Characterization of runoff-storage relationships in boreal catchments

Abstract

Due to global warming, Arctic sea ice has been shrinking steadily in recent decades, which is a concern to scientists and society. Freshwater inflow is crucial for the formation and preservation of sea ice, therefore the understanding of its status is helpful to assess the possible impact of sea ice decline in the Arctic sea. Due to the continuous reduction of the gauging stations for river discharge, the scientists began to develop other methods like using spaceborne data to replace or supplement in situ measurements. This study aims at characterizing the runoff-storage (R-S) relationships in boreal catchments. GRACE observations of the time-dependent gravity field provide us with the measurements for the state of total water storage on land masses, which allow for a direct comparison of monthly runoff and water storage. Investigation of the R-S relationship in boreal catchments shows a distinct periodic behavior with a hysteresis. Motivated by the work of Riegger and Tourian (2014), the hypothesis of a R-S relationship characterized by the superposition of linear contributions from coupled/liquid storage and nonlinear contributions from uncoupled storage is investigated by means of remote sensing. MODIS snow coverage data is used to separate total water storage into liquid part and solid part. After a least-squares linear fit, the non-linear part of the RS relationship can be fully assigned to the solid storage while runoff and liquid storage can be characterized as a LTI system. This can then be used for direct determination of river runoff from GRACE mass and vice versa.