Alpine-wide distributed glacier mass balance modelling: a tool for assessing future glacier change?

Abstract

Distributed glacier mass balance models enable the calculation of the mass balance for each point of a glacier surface from meteorological input data. In view of the observed enhanced down-wasting of Alpine glaciers in recent years, such models become increasingly valuable for assessment of ongoing and future glacier change. However, their potential for large-area application by using gridded input data sets has not been fully exploited yet. In this contribution we describe the major components of distributed glacier mass balance models and apply a model that is based on the calculation of the energy balance to a larger test site (Mischabel region) in Switzerland.We thereby force the model with gridded data sets from annual precipitation, satellite-derived albedo and daily potential solar radiation as well as climatic means of meteorological variables. While the latter can easily be tuned to agree with observed mass balance distributions of specific glaciers, other nearby glaciers get unrealistically high positive or negative balances in the same simulation. Besides a variable sensitivity of individual glaciers, this hints to processes acting on a local scale, that are not yet considered in the model (e.g. snow redistribution by wind). However, the model is well suited for sensitivity studies with the included variables, and the mass balance sensitivities obtained agree well with results from previous studies (e.g. we calculate a 125 m rise of the equilibrium line altitude (ELA) for a 1 °C temperature increase). Once the local processes have been included successfully, we see a large potential of forcing such models with future climate data as computed by regional climate models. The resulting changes in mass balance or ELA on a glacier-specific basis may then be used as an input for further impact models which calculate future discharge or water resources.