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Inter-decadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures

Matthews, TR and Hodgkins, R (2016) Inter-decadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures. Journal of Glaciology, 62 (232). pp. 310-322. ISSN 1727-5652

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Abstract

The skill of degree-day glacier melt models is highly dependent on the choice of degree-day factor (DDF), which is often assumed to remain constant in time. Here we explore the validity of this assumption in a changing climate for two locations on Vestari Hagafellsjökull (1979-2012) using a Surface Energy Balance (SEB) approach that isolates the effect of changes in the prevailing weather on the DDF. At lower-elevation, we observe stable DDF during the period of study; however, at higher elevation, DDF is noted to be more variable and a statistically-significant downward trend is observed. This is found to result from an inappropriate threshold air temperature (T_crit) from which to initiate the positive-degree-day sum, and is removed by setting T_crit to -1.83°C, rather than the usual value of 0°C used in degree-day melt models. The stationarity of DDF once T_crit is adjusted contradicts previous research and lends support to the use of constant DDF for projecting future glacier melt. Optimizing T_crit also improves the skill of melt simulations at our study sites. This research thus highlights the importance of T_crit for both melt model performance and the evaluation of DDF stationarity in a changing climate.

Item Type: Article
Uncontrolled Keywords: 0406 Physical Geography And Environmental Geoscience
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
Divisions: Natural Sciences and Psychology
Publisher: International Glaciological Society
Date Deposited: 08 Mar 2016 15:37
Last Modified: 06 Sep 2017 23:10
URI: http://researchonline.ljmu.ac.uk/id/eprint/3103

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