Weak precipitation, warm winters and springs impact glaciers of south slopes of Mt. Everest (central Himalaya) in the last 2 decades (1994–2013 (original) (raw)
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The Cryosphere Discussions, 2014
Studies on recent climate trends from the Himalayan range are limited, and even completely absent at high elevation. This contribution specifically explores the southern slopes of Mt. Everest (central Himalaya), analyzing the minimum, maximum, and mean temperature and precipitation time series reconstructed from seven stations located 5 between 2660 and 5600 m a.s.l. over the last twenty years (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013). We complete this analysis with data from all the existing ground weather stations located on both sides of the mountain range (Koshi Basin) over the same period. Overall we observe that the main and more significant increase in temperature is concentrated outside of the monsoon period. At higher elevations minimum temperature (0.072 ± 0.011 C a 1 , 10 p < 0.001) increased far more than maximum temperature (0.009 ± 0.012 C a 1 , p > 0.1), while mean temperature increased by 0.044 ± 0.008 C a 1 , p < 0.05. Moreover, we note a substantial precipitation weakening (9.3 ± 1.8 mm a 1 , p < 0.01 during the monsoon season). The annual rate of decrease at higher elevation is similar to the one at lower altitudes on the southern side of the Koshi Basin, but here the drier conditions 15 of this remote environment make the fractional loss much more consistent (47 % during the monsoon period). This study contributes to change the perspective on which climatic driver (temperature vs. precipitation) led mainly the glacier responses in the last twenty years. The main implications are the following: (1) the negative mass balances of glaciers observed in this region can be more ascribed to less accumulation 20 due to weaker precipitation than to an increase of melting processes.
2016
The mass balance of the majority of Himalayan glaciers is currently negative, and has been for several decades. Region wide averaging of mass change estimates has masked any catchment or glacier scale 10 variability in glacier recession, thus the role of a number of glaciological processes in glacier wastage remains poorly understood. In this study, we quantify surface lowering and mass loss rates for the ablation areas of 32 glaciers in different catchments across the Everest region, and specifically examine the role of glacial lakes in glacier mass change. We then assess how future ice loss is likely to differ depending on glacier hypsometry. Spatially variable ice loss is observed within and between the Dudh Koshi and Tama Koshi catchments and 15 glaciers that flow onto the Tibetan Plateau. Surface lowering rates on glaciers flowing onto the Tibetan Plateau are 54 % and 19 % greater than those flowing southward into the Dudh Koshi and Tama Koshi catchments, respectively. Surface lowering rates of up to-3.78 ± 0.26 m a-1 occurred on some lacustrine terminating glaciers, although glaciers with small lakes showed rates of lowering comparable with those that terminate on land. We suggest that such a range reflects glacial lakes at different stages of development, and that rates of 20 mass loss are likely to increase as glacial lakes expand and deep water calving begins to occur. Hypsometric data reveal a coincidence of the altitude of maximum surface lowering and the main glacier hypsometry in the Dudh Koshi catchment, thus a large volume of ice is readily available for melt. Should predicted CMIP5 RCP 4.5 scenario warming (0.9-2.3 o C by 2100) occur in the study area, 19-30, 17-50 and 14-37 % increases in the total glacierised area below the Equilibrium Line Altitude will occur in the Dudh Koshi and Tama Koshi 25 catchments, and on the Tibetan Plateau. Comparison of our data with a conceptual model of Himalayan glacier shrinkage confirms the presence of three distinct process regimes, with all glaciers in our sample now in a state of accelerating mass loss and meltwater storage.
AGUFM, 2016
Region-wide averaging of Himalayan glacier mass change has masked any catchment or glacier-scale variability in glacier recession; thus the role of a number of glaciological processes in glacier wastage remains poorly understood. In this study, we quantify mass loss rates over the period 2000-2015 for 32 glaciers across the Everest region and assess how future ice loss is likely to differ depending on glacier hypsometry. The mean mass balance of all 32 glaciers in our sample was −0.52 ± 0.22 m water equivalent (w.e.) a −1. The mean mass balance of nine lacustrineterminating glaciers (−0.70 ± 0.26 m w.e. a −1) was 32 % more negative than land-terminating, debris-covered glaciers (−0.53 ± 0.21 m w.e. a −1). The mass balance of lacustrineterminating glaciers is highly variable (−0.45 ± 0.13 to −0.91 ± 0.22 m w.e. a −1), perhaps reflecting glacial lakes at different stages of development. To assess the importance of hypsometry on glacier response to future temperature increases, we calculated current (Dudh Koshi-0.41, Tama Koshi-0.43, Pumqu-0.37) and prospective future glacier accumulation area Ratios (AARs). IPCC AR5 RCP 4.5 warming (0.9-2.3 • C by 2100) could reduce AARs to 0.29 or 0.08 in the Tama Koshi catchment, 0.27 or 0.17 in the Dudh Koshi catchment and 0.29 or 0.18 in the Pumqu catchment. Our results suggest that glacial lake expansion across the Himalayas could expedite ice mass loss and the prediction of future contributions of glacial meltwater to river flow will be complicated by spatially variable glacier responses to climate change. Recent studies have identified spatial heterogeneity in mass loss across the Himalayas in the first decade of the 21st century (
In areas of high relief, many glaciers have extensive covers of supraglacial debris in their ablation zones, which alters both rates and spatial patterns of melting, with important consequences for glacier response to climate change. Wastage of debris-covered glaciers can be associated with the formation of large moraine-dammed lakes, posing risk of glacier lake outburst floods (GLOFs). In this paper, we use observations of glaciers in the Mount Everest region to present an integrated view of debris-covered glacier response to climate change, which helps provide a long-term perspective on evolving GLOF risks. In recent decades, debris-covered glaciers in the Everest region have been losing mass at a mean rate of 0.32 m yr¹, although in most cases there has been little or no change in terminus position. Mass loss occurs by 4 main processes: (1) melting of clean ice close to glacier ELAs; (2) melting beneath surface debris; (3) melting of ice cliffs and calving around the margins of supraglacial ponds; and (4) calving into deep proglacial lakes. Modelling of processes (1) and (2) shows that Everest-region glaciers typically have an inverted ablation gradient in their lower reaches, due to the effects of a down-glacier increase in debris thickness. Mass loss is therefore focused in the mid parts of glacier ablation zones, causing localised surface lowering and a reduction in downglacier surface gradient, which in turn reduce driving stress and glacier velocity, so the lower ablation zones of many glaciers are now stagnant. Model results also indicate that increased summer temperatures have raised the altitude of the rain-snow transition during the summer monsoon period, reducing snow accumulation and ice flux to lower elevations. As downwasting proceeds, formerly efficient supraglacial and englacial drainage networks are broken up, and supraglacial lakes form in hollows on the glacier surface. Ablation rates around supraglacial lakes are typically one or two orders of magnitude greater than sub-debris melt rates, so extensive lake formation accelerates overall rates of ice loss. Most supraglacial lakes are 'perched' above hydrological base level, and are susceptible to drainage if they become connected to the englacial drainage system. Speleological surveys of conduits show that large englacial voids can be created by drainage of warm lake waters along pre-existing weaknesses in the ice. Roof collapses can open these voids up to the surface, and commonly provide the nuclei of new lakes. Thus, by influencing both lake drainage and formation, englacial conduits exert a strong control on surface ablation rates. An important threshold is crossed when downwasting glacier surfaces intersect the hydrological base level of the glacier. Base-level lakes formed behind intact moraine dams can grow monotonically, and in some cases can pose serious GLOF hazards. Glacier termini can evolve in different ways in response to the same climatic forcing, so that potentially hazardous lakes will form in some situations but not others. Additionally, the probability of a flood is not simply a function of lake volume, but depends on the geometry and structure of the dam, and possible trigger mechanisms such as ice-or rockfalls into the lake. Satellite-based measurements of glacier surface gradient and ice velocities allow probable future locations of base-level lakes to be identified. A base-level lake has begun to grow rapidly on Ngozumpa Glacier west of Mount Everest, and could attain a volume of 10 m³ within the next 2 or 3 decades. Unless mitigation efforts are undertaken, this lake could pose considerable GLOF hazard potential.
The volume change of the Chhota Shigri Glacier (India, 32 20 N, 77 300 E) between 1988 and 2010 has been determined using in situ geodetic measurements. This glacier has experienced only a slight mass loss between 1988 and 2010 (–3.8±2.0mw.e. (water equivalent) corresponding to –0.17 pm 0.09mw.e. yr−1). Using satellite digital elevation models (DEM) differencing and field measurements, we measure a negative mass balance (MB) between 1999 and 2010 (–4.8±1.8mw.e. corresponding to –0.44±0.16mw.e. yr−1). Thus, we deduce a slightly positive or near-zero MB between 1988 and 1999 (+1.0±2.7mw.e. corresponding to +0.09±0.24mw.e. yr−1). Furthermore, satellite DEM differencing reveals that the MB of the Chhota Shigri Glacier (–0.39 pm 0.15mw.e. yr−1) has been only slightly less negative than the MB of a 2110 km2 glaciarized area in the Lahaul and Spiti region (–0.44±0.09mw.e. yr−1) during 1999–2011. Hence, we conclude that the ice wastage is probably moderate in this region over the last 22 yr, with near equilibrium conditions during the nineties, and an ice mass loss after. The turning point from balanced to negative mass budget is not known but lies probably in the late nineties and at the latest in 1999. This positive or near-zero MB for Chhota Shigri Glacier (and probably for the surrounding glaciers of the Lahaul and Spiti region) during at least part of the 1990s contrasts with a recent compilation of MB data in the Himalayan range that indicated ice wastage since 1975. However, in agreement with this compilation, we confirm more negative balances since the beginning of the 21st century.
Quaternary International, 2021
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We use remote-sensing and GIS technologies to monitor glacier changes in the Koshi River basin, central Himalaya. The results indicate that in 2009 there were 2061 glaciers in this region, with a total area of 3225 AE 90.3 km 2 . This glacier population is divided into 1290 glaciers, with a total area of 1961 AE 54.9 km 2 , on the north side of the Himalaya (NSH), and 771 glaciers, with a total area of 1264 AE 35.4 km 2 , on the south side of the Himalaya (SSH). From 1976 to 2009, glacier area in the basin decreased by about 19 AE 5.6% (0.59 AE 0.17% a -1 ). Glacier reduction was slightly faster on SSH (20.3 AE 5.6%) than on NSH (18.8 AE 5.6%). The maximum contribution to glacier area loss came from glaciers within the 1-5 km 2 area interval, which accounted for 32% of total area loss between 1976 and 2009. The number of glaciers in the Koshi River catchment decreased by 145 between 1976 and 2009.
The Cryosphere, 2017
Region-wide averaging of Himalayan glacier mass change has masked any catchment or glacier-scale variability in glacier recession; thus the role of a number of glaciological processes in glacier wastage remains poorly understood. In this study, we quantify mass loss rates over the period 2000-2015 for 32 glaciers across the Everest region and assess how future ice loss is likely to differ depending on glacier hypsometry. The mean mass balance of all 32 glaciers in our sample was −0.52 ± 0.22 m water equivalent (w.e.) a −1. The mean mass balance of nine lacustrineterminating glaciers (−0.70 ± 0.26 m w.e. a −1) was 32 % more negative than land-terminating, debris-covered glaciers (−0.53 ± 0.21 m w.e. a −1). The mass balance of lacustrineterminating glaciers is highly variable (−0.45 ± 0.13 to −0.91 ± 0.22 m w.e. a −1), perhaps reflecting glacial lakes at different stages of development. To assess the importance of hypsometry on glacier response to future temperature increases, we calculated current (Dudh Koshi-0.41, Tama Koshi-0.43, Pumqu-0.37) and prospective future glacier accumulation area Ratios (AARs). IPCC AR5 RCP 4.5 warming (0.9-2.3 • C by 2100) could reduce AARs to 0.29 or 0.08 in the Tama Koshi catchment, 0.27 or 0.17 in the Dudh Koshi catchment and 0.29 or 0.18 in the Pumqu catchment. Our results suggest that glacial lake expansion across the Himalayas could expedite ice mass loss and the prediction of future contributions of glacial meltwater to river flow will be complicated by spatially variable glacier responses to climate change. Recent studies have identified spatial heterogeneity in mass loss across the Himalayas in the first decade of the 21st century (
Observed changes in Himalayan glaciers
Current Science, 2014
In the Himalaya, large areas are covere d by glaciers and seasonal snow. They are an important source of water for the Himalayan rivers. In this article, observe d changes in glacial extent and mass balance have been discussed. Various studies suggest that most of the Himalayan glaciers are retreating though the rate of retreat varies from glacier to glacier, ranging from a few meters to almost 61 m/year, de pe nding upon the terrain and meteorological parameters. In addition, mapping of almost 11,000 out of 40,000 sq. km of glaciate d area, distribute d in all major climatic zones of the Himalaya, suggests an almost 13% loss in area in the last 4-5 decades. The glacier mass balance observations and estimates made using methods like field, AAR, ELA and geodetic me asure me nts, suggest a significant increase in mass wastage of Himalayan glacie rs in the last 3-4 decades. In the last four decades loss in glacial ice has been estimated at 19 7 m. This suggests loss of 443 136 Gt of glacial mass out of a total 3600-4400 Gt of glacial store d water in the Indian Himalaya. This study has also shown that mean loss in glacier mass in the Indian Himalaya is accelerate d from -9 4 to -20 4 Gt/year between the periods 1975-85 and 2000-2010. The estimate of glacial stored water in the Indian Himalaya is base d on glacier inve ntory on a 1 : 250,000 scale and scaling methods; the refore, we assume uncertainties to be large.