Abstract
Abstract. Models of glacier surface melt are commonly used in studies of glacier mass balance and runoff; however, with limited data available, most models are validated based on ablation stakes and data from automatic weather stations (AWSs). The technological advances of unmanned aerial vehicles (UAVs) and structure from motion (SfM) have made it possible to measure glacier surface melt in detail over larger portions of a glacier. In this study, we use melt measured using SfM processing of UAV imagery to assess the performance of an energy balance (EB) and enhanced temperature index (ETI) melt model in two dimensions. Imagery collected over a portion of the ablation zone of Fountain Glacier, Nunavut, on 21, 23, and 24 July 2016 was previously used to determine distributed surface melt. An AWS on the glacier provides some measured inputs for both models as well as an additional check on model performance. Modelled incoming solar radiation and albedo derived from UAV imagery are also used as inputs for both models, which were used to estimate melt from 21 to 24 July 2016. Both models estimate total melt at the AWS within 16 % of observations (4 % for ETI). Across the study area the median model error, calculated as the difference between modelled and measured melt (EB = −0.064 m, ETI = −0.050 m), is within the uncertainty of the measurements. The errors in both models were strongly correlated to the density of water flow features on the glacier surface. The relation between water flow and model error suggests that energy from surface water flow contributes significantly to surface melt on Fountain Glacier. Deep surface streams with highly asymmetrical banks are observed on Fountain Glacier, but the processes leading to their formation are missing in the model assessed here. The failure of the model to capture flow-induced melt would lead to significant underestimation of surface melt should the model be used to project future change.
Highlights
The Canadian Arctic Archipelago holds approximately 14 % of the world’s area of glacier ice outside the major ice sheets, and rates of glacier melt in the region have increased since the late 1990s (Gardner et al, 2011, 2012; Noël et al, 2018; Lenaerts et al, 2013)
All four models capture daily patterns of melt, with lower melt totals on average in the second half of the month, which is consistent with lower solar radiation recorded at the automatic weather stations (AWSs) (Figs. 4a and 2b)
This study looks at a short time frame of only 3 d, weather conditions during the study are similar to those found throughout the ablation season on Fountain Glacier and are likely to be representative of average conditions throughout the season
Summary
The Canadian Arctic Archipelago holds approximately 14 % of the world’s area of glacier ice outside the major ice sheets, and rates of glacier melt in the region have increased since the late 1990s (Gardner et al, 2011, 2012; Noël et al, 2018; Lenaerts et al, 2013). Fisher et al (2012) show that recent melt rates on Canadian Arctic ice caps are the highest in 4000 years, while Gardner et al (2012) found that glaciers of the southern Canadian Arctic Archipelago contributed over 16 % of 2003–2010 sea-level rise. Given the importance of Canadian Arctic glaciers to global sea-level rise and the rapid change in melt rates observed in recent years, it is critical to better understand the processes contributing to melt rates on these glaciers. Direct measurements of melt rates on Arctic glaciers are scarce; only five glaciers from the Canadian Arctic have current data available online (WGMS, 2018). Bash et al, 2018; WGMS, 2018) These in situ measurements must be extrapolated to provide estimates of melt at other locations on a glacier or at other glaciers where no measurements exist.
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