Comparing simple albedo scaling methods for estimating Arctic glacier mass balance

Mass balance measurements in the Canadian Arctic are limited, particularly for smaller glaciers, which introduces significant uncertainties in regional mass balance assessment. Here we report on the correlations between Moderate Resolution Imaging Spectroradiometer (MODIS) Terra albedo measurements (Version 6) and net annual mass balance for five glaciers in the Canadian Arctic over the period 2002-2016. Three glacier albedo aggregation methods are tested for the melt season (June, July and August): minimum, raw average, and interpolated average. These are evaluated in terms of a 53-71% reduction in observations due to cloud cover in the raw albedo time series. For the minimum method, the whole glacier albedo is calculated from the average of the minimum melt season albedo of each grid cell, irrespective of the day on which they occurred, resulting in R-2 values between 0.20 and 0.87. In the raw average method, averaging all albedo values within a glacier outline over the melt season improves the correlation to mass balance to a range of 0.61-0.95. In the interpolated average method, linear interpolation of the raw average albedo values to fill cloud gaps, then averaging them, improves the raw average correlations for all ice masses by similar to 5% (R-2 range 0.68-0.97). Overall, the interpolated average albedo method performs substantially better for the smallest glacier than the minimum or the raw average methods. The most negative net mass balance occurs at Grise Fiord Glacier, which is the smallest (<4.0 km(2)), but not the lowest elevation, glacier analysed. For this glacier, the interpolated average albedo improves the correlation with mass balance to an R-2 = 0.68 (p-value < .05), compared to an R-2 = 0.17 for the minimum albedo method (p-value > .05). When the five glaciers' interpolated average albedo is correlated to their ensemble mass balance, an R-2 = 0.82 is achieved. These results show that interpolated MODIS Terra melt season albedo measurements can realistically approximate net annual glacier mass balance for Arctic glaciers and ice caps, without additional information about precipitation or temperature, and in the absence of a melt model.