Warmed winters and weakened precipitation on Mt. Everest (central southern Himalaya) impacts glaciers, lakes, permafrost, and river discharges

Abstract:

This contribution aims linking temperature and precipitation patterns detected at high elevation of south slopes of Mt. Everest with a) glacier and lake surfaces, b) altitude limit of permafrost, c) frequency of daily river discharges. The study is carried out though:

a) the daily temperature and precipitation reconstruction of the last twenty years (1994-2013) at 5050 m a.s.l. and 25 AWSs located at lower elevation and on Tibetan Plateau

b) glacier surfaces (about 400 km²) and lake areas (more than 100 lakes) since 60s using all available satellite imagery

c) permafrost distribution carried out with soil temperature measurements (2010-2012) compared with previous studies (70s)

d) the results of a stochastic frequency model (wavelet analysis) for detecting river discharge changes in frequency of the Dud Koshi River basin (3000 km²) since 60s.

We observed an increasing temperature trend occurred mainly in winter months, but during the summer ones we observed a slight decreasing of maximum temperature. We confirm for these high elevations the generalized weakening of the monsoon already observed in literature accounting here over 50% of reduction in the last 20 years! In the previous period (70s to 90s) gridded an reanalysis data revealed for our reference site a slighter increase of mean temperature and weak increase of precipitation.

Main climate change driven implications:

- The accelerated shrinkage of glaciers observed in the last twenty years, usually inferred to the temperature increase during the summer months, is ascribed here mainly to the regional monsoon weakening.

- Supraglacial lakes confirm the acceleration of the negative mass balance of glaciers due to reduced ice velocities caused by decreased precipitation.

- Unconnected lakes confirms precisely the observed precipitation trend.

- The altitudinal limit of the permanent permafrost seems to be unchanged since the beginning ‘90s (probably due to stationary summer temperature).

- Rivers discharges experienced in the last ten years an increasing concentrated during the monsoon months. The Wavelet Transform Analysis attributes these increases mainly to a strong reduced accumulation (weaker precipitation) which probably induced lower ice velocities of debris covered tongues and a consequent higher melting.