Global Assessment of Supraglacial Debris-Cover Extents

Rocky debris on glacier surfaces influences ice melt rates and the response of glaciers to climate change. However, scarce data on the extent and evolution of supraglacial debris cover have so far limited its inclusion in regional to global glacier models. Here we present global data sets of supraglacial debris-cover extents, based on Landsat 8 and Sentinel-2 optical satellite imagery. We find that about 4.4% (similar to 26,000 km(2)) of all glacier areas (excluding the Greenland ice sheet and Antarctica) are covered with debris, but that the distribution is heterogeneous. The largest debris-covered areas are located in high-mountain ranges, away from the poles. At a global scale, we find a negative scaling relationship between glacier size and percentage of debris. Therefore, the influence of debris cover on glacier mass balances is expected to increase in the future, as glaciers continue to shrink. Plain Language Summary Most of the melting of land-terminating glaciers occurs at their surface. In mountainous regions, these ice surfaces are often partly covered by rocks and sediments (debris), which can amplify, or reduce, ice melt rates, depending on debris thickness. So far, however, debris cover is rarely taken into account in models of how glaciers respond to climate change. New global data sets of debris-cover extents, based on high-resolution satellite imagery, indicate that similar to 4.4% of all glacier surfaces (excluding the Greenland ice sheet and Antarctica) are covered with debris. Debris cover is particularly common in high and steep mountain ranges but is rare in low-relief landscapes, closer to the poles. Our findings provide a basis for including debris-cover effects in regional to global glacier models.