Seasonal and annual mass balances of Mera and Pokalde glaciers (Nepal Himalaya) since 2007

Abstract

In the Everest region, Nepal, ground-based monitoring programs were started on the debris-free Mera Glacier (27.7° N, 86.9° E; 5.1 km², 6420 to 4940 m a.s.l.) in 2007 and on the small Pokalde Glacier (27.9° N, 86.8° E; 0.1 km², 5690 to 5430 m a.s.l., ∼ 25 km North of Mera Glacier) in 2009. These glaciers lie on the southern flank of the central Himalaya under the direct influence of the Indian monsoon and receive more than 80% of their annual precipitation in summer (June to September). Despite a large inter-annual variability with glacier-wide mass balances ranging from −0.77± 0.40 m w.e. in 2011–2012 (Equilibrium-line altitude (ELA) at ∼ 6055 m a.s.l.) to + 0.46 ± 0.40 m w.e. in 2010–2011 (ELA at ∼ 5340 m a.s.l.), Mera Glacier has been shrinking at a moderate mass balance rate of −0.10± 0.40 m w.e. yr^−1 since 2007. Ice fluxes measured at two distinct transverse cross sections at ∼ 5350 m a.s.l. and ∼ 5520 m a.s.l. confirm that the mean state of this glacier over the last one or two decades corresponds to a limited mass loss, in agreement with remotely-sensed region-wide mass balances of the Everest area. Seasonal mass balance measurements show that ablation and accumulation are concomitant in summer which in turn is the key season controlling the annual glacier-wide mass balance. Unexpectedly, ablation occurs at all elevations in winter due to wind erosion and sublimation, with remobilized snow likely being sublimated in the atmosphere. Between 2009 and 2012, the small Pokalde Glacier lost mass more rapidly than Mera Glacier with respective mean glacier-wide mass balances of −0.72 and −0.26 ± 0.40 m w.e. yr^−1. Low-elevation glaciers, such as Pokalde Glacier, have been usually preferred for in-situ observations in Nepal and more generally in the Himalayas, which may explain why compilations of ground-based mass balances are biased toward negative values compared with the regional mean under the present-day climate

Glacier topography and elevation changes derived from Pléiades sub-meter stereo images

“…These horizontal shifts were obtained (i) by minimising the SD of the elevation differences when two DEMs were compared Rodriguez et al, 2006); (ii) in other cases by estimating the shift between a Pléiades orthoimage and the GNSS measurements acquired along certain trails and roads clearly visible in the images (e.g. Wagnon et al, 2013). When GCPs were used to compute the DEMs, we always verified visually that no horizontal shift of more than one to two pixels (i.e.…”

“…), steep and arid Andes of Argentina to the flat and 7 km wide Astrolabe Glacier, an outlet glacier of the East Antarctic ice sheet in Adélie Land. The main reason for selecting these glaciers was that they were all targets of ongoing field programs Le Meur et al, 2014;Vincent et al, 2009Vincent et al, , 2014Wagnon et al, 2013) so that accurate reference data were available. A Pléiades image is shown for each study site in Fig.…”

Quantifying ice cliff evolution with multi-temporal point clouds on the debris-covered Khumbu Glacier, Nepal

“…The November 2015-May 2016 and May 2016-October 2016 survey intervals are referred to as 'winter' and 'summer', respectively. The Indian summer monsoon spans the months of June to midOctober (Bollasina and others, 2002;Bonasoni and others, 2008) and is when ∼80% of annual precipitation falls (Wagnon and others, 2013).…”

Quantification of different flow components in a high-altitude glacierized catchment (Dudh Koshi, Nepalese Himalaya)

“…Indeed, precipitation is known to be underestimated due to the difficulty of measuring solid precipitation with rain gauges (Wagnon et al, 2013). Precipitation fields provided by different atmospheric models and satellites show also high discrepancies in this region of the Himalayas (Andermann et al, 2011;Palazzi et al, 2013;Ceglar et al, 2017) : another perspective of this study is 30 to test the sensitivity of the model to different precipitation forcing data sets (in-situ, reanalysis, and satellite) and analyze the impact of different precipitation amounts and spatial distributions on the simulated discharges and flow components.…”

“…Only 14% of the basin area is covered by grasslands and shrublands. Glaciers belong to the summer-accumulation type (Wagnon et al, 2013) and are partially fed by avalanches (King et al, 2016;Sherpa et al, 2017). 60% of the glaciers are located between 5000 and 6000 m a.s.l..…”