# UAV-Derived Himalayan Topography: Hazard Assessments and Comparison with Global DEM Products
## 5 Conclusions  
We have shown the value of fine-resolution UAV-derived DEMs and orthophotos for topographic representation and hazard assessment in the high mountain Himalaya. UAV DEMs acquired for monitoring purposes or in response to a disaster can be compared against the existing topography to quantify surface elevation change or be used for real-time decision making, such as deriving landslide-dammed lake volumes and socioeconomic vulnerabilities. Where available, 8 m High Mountain Asia DEMs offer a clear improvement over existing global DEM products, such as the GDEM2, AW3D30, and SRTM, and will form an important baseline topographic dataset. Of the global DEM products, the GDEM2 consistently had the highest vertical difference compared to fine-resolution UAV-derived DEMs in our areas of interest, whereas the AW3D30 and SRTM DEMs had comparable and improved topographic representation. We showed that landslide-dammed lakes occurring on the Marsyangdi River following the 2015 Gorkha earthquake would not have posed an inundation hazard to Lower Pisang village during a sudden breach scenario. Fine-resolution DEMs were not available at the time of the event, but subsequent availability of HMA DEMs allowed the calculation of landslide volume and produced simulated landslide-dammed lake area and volumes similar to the UAV-derived DEM. Therefore, continued acquisition of fine-resolution topography is high priority in Nepal, where landslide and flood hazards are common. The UAV-derived data (available on request to the corresponding author) should be used to inform assessments of future hazards and socio-economic vulnerabilities along the Marsyangdi River.  
The following are available online at [[http://www.mdpi.com/2504-446X/3/1/18/s1](http://www.mdpi.com/2504-446X/3/1/18/s1)]([http://www.mdpi.com/2504-446X/3/1/18/s1](http://www.mdpi.com/2504-446X/3/1/18/s1)), Table S1: Coregistration of open access and the UAV DEMs. Figure S1. **(a,b)** Photographs of landslides and rockfall adjacent to Tal village. Photographs taken in October 2013 by [PERSON]. **(c)** Photograph of the river-blocking landslide on the Marsyangdi River. Photograph taken in April 2018 by [PERSON].  
Conceptualisation, methodology, formal analysis C.S.W.; writing--original draft preparation, C.S.W.; writing--review and editing, C.S.W., J.S.K. and B.T. visualisation, C.S.W.; funding acquisition, J.S.K.  
The Civil Aviation Authority of Nepal and Home Ministry of Nepal are thanked for providing a UAV permit. We thank the Nepal Department of National Parks and Wildlife Conservation, and the Himalayan Research Centre for facilitating a research permit for this work. We thank Planet Labs for providing access to satellite imagery through the Planet Ambassadors Program. ASTER GDEM is a product of NASA and METI. The AW3D30 DEM is provided by the Japan Aerospace Exploration Agency (JAXA) at [[http://www.eorc.jaxa.jp/ALOS/en/aw3d30/](http://www.eorc.jaxa.jp/ALOS/en/aw3d30/)]([http://www.eorc.jaxa.jp/ALOS/en/aw3d30/](http://www.eorc.jaxa.jp/ALOS/en/aw3d30/)). High Mountain Asia 8-meter Digital Elevation Models were downloaded from the NASA National Snow and Ice Data Center Distributed Active Archive Center. We thank the two reviewers for their comments, which helped improve this manuscript.  
The authors declare no conflict of interest.