摘要：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.
关键词：energy balance; glacier meteorology; ice and climate; ice; sheet mass balance; melt; surface
