Retreat Scenarios of Unteraargletscher, Switzerland, Using a Combined Ice-Flow Mass-Balance Model

Abstract

ABSTRACTThe future evolution of Unteraargletscher, a large valley glacier in the Swiss Alps, is assessed for the period 2005 to 2050 using a flowline model. Detailed measurements of surface velocity from the last decade allow us to relate ice flux to glacier thickness and width. Mass balance is calculated using a distributed temperature-index model calibrated with ice volume changes derived independently from comparison of repeated digital elevation models. The model was validated for the period 1961 to 2005 and showed good agreement between the simulated and observed evolution of surface geometry. Regional climate scenarios with seasonal resolution were used to investigate the anticipated response of Unteraargletscher to future climate changes. Three mass balance scenarios were defined, corresponding to 2.5%, 50%, and 97.5% quantiles of a statistical analysis of 16 different climate model results. We present a forecast of the future extent of Unteraargletscher in the next five decades and analyze relevant parameters with respect to the past. The model predicts a retreat of the glacier terminus of 800–1025 m by 2035, and of 1250–2300 m by 2050. The debris coverage of the glacier tongue reduces the retreat rate by a factor of three. The thinning rate increased by 50–183% by 2050 depending on the scenario applied, compared to the period 1997 to 2005.