initiatives from Sentinel-1 observations, Overture building footprints, and held-out Copernicus EMSR927 grading data; published through HDX.
Validation: Partially Validated
Uncertainty: Against held-out Copernicus damaged/destroyed observations, the provider reports 53.1% recall and 69.4% F1 for the automated threshold. The zero of 92 'possibly damaged' observations above threshold must not be interpreted as conventional precision or specificity because that class is not verified undamaged.
Limitations: The output is a backscatter-change proxy, not proof of structural damage. Signals can arise from debris, sediment, inundation, moisture, roughness, vegetation, clearance, or other change; damage can also be missed. Steep terrain and viewing geometry are important because dedicated radiometric terrain flattening was not applied.

Access and reuse

Access: Direct Open; open access route
Licence: Creative Commons Attribution (CC BY; version not specified); licence evidence
Redistribution: Permitted Under Stated Package Licence
Catalogue status: Included
Provider page: Open authoritative resource page

Assets

2 assets

Sentinel-1 damage screening by local administrative area — Nepal, version 3

Asset bounding box not stated. Parent resource coverage: Provider-defined assessment area in the Nepal event corridor, with municipal summaries for the intersecting analysis area.

XLSX · 17.7 KiB · Tabular Data · Public Route Or Response Documented

Open access route View details & metadata →

Sentinel-1 high-confidence damage-screening features

WGS 84 bounding box: [84.52739332,27.78738226,85.38748879,28.28104688]

SHP · 52.2 KiB · Archive Or Package · Public Route Or Response Documented