Paul Halas

and 3 more

Surface runoff over the Greenland Ice Sheet has been shown to have an impact on ice velocities, both at short as well as decadal timescales. While the short timescales are necessary to comprehend the physical processes connecting subglacial water pressure and ice motion, upscaling to longer timescales is paramount to assessing the future behavior of glaciers in a warming climate. In this study, we assess in a land-terminating part of Southwest Greenland over 2013-2021 the relationship between annual ice velocities derived from optical feature-tracking and surface runoff derived from the ERA5-MAR climate model. The recent time period, providing frequent satellite acquisition, allows for a precise selection of image pairs, while also covering summer melt seasons varying in both intensity and duration. We find that the exact link between runoff anomalies and ice velocity anomalies changes depending on the basin considered and that the relationship also changes with altitude. However, all basins do show a similar overall behavior: at low elevations, while a small increase in runoff leads to faster velocities, a large increase in runoff leads to a slowdown of the glacier ice, but years with even larger runoff would tend to make the ice faster again. As altitude increases, runoff anomalies variations seem to have less impact on ice velocities. We compute for each pixel a simple index to quantify this relationship, presenting here a map displaying how runoff anomalies affected the velocities in 2013-2021 and underlining the spatially varying impact of meltwater depending on altitude and location.