Abstract. Studies on recent climate trends from the Himalayan range are limited, and even completely absent at high elevation (> 5000 m a.s.l.). This study specifically explores the southern slopes of Mt. Everest, analyzing the time series of temperature and precipitation reconstructed from seven stations located between 2660 and 5600 m a.s.l. during 1994–2013, complemented with the data from all existing ground weather stations located on both sides of the mountain range (Koshi Basin) over the same period. Overall we find that the main and most significant increase in temperature is concentrated outside of the monsoon period. Above 5000 m a.s.l. the increasing trend in the time series of minimum temperature (+0.072 °C yr−1) is much stronger than of maximum temperature (+0.009 °C yr−1), while the mean temperature increased by +0.044 °C yr−1. Moreover, we note a substantial liquid precipitation weakening (−9.3 mm yr−1) during the monsoon season. The annual rate of decrease in precipitation at higher elevations is similar to the one at lower elevations on the southern side of the Koshi Basin, but the drier conditions of this remote environment make the fractional loss much more consistent (−47% during the monsoon period). Our results challenge the assumptions on whether temperature or precipitation is the main driver of recent glacier mass changes in the region. The main implications are the following: (1) the negative mass balances of glaciers observed in this region can be more ascribed to a decrease in accumulation (snowfall) than to an increase in surface melting; (2) the melting has only been favoured during winter and spring months and close to the glaciers terminus; (3) a decrease in the probability of snowfall (−10%) has made a significant impact only at glacier ablation zone, but the magnitude of this decrease is distinctly lower than the observed decrease in precipitation; (4) the decrease in accumulation could have caused the observed decrease in glacier flow velocity and the current stagnation of glacier termini, which in turn could have produced more melting under the debris glacier cover, leading to the formation of numerous supraglacial and proglacial lakes that have characterized the region in the last decades.

No abstract

This contribution examines glacier changes on the south side of Mt. Everest from 1962 to 2011 considering five intermediate periods using optical satellite imagery. The investigated glaciers cover ∼ 400 km 2 and present among the largest debris coverage (32 %) and the highest elevations (5720 m) of the world. We found an overall surface area loss of 13.0 ± 3.1 % (median 0.42 ± 0.06 % a −1 ), an upward shift of 182 ± 22 m (3.7 ± 0.5 m a −1 ) in snowline altitude (SLA), a terminus retreat of 403 ± 9 m (median 6.1 ± 0.2 m a −1 ), and an increase of 17.6 ± 3.1 % (median 0.20 ± 0.06 % a −1 ) in debris coverage between 1962 and 2011. The recession process of glaciers has been relentlessly continuous over the past 50 years. Moreover, we observed that (i) glaciers that have increased the debris coverage have experienced a reduced termini retreat (r = 0.87, p < 0.001). Furthermore, more negative mass balances (i.e., upward shift of SLA) induce increases of debris coverage (r = 0.79, p < 0.001); (ii) since early 1990s, we observed a slight but statistically insignificant acceleration of the surface area loss (0.35 ± 0.13 % a −1 in 1962-1992 vs 0.43 ± 0.25 % a −1 in 1992-2011), but an significant upward shift of SLA which increased almost three times (2.2 ± 0.8 m a −1 in 1962-1992 vs 6.1 ± 1.4 m a −1 in 1992-2011). However, the accelerated shrinkage in recent decades (both in terms of surface area loss and SLA shift) has only significantly affected glaciers with the largest sizes (> 10 km 2 ), presenting accumulation zones at higher elevations (r = 0.61, p < 0.001) and along the preferable south-north direction of the monsoons. Moreover, the largest glaciers present median upward shifts of the SLA (220 m) that are nearly double than that of the smallest (119 m); this finding leads to a hypothesis that Mt. Everest glaciers are shrinking, not only due to warming temperatures, but also as a result of weakening Asian monsoons registered over the last few decades. We conclude that the shrinkage of the glaciers in south of Mt. Everest is less than that of others in the western and eastern Himalaya and southern and eastern Tibetan Plateau. Their position in higher elevations have likely reduced the impact of warming on these glaciers, but have not been excluded from a relentlessly continuous and slow recession process over the past 50 years.

Assessment of future water resources under climate change is required in the Himalayas, where hydrological cycle is poorly studied and little understood. This study focuses on the upper Dudh Koshi river of Nepal (151km(2), 4200-8848ma.s.l.) at the toe of Mt. Everest, nesting the debris covered Khumbu, and Khangri Nup glaciers (62km(2)). New data gathered during three years of field campaigns (2012-2014) were used to set up a glacio-hydrological model describing stream flows, snow and ice melt, ice cover thickness and glaciers' flow dynamics. The model was validated, and used to assess changes of the hydrological cycle until 2100. Climate projections are used from three Global Climate Models used in the recent IPCC AR5 under RCP2.6, RCP4.5 and RCP8.5. Flow statistics are estimated for two reference decades 2045-2054, and 2090-2099, and compared against control run CR, 2012-2014. During CR we found a contribution of ice melt to stream flows of 55% yearly, with snow melt contributing for 19%. Future flows are predicted to increase in monsoon season, but to decrease yearly (-4% vs CR on average) at 2045-2054. At the end of century large reduction would occur in all seasons, i.e. -26% vs CR on average at 2090-2099. At half century yearly contribution of ice melt would be on average 45%, and snow melt 28%. At the end of century ice melt would be 31%, and snow contribution 39%. Glaciers in the area are projected to thin largely up to 6500ma.s.l. until 2100, reducing their volume by -50% or more, and their ice covered area by -30% or more. According to our results, in the future water resources in the upper Dudh Koshi would decrease, and depend largely upon snow melt and rainfall, so that adaptation measures to modified water availability will be required.

No abstract

No abstract

No abstract

No abstract