End‐of‐winter snow depth variability on glaciers in Alaska

Abstract

A quantitative understanding of snow thickness and snow water equivalent (SWE) on glaciers is essential to a wide range of scientific and resource management topics. However, robust SWE estimates are observationally challenging, in part because SWE can vary abruptly over short distances in complex terrain due to interactions between topography and meteorological processes. In spring 2013, we measured snow accumulation on several glaciers around the Gulf of Alaska using both ground-and helicopter-based ground-penetrating radar surveys, complemented by extensive ground truth observations. We found that SWE can be highly variable (40% difference) over short spatial scales (tens to hundreds of meters), especially in the ablation zone where the underlying ice surfaces are typically rough. Elevation provides the dominant basin-scale influence on SWE, with gradients ranging from 115 to 400 mm/100 m. Regionally, total accumulation and the accumulation gradient are strongly controlled by a glacier's distance from the coastal moisture source. Multiple linear regressions, used to calculate distributed SWE fields, show that robust results require adequate sampling of the true distribution of multiple terrain parameters. Final SWE estimates (comparable to winter balances) show reasonable agreement with both the Parameter-elevation Relationships on Independent Slopes Model climate data set (9-36% difference) and the U.S. Geological Survey Alaska Benchmark Glaciers (6-36% difference). All the glaciers in our study exhibit substantial sensitivity to changing snow-rain fractions, regardless of their location in a coastal or continental climate. While process-based SWE projections remain elusive, the collection of ground-penetrating radar (GPR)-derived data sets provides a greatly enhanced perspective on the spatial distribution of SWE and will pave the way for future work that may eventually allow such projections.

Mass Balance Evolution of Black Rapids Glacier, Alaska, 1980–2100, and Its Implications for Surge Recurrence

“…The annual balances of the two glaciers each describe 75% of the other's balance variability (r 2 = 0.75, Figure 11B), which is notable given the different properties (size, geometry, debris cover) of the two glaciers . As expected, the summer balances of the two glaciers correlate much better (r 2 = 0.81) than the winter balances (r 2 = 0.36), the latter of which are more dependent on local conditions (e.g., topography, McGrath et al, 2015). Comparison of the summer season lengths ( Figure 11C) indicates a very good match after 1995, but more variability before that, mostly due to differences in the start of the summer seasons.…”

High‐resolution modeling of coastal freshwater discharge and glacier mass balance in the Gulf of Alaska watershed

“…The computed gradients in annual precipitation ranged from 0.7 m km −1 at Gulkana Glacier to 2.5 m km −1 at Mendenhall Glacier, similar to measured SWE gradients (1.15–4.0 m km −1 ) for GOA glaciers reported in McGrath et al . [].…”

Mass Balance Re-analysis of Findelengletscher, Switzerland; Benefits of Extensive Snow Accumulation Measurements

“…This could be improved by including extensive measurements of winter mass balance, assimilated into a mass balance model to derive the temporal evolution of accumulation and ablation. Previous studies suggest that such extensive winter balance observations can be obtained, for instance, by helicopterborne ground-penetrating radar in addition to conventional snow probings and density pits (Machguth et al, 2006a;Sold et al, 2013;Gusmeroli et al, 2014;McGrath et al, 2015).…”