Modelled climate sensitivity of the mass balance of Morteratschgletscher and its dependence on albedo parameterization

Abstract

This paper presents a study of the climate sensitivity of the mass balance of Morteratschgletscher in Switzerland, estimated from a two-dimensional mass balance model. Since the albedo scheme chosen is often the largest error source in mass balance models, we investigated the impact of using different albedo parameterizations on the climate sensitivity of the mass balance. We first ran the mass balance model for the period 1980 to 2002 and calculated the mass balance sensitivity by perturbing the air temperature by values ranging from −2 to +2 K and precipsitation by values ranging from −20 to +20%. The albedo parameterization that we used for these simulations relates the snow albedo to snow age and snow depth, whereas it considers the ice albedo constant in time and space. The mass balance sensitivity to temperature and precipitation was estimated at −59 cmWE year−1 K−1 and at 17 cmWE year−1 per 10% respectively (cmWE: centimetres water equivalent). Then, we used three other albedo parameterizations. One parameterization uses ice albedo values that vary in space and were acquired from a Landsat image. Another parameterization calculates the snow albedo from accumulated daily maximum temperatures since snowfall. The third parameterization is the simplest and uses two constant albedo values, one for snow and one for ice. The differences between sensitivities calculated from the different albedo parameterizations were generally small. However, when the simplest parameterization was used, the mass balance sensitivity to temperature decreased to −52 cmWE year−1 K−1. This is mainly due to the constant snow albedo, which implies that the albedo feedback is not fully considered. For an accurate estimate of the mass balance sensitivity, the albedo parameterization should capture the process of a decreasing snow albedo when a snow pack gets older or thinner.