Abstract
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.