Greenland Ice Sheet Surface Mass Balance Research Articles

Surface Mass Balance and Runoff Modeling Using HIRHAM4 RCM at Kangerlussuaq (Søndre Strømfjord), West Greenland, 1950–2080

Abstract A regional atmospheric model, the HIRHAM4 regional climate model (RCM) using boundary conditions from the ECHAM5 atmosphere–ocean general circulation model (AOGCM), was downscaled to a 500-m gridcell increment using SnowModel to simulate 131 yr (1950–2080) of hydrologic cycle evolution in west Greenland’s Kangerlussuaq drainage. Projected changes in the Greenland Ice Sheet (GrIS) surface mass balance (SMB) and runoff are relevant for potential hydropower production and prediction of ecosystem changes in sensitive Kangerlussuaq Fjord systems. Mean annual surface air temperatures and precipitation in the Kangerlussuaq area were simulated to increase by 3.4°C and 95 mm water equivalent (w.eq.), respectively, between 1950 and 2080. The local Kangerlussuaq warming was less than the average warming of 4.8°C simulated for the entire GrIS. The Kangerlussuaq SMB loss increased by an average of 0.3 km3 because of a 0.4 km3 rise in precipitation, 0.1 km3 rise in evaporation and sublimation, and 0.6 km3 gain in runoff (1950–2080). By 2080, the spring runoff season begins approximately three weeks earlier. The average modeled SMB and runoff is approximately −0.1 and 1.2 km3 yr−1, respectively, indicating that ∼10% of the Kangerlussuaq runoff is explained by the GrIS SMB net loss. The cumulative net volume loss (1950–2080) from SMB was 15.9 km3, and runoff was 151.2 km3 w.eq. This runoff volume is expected to have important hydrodynamic and ecological impacts on the stratified salinity in the Kangerlussuaq Fjord and on the transport of freshwater to the ocean.

Present and future climates of the Greenland ice sheet according to the IPCC AR4 models

The atmosphere–ocean general circulation models (AOGCMs) used for the IPCC 4th Assessment Report (IPCC AR4) are evaluated for the Greenland ice sheet (GrIS) current climate modelling. The most suited AOGCMs for Greenland climate simulation are then selected on the basis of comparison between the 1970–1999 outputs of the Climate of the twentieth Century experiment (20C3M) and reanalyses (ECMWF, NCEP/NCAR). This comparison indicates that the representation quality of surface parameters such as temperature and precipitation are highly correlated to the atmospheric circulation (500 hPa geopotential height) and its interannual variability (North Atlantic oscillation). The outputs of the three most suitable AOGCMs for present-day climate simulation are then used to assess the changes estimated by three IPCC greenhouse gas emissions scenarios (SRES) over the GrIS for the 2070–2099 period. Future atmospheric circulation changes are projected to dampen the zonal flow, enhance the meridional fluxes and therefore provide additional heat and moisture to the GrIS, increasing temperature over the whole ice sheet and precipitation over its northeastern area. We also show that the GrIS surface mass balance anomalies from the SRES A1B scenario amount to −300 km3/year with respect to the 1970–1999 period, leading to a global sea-level rise of 5 cm by the end of the 21st century. This work can help to select the boundaries conditions for AOGCMs-based downscaled future projections.

Greenland Ice Sheet surface mass‐balance modelling and freshwater flux for 2007, and in a 1995–2007 perspective

AbstractThe freshwater flux from the Greenland Ice Sheet (GrIS) to the ocean is of considerable importance to the global eustatic sea level rise. A physical modelling approach using SnowModel, a state‐of‐the‐art snow‐evolution modelling system that includes four submodels (MicroMet, EnBal, SnowPack, and SnowTran‐3D), was used to quantify the 1995–2007 GrIS surface mass‐balance (SMB), including freshwater flux. Meteorological observations from 26 meteorological stations located on the GrIS (Greenland Climate Network; GC‐Net stations) and in coastal Greenland (Danish Meteorological Institute (DMI) WMO‐stations) were used as model inputs. The GrIS minimum surface melt extent of 29% occurred in 1996, while the greatest extent of 51% was present in 2007. The 2007 melt extent was 20% greater than the average for 1995–2006. The year 2007 had the highest GrIS surface runoff (523 km3 y−1) and the lowest SMB (−3 km3 y−1); the only year with a negative GrIS SMB. Runoff in 2007 was approximately 35% greater than average for 1995–2006. From 1995 through 2007 overall, precipitation decreased while ablation increased, leading to an increased average SMB loss of 127 km3. The modelled GrIS SMB was merged with previous estimates of GrIS subglacial runoff (from geothermal melt) and GrIS calving to quantify GrIS freshwater flux to the ocean, indicating an average negative mass‐balance of 265 ( ±83) km3 y−1. This study further suggests an average GrIS freshwater flux of approximately 786 km3 y−1 to the ocean, of which 45% occurs from iceberg calving and geothermal bottom melting. The average annual GrIS freshwater flux equals 2·1 ± 0·2 mm w.eq. y−1 in eustatic sea level rise, indicating a cumulative flux of 28 mm w.eq. from 1995 through 2007. The average GrIS net loss contributes to a net sea level rise of 0·7 ± 0·2 mm w.eq. y−1, and a cumulative net increase of 10 mm w.eq. Copyright © 2009 John Wiley & Sons, Ltd.

Towards a re-assessment of the surface mass balance of the Greenland ice sheet

At present, the mass balance and especially the surface mass bal- ance of the Greenland Ice Sheet (GrIS) are poorly known. Current methods to determine GrIS surface mass balance as well as the inherent uncertainties are dis- cussed. Special emphasis is placed on the increasingly important role of regional atmospheric climate models, which explicitly calculate the individual components of the surface mass balance: (solid) precipitation, melt and subsequent runoff, sublimation/deposition and refreezing in the snow. Especially the latter term is very uncertain, and poses a great challenge to modellers. Some recent advances in these fields of research are presented.

Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries

Abstract. Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty.