Interdecadal variability of degree-day factors on Vestari Hagafellsjökull (Langjökull, Iceland) and the importance of threshold air temperatures
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...
| Published in: | Journal of Glaciology |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Cambridge University Press (CUP)
2016
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1017/jog.2016.21 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143016000216 |
| Summary: | 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. |
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