Estimating runoff from pan-Arctic basins through an improved runoff-storage relationship using satellite gravimetry in the GRACE period 2002-2019

Spaceborne gravimetry is the only satellite method that can observe terrestrial water storage at a continental scale. The time variable gravity field, observed by GRACE and GRACE-FO, is a measure of mass transport primarily in the global water cycle. In this contribution we analyse the runoff-storage relationship in the GRACE time frame for the pan-Arctic drainage basins. Over these boreal catchments, the conventional hysteresis-type formulation requires algorithmic adaptations in order to accommodate snowload and base-flow during winter periods. We show that the parameters involved in the pan-Arctic runoff-storage relationships are transferable, albeit with a few exceptions, between the various catchments. This remarkable fact allows us access to determining runoff from ungauged drainage areas across the pan-Arctic. As a result we can quantify the total freshwater flux from pan-Arctic basins into the Arctic Ocean.