Characterisation of Runoff – Storage Relationships By Satellite-Gravimetry and Remote Sensing

Wednesday, 17 December 2014: 11:35 AM
Johannes M. Riegger, University of Stuttgart, Institute for Modelling Hydraulic and Environmental Systems, Stuttgart, Germany and Mohammad J. Tourian, University of Stuttgart, Institute of Geodesy, Stuttgart, Germany
GRACE observations of the time dependent gravity field provide a direct measurement of the monthly state of mass and thus monthly total water storage in a catchment. This for the first time allows for a direct comparison of monthly runoff and water storage.

Investigations of global scale Runoff-Storage (R-S) relationships for different climatic conditions show distinct periodic characteristics with hysteresis for total water storage.

For fully humid tropical catchments hysteresis reveals a time invariant temporal delay from storage to runoff. An adjustment of time lag leads to a linear (R-S) relationship with correlation 0.98. Confirmed by the coherence of Fourier spectra, this allows to characterize this R-S relationship as a Linear Time invariant System (LTI).

Based hereon, the hypothesis of a R-S relationship characterized by the superposition of linear contributions from coupled/liquid storage and nonlinear contributions from uncoupled storages is investigated by means of remote sensing.

For boreal catchments MODIS snow coverage is used to separate total storage into coupled/liquid and uncoupled/solid components either directly by assigning frozen solid storage to the snow covered areas or indirectly by a model based aggregation of snow and liquid according to snow coverage. Both methods show, that the nonlinear part of the R-S relationship can be fully assigned to the uncoupled/solid storage while the relationship of runoff and liquid storage can also be characterized as LTI.

This system behavior thus allows for a direct determination of river runoff from GRACE mass or vice versa of water storage from measured runoff for unmanaged catchments, provided that the coupled/uncoupled storage components can be quantified by remote sensing.

Examples for river runoff time series determined from GRACE mass are presented for Amazon sub-catchments and with the additional integration of MODIS snow coverage also for the boreal catchments of Sibiria and North America.