Quantifying Energy and Mass Fluxes Controlling Godthåbsfjord Freshwater Input in a 5-km Simulation (1991–2012)*,+

Abstract

Freshwater runoff to fjords with marine-terminating glaciers along the Greenland Ice Sheet margin has an impact on fjord circulation and potentially ice sheet mass balance through increasing heat transport to the glacier front. Here, the authors use the high-resolution (5.5 km) HIRHAM5 regional climate model, allowing high detail in topography and surface types, to estimate freshwater input to Godthåbsfjord in southwest Greenland. Model output is compared to hydrometeorological observations and, while simulated daily variability in temperature and downwelling radiation shows high correlation with observations (typically >0.9), there are biases that impact the results. In particular, overestimated albedo leads to underestimation of melt and runoff at low elevations. In the model simulation (1991–2012), the ice sheet experiences increasing energy input from the surface turbulent heat flux (up to elevations of 2000 m) and shortwave radiation (at all elevations). Southerly wind anomalies and declining cloudiness due to an increase in atmospheric pressure over north Greenland contribute to increased summer melt. This results in declining surface mass balance (SMB), increasing surface runoff, and upward shift of the equilibrium line altitude. SMB is reconstructed back to 1890 though regression between simulated SMB and observed temperature and precipitation, with added uncertainty in the period 1890–1952 because of possible inhomogeneity in the precipitation record. SMB as low as in recent years appears to have occurred before, most notably around 1930, 1950, and 1960. While previous low SMBs were mainly caused by low accumulation, those around 1930 and in the 2000s are mainly due to warming.

Glacial meltwater and primary production are drivers of strong CO<sub>2</sub> uptake in fjord and coastal waters adjacent to the Greenland Ice Sheet

“…Recent hydrological simulations estimate the annual freshwater input to Godthåbsfjord (excluding solid ice discharge as well as submarine melt from glaciers) to be 22.5±5.2 km 3 yr −1 for the period 1991-2012 (Langen et al, 2014). Ice sheet runoff accounts for 60 % of the freshwater input, land runoff is responsible for 34 %, and net precipitation over the fjord surface represents the remaining 6 % (Langen et al, 2014). project a similar estimate of 10-20 km 3 glacial ice loss per year (solid ice discharge, surface ice melt and submarine melt) for the Godthåbsfjord glaciers.…”

21st-century climate change around Kangerlussuaq, west Greenland: From the ice sheet to the shores of Davis Strait

“…Compared with the HIRHAM5 version described in Christensen et al (2006), a dynamic snow/ice scheme together with an updated snow/ice albedo scheme have been included in the model runs used in this study (see Langen et al 2015Langen et al , 2017 for details). (b, bottom).…”

“…A comparison of the performance of early versions of these RCMs in Rae et al (2012) showed some differences in performance. However, analysis by Mottram et al (2017) and Vernon et al (2013) shows that these RCMs produce similar values for surface mass balance over the ice sheet as a whole, although with some significant differences in the components of mass balance and in the spatial distribution of these components (e.g., Langen et al 2015;Van As et al 2014), partly attributable to different model resolution as well as different ice masks and potentially different parameterization schemes. Here, we focus on validating the HIRHAM5 simulations against observations, excluding a comparison with previous high-resolution downscalings.…”

“…More recently, Langen et al (2015) used a detailed and updated version of RCM HIRHAM5 (Christensen et al 2006) with high resolution (5.5 km), driven by reanalysis data (ERA-Interim; Dee et al 2011) covering the whole of Greenland, to estimate the changes in icesheet surface mass balance for the drainage basin linked to the Godthåbsfjord. The HIRHAM5 model has been further refined with a number of additions that include a more sophisticated snow scheme suited to accurately capturing albedo feedbacks and processes within the snowpack (see Langen et al 2017 for details).…”

“…The performance of the HIRHAM5 RCM, driven by the ERA-Interim reanalysis, has been fully evaluated by Langen et al (2015Langen et al ( , 2017 and by Mottram et al (2017), showing that the ice sheet is well represented during present-day conditions with a surface mass balance in the ablation area close to observations but with an underestimation of the interannual variability of the number of melt days. We here use weather station observations to also evaluate the performance of the HIRHAM5 when forced with the EC-Earth historical scenario in order to validate the use of the ECEarth GCM as forcing at the lateral boundaries.…”