Modelling glacier change in the Everest region, Nepal Himalaya

J M Shea,S Bajracharya,P Wagnon,W W Immerzeel,C Vincent

doi:10.5194/tc-9-1105-2015

Abstract

Abstract. In this study, we apply a glacier mass balance and ice redistribution model to examine the sensitivity of glaciers in the Everest region of Nepal to climate change. High-resolution temperature and precipitation fields derived from gridded station data, and bias-corrected with independent station observations, are used to drive the historical model from 1961 to 2007. The model is calibrated against geodetically derived estimates of net glacier mass change from 1992 to 2008, termini position of four large glaciers at the end of the calibration period, average velocities observed on selected debris-covered glaciers, and total glacierized area. We integrate field-based observations of glacier mass balance and ice thickness with remotely sensed observations of decadal glacier change to validate the model. Between 1961 and 2007, the mean modelled volume change over the Dudh Koshi basin is −6.4 ± 1.5 km3, a decrease of 15.6% from the original estimated ice volume in 1961. Modelled glacier area change between 1961 and 2007 is −101.0 ± 11.4 km2, a decrease of approximately 20% from the initial extent. The modelled glacier sensitivity to future climate change is high. Application of temperature and precipitation anomalies from warm/dry and wet/cold end-members of the CMIP5 RCP4.5 and RCP8.5 ensemble results in sustained mass loss from glaciers in the Everest region through the 21st century.

Highlights

High-elevation snow and ice cover play pivotal roles in Himalayan hydrologic systems (e.g. Viviroli et al, 2007; Immerzeel et al, 2010; Racoviteanu et al, 2013)
Calculated γT values are most negative in the premonsoon and least negative during the active phase of the summer monsoon. This is likely a function of the increased moisture advection in the monsoon and pre-monsoon periods, which results in a less negative moist adiabatic lapse rate. These findings are consistent with temperature gradient observations between −0.0046 ◦C m−1 and −0.0064 ◦C m−1 in a nearby Himalayan catchment (Immerzeel et al, 2014b)
At all four Everest-K2-National Research Centre (EVK2CNR) stations, daily temperatures estimated from APHRODITE vertical gradients are greater than observed, with mean daily differences ranging from −1 to +8 ◦C (Fig. 4)

Summary

Introduction

High-elevation snow and ice cover play pivotal roles in Himalayan hydrologic systems (e.g. Viviroli et al, 2007; Immerzeel et al, 2010; Racoviteanu et al, 2013). In the monsoon-affected portions of the Himalayas, meltwater from seasonal snowpacks and glaciers provides an important source of streamflow during pre- and post-monsoon seasons, while rainfall-induced runoff during the monsoon dominates the overall hydrologic cycle (Immerzeel et al, 2013). Against this backdrop, changes in glacier area and volume are expected to have large impacts on the availability of water during the dry seasons (Immerzeel et al, 2010), which will impact agriculture, hydropower generation, and local water resources availability. 110 km, or 25 % of the total glacierized area, is classified as debris-covered (Fig. 2), with surface melt rates that are typically lower than those observed on clean glaciers due to the insulating effect of the debris (Reid and Brock, 2010; Lejeune et al, 2013)

Objectives

Results

Discussion

Conclusion