Evolution of Rhonegletscher, Switzerland, over the past 125 years and in the future: application of an improved flowline model

To study the past and future evolution of Rhonegletscher, Switzerland, a flowline model was developed to include valley shape effects more accurately than conventional flowband models. In the model, the ice flux at a gridpoint was computed by a two-dimensional ice-flow model applied to the valley cross-section. The results suggested the underestimation of the accumulation area, which seems to be a general problem of flowline modelling arising from the model’s one-dimensional nature. The corrected mass balance was coupled with the equilibrium-line altitude (ELA) change, which was reconstructed for the period 1878–2003 from temperature and precipitation records, to run the model for the past 125 years. The model satisfactorily reproduced both changes in the terminus position and the total ice volume derived from digital elevation models of the surface obtained by analyses of old maps and aerial photographs. This showed the model’s potential to simulate glacier evolution when an accurate mass balance could be determined. The future evolution of Rhonegletscher was evaluated with three mass-balance conditions: the mean for the period 1994–2003, and the most negative (2003) and positive (1978) mass-balance values for the past 50 years. The model predicted volume changes of –18%, –58% and +38% after 50 years for the three conditions, respectively.