| dc.description.abstract | Increase in surface melting is the main contributor to Greenland Ice Sheet (GrIS)
mass loss, therefore its quantification is extremely relevant in assessing the future
rise of sea levels. However, direct measurements of surface melt and runoff are
difficult and present many gaps in time and space. Therefore, numerical modeling
is essential to calculate melt and assess the current state of the GrIS Surface Mass
Balance (SMB), which is the sum of the mass fluxes removing or accumulating mass
at the ice-sheet surface. Besides this, the last decades have been marked by a shift
in the atmospheric circulation over Greenland, with more negative North Atlantic
Oscillation (NAO) phases and higher frequency blocking events during summer that
increased the Greenland Blocking Index (GBI). These accompany the decrease in
SMB, bringing relatively warm and moist air towards the GrIS. This study uses the
latest output of the Regional Atmospheric Climate Model RACMO2.4p1 (5.5 km
horizontal resolution) and observations from selected Automatic Weather Stations
(AWSs) and annual stakes measurements to: (1) evaluate the model performance;
(2) reconstruct the GrIS integrated Surface Mass Balance (SMB) and its components
from 1945 to 2023; (3) relate the interannual variability of SMB and SMB components
to GBI variability, highlighting the connections between summer melt and higher
GBI values. The results show that (1) RACMO2.4p1 underestimates the net shortwave
radiation (-3 W/m2) due to a delayed onset of the melting season. The SHF
is also underestimated (-2 W/m2), hence leading overall to an underestimation of
melt energy, especially in the low-lying stations (i.e. KAN_L, QAS_L, TAS_L),
for which the SMB bias between modeled and observed annual SMB is higher (0.1
m w.e. yr−1 for stations above 1000 m a.s.l. vs. 1.7 m w.e. yr−1 below 1000 m
a.s.l.). (2) The modeled GrIS integrated SMB between 1945 and 2023 is 491 Gt
yr−1, the integrated runoff is 257 Gt yr−1 and the integrated accumulation is 822 Gt
yr−1. The rate of integrated SMB decline accelerated from 1982, which marks the
onset of a series of climatological periods characterized by the most rapid decreases
in SMB. (3) Finally, the SMB is anti-correlated to the summer GBI (R2=-0.67)
through the correlation between summer melt and summer GBI (R2=0.85). Both correlations show different spatial sensitivity to GBI, whereas the integrated SMB
shows a decrease of 102 Gt/yr when the summer GBI increases by one-standarddeviation.
Therefore, this study highlights the important relationship between SMB
and summer GBI, and the necessity of realistically simulating regional circulation
variability to model future GrIS SMB, as much as refining RACMO2.4p1 to better
constrain the current state of the GrIS SMB. | |
