14 Feb 2022
14 Feb 2022
Status: this preprint is currently under review for the journal HESS.

Scaling methods of leakage correction in GRACE mass change estimates revisited for the complex hydro-climatic setting of the Indus basin

Vasaw Tripathi1, Andreas Groh2, Martin Horwath2, and RAAJ Ramsankaran1 Vasaw Tripathi et al.
  • 1Hydro-Remote Sensing Applications (H-RSA) Group, Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, Maharashtra, India
  • 2Institut für Planetare Geodäsie, Technische Universität Dresden, Germany

Abstract. Total Water Storage Change (TWSC) reflects the balance of all water fluxes in a hydrological system. The Gravity Recovery and Climate Experiment/Follow-On (GRACE/GRACE-FO) satellite missions are the only means of observing this state variable, distributed as coefficients of a spherical harmonic (SH) model. The well-known correlated noise in these observations requires filtering, scattering the actual mass changes from their true locations. This effect is known as leakage. This study explores the traditional basin and grid scaling approaches and develops a novel frequency-dependent scaling for leakage correction of GRACE TWSC in a unique, basin-specific assessment for the Indus basin. We harness the characteristics of significant heterogeneity in the Indus basin due to climate and human-induced changes to evaluate the physical nature of these scaling schemes. The most recent, WaterGAP Hydrology Model (WGHM v2.2d), with its two variants, standard (without glacier mass changes) and Integrated (with glacier mass changes), is used to derive scaling factors. For the first time, we explicitly show the effect of inclusion or exclusion of glacier mass changes in the model on the gridded scaling factors. Frequency dependant scaling factors, as a novelty, allow us to compare the differences of scaling seasonal and trend components separately. We employ time series analysis using the Lomb-Scargle periodogram to decompose the time series and visualize the effect of filtering on different time scales. We find that for the Indus basin, where mass changes of different frequencies are localized, frequency-dependent scaling factors for the entire basin perform similar to the gridded scaling factors, while both outperform basin scaling. The property of frequency-dependent scaling to keep the noise level unscaled can be extremely useful for applications requiring a high signal-to-noise ratio of TWSC observations. Apart from these novel developments and insights into the traditional scaling approach, our study encourages the regional scale users to conduct specific assessments for their basin of interest.

Vasaw Tripathi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2022-43', A. P. Dimri, 11 Mar 2022
  • RC2: 'Review on hess-2022-43', Henryk Dobslaw, 31 Mar 2022
  • EC1: 'Comment on hess-2022-43', Narendra Das, 19 May 2022

Vasaw Tripathi et al.

Vasaw Tripathi et al.


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Short summary
GRACE/GRACE-FO provided global observations of water storage change since 2002. Scaling is a common approach to compensate for the spatial filtering inherent to the results. However, for complex hydrological basins, the compatibility of scaling with the characteristics of regional hydrology has been rarely assessed. We assess traditional scaling approaches and a new scaling approach for the Indus basin. Our results will help users with regional focus understand implications of scaling choices.