The hydrological budget over Pan-Arctic river basins from GRACE and re-analysis: variability, trends and uncertainties from 2003-2009

High-resolution retrievals of recent changes in the Earth’s gravity field using GRACE (Gravity Recovery and Climate Experiment) offer insights into the water exchange between the atmosphere, ocean, and terrestrial reservoirs. Here, we focus on the Pan-Arctic region, where water/ice mass fluxes and sea ice cover are rapidly changing, and combine this space geodetic data set with estimates of the atmospheric precipitation and evaporation fluxes from re-analysis data sets (ERA-Interim and JRA-25) to determine variations and trends in freshwater river discharge from the entire Pan-Arctic river basins into the Arctic Ocean from 2003 to 2009. As GRACE has now completed 7 years of time-variable gravity measurements, this analysis yields new quantitative insights into annual to inter-annual dynamics of the Pan-Arctic hydrologic mass-balance, including regions of un-gauged freshwater discharge into the Arctic Ocean. For the main drainage basins for which direct discharge observations are available, our analysis yields good agreement between observed and remotely sensed estimates during summer months, but also consistently low-biased estimates during winter. Using different re-analysis and gridded precipitation data sets, we investigate possible sources of uncertainty and biases, and discuss the influence of these freshwater fluxes on climate and circulation changes in the Arctic Ocean.