1Climate, Ocean, and Sea Ice Modeling Group, Computational Physics and Methods (CCS-2), Los Alamos National Laboratory, New Mexico, USA
2Cooperative Institute for Research in the Atmosphere,Colorado State University, Colorado, USA
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Colorado, USA
4Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Holland
5Department of Geography and Geology, University of Copenhagen, Copenhagen, Denmark
Abstract. This observation and modeling study provides insights into runoff exiting the Watson River drainage basin, Kangerlussuaq, West Greenland during a 30 year period (1978/79–2007/08) when the climate experienced increasing temperatures and precipitation. The 30-year simulations quantify the terrestrial freshwater output from part of the Greenland Ice Sheet (GrIS) and the land between the GrIS and the ocean, in the context of global warming and increasing GrIS surface melt. We used a snow-evolution modeling system (SnowModel) to simulate the winter accumulation and summer ablation processes, including runoff and surface mass balance (SMB), of the ice sheet. To a large extent, the SMB fluctuations could be explained by changes in net precipitation (precipitation minus evaporation and sublimation), with 8 out of 30 years having negative SMB, mainly because of relatively low annual net precipitation. The overall trend in net precipitation and runoff increased significantly, while SMB increased insignificantly throughout the simulation period, leading to enhanced precipitation of 0.59 km3 w.eq. (or 60%), runoff of 0.43 km3 w.eq. (or 54%), and SMB of 0.16 km3 w.eq. (or 86%). Runoff rose on average from 0.80 km3 w.eq. in 1978/79 to 1.23 km3 w.eq. in 2007/08. The percentage of catchment outlet runoff explained by runoff from the GrIS decreased on average ∼10%.