Pre- and post-event Digital Elevation Models (DEMs) and elevation differences for the rock-ice avalanche source area of the August 2026 Trishuli/Rasuwa catastrophic flood

=========================== Introduction On 26 August 2026, a catastrophic debris flow hit the Trishuli river in Nepal and Tibet. We provide here pre-event and post-event Digital Elevation Models (DEMs) of the rock-ice avalanche area from Pléiades, SPOT6 and SPOT5 stereo-images. Date were obtained thanks to the Pléiades World Heritage program of Dinamis (https://dinamis.data-terra.org/) and CNES. The collection includes three files: Rasuwa_mosaic_DEM_pre-event.tif Rasuwa_mosaic_DEM_post-event.tif Rasuwa_mosaic_dh.tif =========================== Methods The post-event DEM is purely based on Pleiades stereo images. The pre-event DEM is based mostly Pléiades and SPOT6 stereopairs. A small fraction of the pre-event DEM was derived from 10 m SPOT5-HRS images. All DEMs were generated at a ground sampling distance of 4 m using the semiglobal matching algorithm of the Ames Stereo Pipeline (Beyer et al., 2018; Shean et al., 2016) and the processing parameters from Deschamps-Berger et al. (2020). A ground sampling distance of 10 m was used for SPOT5-HRS. All individual DEMs were first co-registered and vertically adjusted to the Copernicus 30 (GLO-30) DEM, masking out glaciers using the Randolph Glacier Inventory v7 (RGI 7.0 consortium, 2023). Next, the individual pre- and post-event DEMs were co-registered in pairs to construct the most accurate DoD possible. Finally, those individual DoDs were mosaicked in a single map of elevation difference. The uncertainty on the mean elevation change was calculated using the patch method (Dussaillant et al., 2018). This approach aims to empirically determine the uncertainty associated with the mean elevation change by sampling patches (or tiles) of stable terrain of various sizes to constrain the decay of error with increasing averaging area (Miles et al., 2018; Wagnon et al., 2021). The stable terrain was defined here as excluding glaciers and a buffer around the river channels where erosion or deposition has occurred. For a 1 km² averaging area, the 1-sigma (68th percentile) error and the 2-sigma (95th percentile) error were calculated to be ±0.8 and ±1.8 m, respectively. Beyer, R. A., Alexandrov, O., and McMichael, S.: The Ames Stereo Pipeline: NASA's Open Source Software for Deriving and Processing Terrain Data, Earth and Space Science, 5, 537–548, https://doi.org/10.1029/2018EA000409, 2018. Deschamps-Berger, C., Gascoin, S., Berthier, E., Deems, J., Gutmann, E., Dehecq, A., Shean, D., and Dumont, M.: Snow depth mapping from stereo satellite imagery in mountainous terrain: evaluation using airborne laser-scanning data, The Cryosphere, 14, 2925–2940, https://doi.org/10.5194/tc-14-2925-2020, 2020. Dussaillant, I., Berthier, E., and Brun, F.: Geodetic Mass Balance of the Northern Patagonian Icefield from 2000 to 2012 Using Two Independent Methods, Front. Earth Sci., 6, 8, https://doi.org/10.3389/feart.2018.00008, 2018. Miles, E. S., Watson, C. S., Brun, F., Berthier, E., Esteves, M., Quincey, D. J., Miles, K. E., Hubbard, B., and Wagnon, P.: Glacial and geomorphic effects of a supraglacial lake drainage and outburst event, Everest region, Nepal Himalaya, The Cryosphere, 12, 3891–3905, https://doi.org/10.5194/tc-12-3891-2018, 2018. Nuth, C. and Kääb, A.: Co-registration and bias corrections of satellite elevation data sets for quantifying glacier thickness change, The Cryosphere, 5, 271–290, https://doi.org/10.5194/tc-5-271-2011, 2011. RGI 7.0 Consortium: Randolph Glacier Inventory - A Dataset of Global Glacier Outlines, Version 7.0., 2023. Shean, D. E., Alexandrov, O., Moratto, Z. M., Smith, B. E., Joughin, I. R., Porter, C., and Morin, P.: An automated, open-source pipeline for mass production of digital elevation models (DEMs) from very-high-resolution commercial stereo satellite imagery, ISPRS J. Photogramm., 116, 101–117, https://doi.org/10.1016/j.isprsjprs.2016.03.012, 2016. Wagnon, P., Brun, F., Khadka, A., Berthier, E., Shrestha, D., Vincent, C., Arnaud, Y., Six, D., Dehecq, A., Ménégoz, M., and Jomelli, V.: Reanalysing the 2007–19 glaciological mass-balance series of Mera Glacier, Nepal, Central Himalaya, using geodetic mass balance, Journal of Glaciology, 67, 117–125, https://doi.org/10.1017/jog.2020.88, 2021. =========================== Data Specifications: Cartographic projection: UTM zone 45N (EPSG:32645) Origin of Elevation: meters above WGS84 ellipsoid Raster data format: GeoTIFF NoData value : -9999 This dataset includes only DEMs because a licence needs to be signed with CNES to access Pléiades imagery. =========================== Acknowledgements: Pléiades post-event images were obtained using the CIEST² service developed with CNES by FormaTerre, the solid Earth component of the Data Terra research infrastructure (https://www.poleterresolide.fr/ciest-2-nouvelle-generation-2/). Pléiades and SPOT6 pre-event stereo images were provided through Dinamis (https://dinamis.data-terra.org/) and the Pléiades World Heritage (Pléiades © CNES 2019, distribution AIRBUS DS) SPOT5 images were obtained through the Spot World Heritage (https://regards.cnes.fr/user/swh/) =========================== Dataset Attribution: This dataset is licensed under a Creative Commons CC BY-NC 4.0 International License (Attribution-NonCommercial). =========================== Citation: Please cite this repository as described below: Etienne Berthier. (2026).Pre- and post-event Digital Elevation Models (DEMs) and elevation differences for the rock-ice avalanche source area of the August 2026 Trishuli/Rasuwa catastrophic flood