The response of Hagafellsjökull Vestari glacier, Iceland, to future climate scenarios computed with a dynamic glacier flowline model coupled to a degree-day mass balance model

A dynamic glacier flowline model is coupled to a degree-day mass balance model with the purpose of modelling the response of Hagafellsjökull vestari glacier to future climate change scenarios. The degree-day mass balance model is calibrated using mass balance measurements for the period 1997-2007. The temperature and precipitation input for the calibration is provided by a combination of ERA-40 reanalysis data and local weather station records. The calibrated model shows good agreement with the measured mass balances (r2 = 0.95, RMSE = 0.68 m w.e.). The flowline model is then calibrated against the 2007 surface profile extracted from a DEM constructed from LiDAR data. During calibration the model is run from 1997 to 2007 with the mass balance input provided by the calibrated degree-day model. A number of changes had to be made to the model in order to achieve a good fit with the reference profile. These included a parameterisation of the basal mechanisms of movement (i.e. sliding and deformation of the bed) which was forced by the calculation of water flux at the base; and the introduction of a uniform basal melt rate. The calibrated model calculates the 2007 ice surface profile with an RMSE of 4.41 m. The need to introduce a basal melt rate of 0.8 m yr-1 suggests the presence under the glacier of a significant source of geothermal energy. A range of climate scenarios are imposed on the finalised model to predict the glacier’s behaviour between 2007 and 2109. In the ‘worst-case’ scenario the glacier will lose almost 80% of the 2007 ice volume over the next century. If there is no future climate change relative to the 1978-2007 30-year averages for temperature and precipitation, by 2109 the glacier will lose 30% of the 2007 ice volume and the glacier front will retreat by just over 5 km from its 2007 position