The modelled surface mass balance of the Antarctic Peninsula at 5.5¯km horizontal resolution

This study presents a high-resolution (5.5 km) estimate of surface mass balance (SMB) over the period 1979-2014 for the Antarctic Peninsula (AP), generated by the regional atmospheric climate model RACMO2.3 and a firn densification model (FDM). RACMO2.3 is used to force the FDM, which calculates processes in the snowpack, such as meltwater percolation, refreezing and runoff. We evaluate model output with 132 in situ SMB observations and discharge rates from six glacier drainage basins, and find that the model realistically simulates the strong spatial variability in precipitation, but that significant biases remain as a result of the highly complex topography of the AP. It is also clear that the observations significantly underrepresent the highaccumulation regimes, complicating a full model evaluation. The SMB map reveals large accumulation gradients, with precipitation values above 3000mmwe yr-1 in the western AP (WAP) and below 500mmwe yr-1 in the eastern AP (EAP), not resolved by coarser data sets such as ERA-Interim. The average AP icesheet-integrated SMB, including ice shelves (an area of 4.1105 km2), is estimated at 351 Gt yr-1 with an interannual variability of 58 Gt yr-1, which is dominated by precipitation (PR) (365±57 Gt yr-1). The WAP (2.4×105 km2) SMB (276±47 Gt yr-1), where PR is large (276±47 Gt yr-1), dominates over the EAP (1.7×105 km2) SMB (75±11 Gt yr-1) and PR (84±11 Gt yr-1). Total sublimation is 11±2 Gt yr-1 and meltwater runoff into the ocean is 4±4 Gt yr-1. There are no significant trends in any of the modelled AP SMB components, except for snowmelt that shows a significant decrease over the last 36 years (-0.36 Gt yr-2)