Inter-decadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures
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...
| Main Authors: | , |
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| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
International Glaciological Society
2016
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| Subjects: | |
| Online Access: | http://researchonline.ljmu.ac.uk/id/eprint/3103/ https://researchonline.ljmu.ac.uk/id/eprint/3103/1/Interdecadal%20variability%20of%20degree%20day%20factors%20on%20Vestari%20Hagafellsjohull.pdf http://www.igsoc.org/journal/accepted.html |
| Summary: | 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. |
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