Assessing bare-ice albedo simulated by MAR over the Greenland ice sheet (2000–2021) and implications for meltwater production estimates

Abstract. Surface mass loss from the Greenland ice sheet (GrIS) has
accelerated over the past decades, mainly due to enhanced surface melting
and liquid water runoff in response to atmospheric warming. A large portion
of runoff from the GrIS originates from exposure of the darker bare ice in
the ablation zone when the overlying snow melts, where surface albedo plays
a critical role in modulating the energy available for melting. In this
regard, it is imperative to understand the processes governing albedo
variability to accurately project future mass loss from the GrIS. Bare-ice
albedo is spatially and temporally variable and contingent on non-linear
feedbacks and the presence of light-absorbing constituents. An assessment of
models aiming at simulating albedo variability and associated impacts on
meltwater production is crucial for improving our understanding of the
processes governing these feedbacks and, in turn, surface mass loss from
Greenland. Here, we report the results of a comparison of the bare-ice
extent and albedo simulated by the regional climate model Modèle
Atmosphérique Régional (MAR) with satellite imagery from the
Moderate Resolution Imaging Spectroradiometer (MODIS) for the GrIS below
70∘ N. Our findings suggest that MAR overestimates bare-ice albedo
by 22.8 % on average in this area during the 2000–2021 period with respect
to the estimates obtained from MODIS. Using an energy balance model to
parameterize meltwater production, we find this bare-ice albedo bias can
lead to an underestimation of total meltwater production from the bare-ice
zone below 70∘ N of 42.8 % during the summers of 2000–2021.