Open Earth Observation for Flash-Flood Vulnerability Diagnosis of an Inaccessible World Heritage City: Shibam, Wadi Hadramawt, Yemen

Armed conflict has closed the Old Walled City of Shibam, a UNESCO World Heritage earthen high-rise city on the List in Danger, to fieldwork, while its flash-flood threat continues, documented from the thirteenth century to the destructive 2008 Hadramawt disaster and Sentinel-1-detected wadi spates in 2025. Openly available Earth observation, therefore, constitutes the only viable diagnostic instrument. This study develops an EO-led flood-vulnerability diagnosis of a 671-hectare study area bounded by the local catchment divide enclosing the city–wadi interface. Cloud-processed multi-temporal Sentinel-2 NDVI composites (Google Earth Engine) characterize the condition of the palm and agricultural buffers that historically moderated runoff; flow accumulation derived from the 30 m Copernicus GLO-30 DEM reconstructs runoff-concentration pathways; and expert visual interpretation of very-high-resolution basemap imagery (Maxar/Airbus via Esri World Imagery) maps land cover, earthen fabric, and urban-edge change — retained deliberately because the spectral similarity of mud-brick fabric to surrounding desert soils defeats automated classification, a documented limitation of global land-cover products over earthen settlements. Layers are classified by explicit criteria and integrated in a hazard–exposure–vulnerability overlay to delineate convergence zones where runoff concentration, weakened ecological buffering, and heritage fragility coincide. In the absence of field validation, the diagnostic geometry is corroborated by triangulation across independent evidence: archival engineering hydrology (2009); independent catchment modeling (2014); multi-source 2008 damage mapping, including DLR rapid satellite assessment; a peer-reviewed regional susceptibility model (2024); and Sentinel-1 flood detections (2025). Outputs comprise a priority-zone classification and spatial decision-support layers for heritage flood-resilience planning, subsequently informing heritage-sensitive landscape strategies. The workflow demonstrates a transferable, reproducible open-EO approach for the world's conflict-affected, data-scarce heritage sites.