Abstract
Abstract. In the Everest region, Nepal, ground-based monitoring programmes 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 −0.67 ± 0.28 m w.e. in 2011–2012 (Equilibrium-line altitude (ELA) at ~ 5800 m a.s.l.) to +0.46 ± 0.28 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 −0.08 ± 0.28 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 remobilised snow potentially 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 −0.23 ± 0.28 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.
Highlights
Since the erroneous statement in the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report that Himalayan glaciers could disappear in the coming decades if the Earth keeps warming at the current rate (Cogley et al, 2010), these glaciers have drawn the attention of a growing number of scientists (e.g. Bolch et al, 2012; Kääb et al, 2012)
On Mera Glacier the equilibrium-line altitude (ELA) varied from a minimum of 5335 m a.s.l. in 2010–2011 (Ba = 0.46 ± 0.28 m w.e.; AAR = 0.89) to a maximum of 5800 m a.s.l. in 2011–2012 (Ba = −0.67 ± 0.28 m w.e.; AAR = 0.29)
Seasonal mass balance measurements on Mera and Pokalde glaciers confirm that ablation and accumulation are concomitant in summer which in turn is the key season controlling the annual glacier mass balance (Figs. 6–7)
Summary
Since the erroneous statement in the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report that Himalayan glaciers could disappear in the coming decades if the Earth keeps warming at the current rate (Cogley et al, 2010), these glaciers have drawn the attention of a growing number of scientists (e.g. Bolch et al, 2012; Kääb et al, 2012). Karakoram-Himalayan glaciers cover the largest glacierized area on Earth outside the polar regions (∼ 40 800 km2; Bolch et al, 2012) They experience contrasting precipitation regimes, with a decreasing influence of the westerlies from west to east, and a simultaneous increasing influence of the Indian and Asian monsoons, allowing two striking gradients to emerge: an east-to-west rainfall gradient along the Himalayan foreland, and a south-to-north gradient across the Himalayan range due to topography and relief (Burbank et al, 2003; Bookhagen and Burbank, 2006, 2010). Groundbased observations everywhere along the entire range are not possible, but in-situ measurements are needed to confirm remotely-sensed observations and quantify important variables not measurable from space such as annual and seasonal mass balances, mass balance gradients and snow/ice melt factors for degree-day models
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