The Cryosphere www.the-cryosphere.net 1994-0416 1994-0424 2 2 2008 10.5194/tc-2-191-2008 http://www.the-cryosphere.net/2/191/2008/ http://www.the-cryosphere.net/2/191/2008/tc-2-191-2008.html http://www.the-cryosphere.net/2/191/2008/tc-2-191-2008.pdf 191 204 2008-12-08 Exploring uncertainty in glacier mass balance modelling with Monte Carlo simulation H. Machguth horst.machguth@geo.uzh.ch R. S. Purves J. Oerlemans M. Hoelzle F. Paul Department of Geography, University of Zurich, Zurich, Switzerland Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, The Netherlands By means of Monte Carlo simulations we calculated uncertainty in modelled cumulative mass balance over 400 days at one particular point on the tongue of Morteratsch Glacier, Switzerland, using a glacier energy balance model of intermediate complexity. Before uncertainty assessment, the model was tuned to observed mass balance for the investigated time period and its robustness was tested by comparing observed and modelled mass balance over 11 years, yielding very small deviations. Both systematic and random uncertainties are assigned to twelve input parameters and their respective values estimated from the literature or from available meteorological data sets. The calculated overall uncertainty in the model output is dominated by systematic errors and amounts to 0.7 m w.e. or approximately 10% of total melt over the investigated time span. In order to provide a first order estimate on variability in uncertainty depending on the quality of input data, we conducted a further experiment, calculating overall uncertainty for different levels of uncertainty in measured global radiation and air temperature. 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