Weak precipitation, warm winters and springs impact glaciers of south slopes of Mt. Everest (central Himalaya) in the last 2 decades (1994–2013)

摘要

Studies on recent climate trends from the Himalayan range are limited, andeven completely absent at high elevation (> 5000 m a.s.l.). Thisstudy specifically explores the southern slopes of Mt. Everest, analyzingthe time series of temperature and precipitation reconstructed from sevenstations located between 2660 and 5600 m a.s.l. during 1994–2013,complemented with the data from all existing ground weather stations locatedon both sides of the mountain range (Koshi Basin) over the same period.Overall we find that the main and most significant increase in temperatureis concentrated outside of the monsoon period. Above 5000 m a.s.l. theincreasing 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 liquidprecipitation weakening (?9.3 mm yr?1) during the monsoon season. Theannual rate of decrease in precipitation at higher elevations is similar tothe one at lower elevations on the southern side of the Koshi Basin, but thedrier conditions of this remote environment make the fractional loss muchmore consistent (?47% during the monsoon period). Our results challengethe assumptions on whether temperature or precipitation is the main driverof recent glacier mass changes in the region. The main implications are thefollowing: (1) the negative mass balances of glaciers observed in thisregion can be more ascribed to a decrease in accumulation (snowfall) than toan increase in surface melting; (2) the melting has only been favoured duringwinter and spring months and close to the glaciers terminus; (3) a decreasein the probability of snowfall (?10%) has made a significant impact onlyat glacier ablation zone, but the magnitude of this decrease is distinctlylower than the observed decrease in precipitation; (4) the decrease inaccumulation could have caused the observed decrease in glacier flowvelocity and the current stagnation of glacier termini, which in turn couldhave produced more melting under the debris glacier cover, leading to theformation of numerous supraglacial and proglacial lakes that havecharacterized the region in the last decades.