The distribution and hydrological significance of rock glaciers in the Nepalese Himalaya

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.In the Nepalese Himalaya, there is little information on the number, spatial distribution and morphometric characteristics of rock glaciers, and this information is required if their hydrological contribution is to be understood. Based on freely available fine spatial resolution satellite data accessible through Google Earth, we produced the first comprehensive Nepalese rock glacier inventory, supported through statistical validation and field survey. The inventory includes the location of over 6000 rock glaciers, with a mean specific density of 3.4%. This corresponds to an areal coverage of 1371 km². Our approach subsampled approximately 20% of the total identified rock glacier inventory (n = 1137) and digitised their outlines so that quantitative/qualitative landform attributes could be extracted. Intact landforms (containing ice) accounted for 68% of the subsample, and the remaining were classified as relict (not containing ice). The majority (56%) were found to have a northerly aspect (NE, N, and NW), and landforms situated within north- to west-aspects reside at lower elevations than those with south- to- east aspects. In Nepal, we show that rock glaciers are situated between 3225 to 5675 m a.s.l., with the mean minimum elevation at the front estimated to be 4977±280 m a.s.l. for intact landforms and 4541±346 m a.s.l. for relict landforms. The hydrological significance of rock glaciers in Nepal was then established by statistically upscaling the results from the subsample to estimate that these cryospheric reserves store between 16.72 and 25.08 billion cubic metres of water. This study, for the first time, estimates rock glacier water volume equivalents and evaluates their relative hydrological importance in comparison to ice glaciers. Across the Nepalese Himalaya, rock glacier to ice glacier water volume equivalent is 1:9, and generally increases westwards (e.g., ratio = 1:3, West region). This inventory represents a preliminary step for understanding the spatial distribution and the geomorphic conditions necessary for rock glacier formation in the Himalaya. With continued climatically-driven ice glacier recession, the relative importance of rock glaciers in the Nepalese Himalaya will potentially increase.This work was supported by the Natural Environment Research Council (grant number: 851 NE/L002434/1 to DBJ); the Royal Geographical Society (with IBG) with a Dudley Stamp Memorial Award 852 (awarded to DBJ); the European Union Seventh Framework Programme FP7/2007-2013 (grant number: 603864 853 to SH and RAB [HELIX: High-End cLimate Impacts and eXtremes; www.helixclimate.eu]). The work of RB forms 854 part of the BEIS/Defra Met Office Hadley Centre Climate Programme GA01101.