Characterization of runoff-storage relationships by satellite gravimetry and remote sensing

• Published in: Water resources research 2014-04, Vol.50 (4), p.3444-3466
• Main Authors: Riegger, J., Tourian, M. J.
• Format: Article
• Language: English
• Subjects: Catchments; Climatic conditions; Freshwater; GRACE; Gravimetry; MODIS; Remote sensing; River flow; Runoff; runoff-storage-relationship; Satellites; Snow; Spectral analysis; storage; Water storage
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2013WR013847

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. Our spectral analysis supports the fact that the R‐S relationships can be characterized as a Linear Time Invariant (LTI) System. As a consequence in time domain an adjustment of time lag leads to correlation of 0.98 between runoff and storage. 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 an LTI system. This system behavior thus allows for a direct determination of river runoff from GRACE mass and vice versa for unmanaged catchments, provided that the coupled/uncoupled storage components can be quantified remote sensing. Key Points Identification of linear relationship between runoff and coupled storage Quantification of time lag between storage and runoff for large‐scale systems Separation of uncoupled/coupled storage by GRACE and remote sensing