title: Adjustment of regional climate model output for modeling the climatic mass balance of all glaciers on Svalbard.
abstract: Large-scale modeling of glacier mass balance relies often on the output from regional climate models (RCMs). However, the limited accuracy and spatial resolution of RCM output pose limitations on mass balance simulations at subregional or local scales. Moreover, RCM output is still rarely available over larger regions or for longer time periods. This study evaluates the extent to which it is possible to derive reliable region-wide glacier mass balance estimates, using coarse resolution (10 km) RCM output for model forcing. Our data cover the entire Svalbard archipelago over one decade. To calculate mass balance, we use an index-based model. Model parameters are not calibrated, but the RCM air temperature and precipitation fields are adjusted using in situ mass balance measurements as reference. We compare two different calibration methods: root mean square error minimization and regression optimization. The obtained air temperature shifts (+1.43°C versus +2.22°C) and precipitation scaling factors (1.23 versus 1.86) differ considerably between the two methods, which we attribute to inhomogeneities in the spatiotemporal distribution of the reference data. Our modeling suggests a mean annual climatic mass balance of -0.05 ± 0.40 m w.e. a-1for Svalbard over 2000-2011 and a mean equilibrium line altitude of 452 ± 200 m  above sea level. We find that the limited spatial resolution of the RCM forcing with respect to real surface topography and the usage of spatially homogeneous RCM output adjustments and mass balance model parameters are responsible for much of the modeling uncertainty. Sensitivity of the results to model parameter uncertainty is comparably small and of minor importance.
authors.affiliation: Department of Geography RWTH Aachen University Aachen Germany; Institute of Atmospheric and Cryospheric Sciences University of Innsbruck Innsbruck Austria.
authors.forename: Marco
authors.initials: M
authors.lastname: Möller
authors.affiliation: Institute of Atmospheric and Cryospheric Sciences University of Innsbruck Innsbruck Austria.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Obleitner
authors.affiliation: Institute for Marine and Atmospheric Research Utrecht University of Utrecht Utrecht Netherlands.
authors.forename: Carleen H
authors.initials: CH
authors.lastname: Reijmer
authors.affiliation: Department of Earth Sciences Uppsala University Uppsala Sweden.
authors.forename: Veijo A
authors.initials: VA
authors.lastname: Pohjola
authors.affiliation: Institute of Geophysics Polish Academy of Sciences Warsaw Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Głowacki
authors.affiliation: Fram Centre Norwegian Polar Institute Tromsø Norway.
authors.forename: Jack
authors.initials: J
authors.lastname: Kohler
keywords: Arctic; RCM output; Svalbard; glacier mass balance; modeling