PhD (Funded by PMRF)

Spatial Downscaling of GRACE Water Storage Changes

Terrestrial Water Storage Change (TWSC) is obtained from Gravity Recovery and Climate Experiment (GRACE) and its successor mission GRACE Follow-On (GRACE-FO). It is currently the only source of direct observation of this state variable. The most significant limitation in the applications of this dataset is its coarse spatial resolution, which is primarily due to the low satellite altitude making it most sensitive to large-scale mass changes. Further filtering to remove correlated noise deteriorates this resolution by an effect called leakage. Leakage causes scattering of mass changes from its true location to neighboring regions. Spatial downscaling, hence, is required to use this dataset in small-scale studies like water budget closure in a basin. Pattern scaling and Statistical downscaling are two popular approaches that have been employed. Both the approaches rely on high-resolution estimates of water storage changes from hydrology models. My research aims to present a novel method that combines both approaches, suppressing the limitations in each. The transfer function being used for statistical downscaling is the partial lease squares regression, introduced recently to GRACE by Vishwakarma et.al, 2021. This work is an extension of my work with scaling factors, done as a master's project in Germany.

Study Region

Currently, the study region is the Indus basin in southeast Asia, covering an area of 1.14 Mkm2. However, the study region is only for experimenting and testing the method. The actual plan is to present a global downscaled product, once the results in Indus basin are satisfactory. 

Masters (Funded by DAAD and MHRD)

Scaling Factor Approach for Leakage Correction of GRACE mass changes in Indus Basin

This study was conducted under the DAAD Kombinierte Studien- und Praxisaufenthalte für Ingenieure aus Entwicklungsländern (KOSPIE) Grant 2019 as a master’s project at Technische Universität Dresden, Institut für Planetare Geodäsie, Chair of Geodetic Earth System Research. The scaling factor approach was studied, for leakage correction in Total Water Storage (TWS) estimates for Indus basin derived from Gravity Recovery and Climate Experiment (GRACE) spherical harmonic (SH) data. It was extended as a potential downscaling method during the first year of PhD. The WaterGAP Hydrology Model (WGHM v2.2d) with its two variants, standard, without glacier mass changes and Integrated, with glacier mass changes, was used to develop scaling factors. Three schemes of scaling were explored; Basin scaling, Gridded scaling, and Frequency-dependent scaling. The study resulted in a research paper that is under review with the Hydrology and Earth System Science journal.

Publications/Conferences

1. Tripathi, V., Vishwakarma, B. D., and Horwath, M.: Data-Driven and Scaling Factor methods of GRACE leakage correction: Can they be reconciled?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12485, https://doi.org/10.5194/egusphere-egu23-12485, 2023. 

2. Tripathi, V., Groh, A., Horwath, M., and Ramsankaran, R.: Scaling methods of leakage correction in GRACE mass change estimates revisited for the complex hydro-climatic setting of the Indus Basin, Hydrol. Earth Syst. Sci., 26, 4515–4535, https://doi.org/10.5194/hess-26-4515-2022, 2022. 

3. Tripathi V. (2020, November 18–20). The Present & Future of Satellite Gravimetry – An online workshop on the design, development and applications of satellite gravimetry [Conference presentation]. SatGrav 2020, IIT Kanpur, India. (https://satgrav2020.tuxfamily.org/posts/terrestrial-water-storage-change-of-the-indus-basin-derived-from-grace-spherical-harmonics-and-mascon-solutions/)

Some Figures from my Studies

*Due to the nature of ongoing PhD work which is quite novel, I cannot publish my most recent figures publicly!