Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2017-146
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Mar 2017
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products
Mohammad Shamsudduha1,2, Richard G. Taylor2, Darren Jones3, Laurent Longuevergne4, Michael Owor5, and Callist Tindimugaya6 1Institute for Risk and Disaster Reduction, Universi ty College London, UK
2Department of Geography, University College London, UK
3Centre for Geography, Environment and Society, University of Exeter, UK
4CNRS – UMR 6118 Géosciences Rennes, Université de Rennes 1, France
5Department of Geology & Petroleum Studies, Makerere University, Uganda
6Directorate of Water Resources Management, Ministry of Water & Environment, Uganda
Abstract. GRACE (Gravity Recovery and Climate Experiment) satellite data monitor large-scale changes in total terrestrial water storage (ΔTWS) providing an invaluable tool where in situ observations are limited. Substantial uncertainty remains, however, in the amplitude of GRACE gravity signals and the disaggregation of ΔTWS into individual terrestrial water stores (e.g. groundwater storage). Here, we test the phase and amplitude of GRACE ΔTWS signals from 5 commonly-used gridded products (i.e., NASA's GRCTellus: CSR, JPL GFZ; JPL-Mascons; GRGS GRACE) using in situ data and modelled soil-moisture from the Global Land Data Assimilation System (GLDAS). The focus of this analysis is a large and accurately observed reduction in ΔTWS of 75 km3 from 2004 to 2006 in Lake Victoria in the Upper Nile Basin. We reveal substantial variability in current GRACE products to quantify the reduction of ΔTWS in Lake Victoria that ranges from 68 km3 (GRGS) to 50 km3 and 26 km3 for JPL-Mascons and GRCTellus, respectively. Representation of the phase in ΔTWS in the Upper Nile Basin by GRACE products varies but is generally robust with GRGS, JPL-Mascons and GRCTellus (ensemble mean of CSR, JPL and GFZ time-series data) explaining 91 %, 85 %, and 77 % of the variance, respectively, in in-situ ΔTWS. Resolution of changes in groundwater storage (ΔGWS) from GRACE ΔTWS is greatly constrained by both uncertainty in modelled changes in soil-moisture storage (ΔSMS) and the low annual amplitudes in ΔGWS (e.g., 3.5 to 4.4 cm) observed in deeply weathered crystalline rocks underlying the Upper Nile Basin. Our study highlights the substantial uncertainty in the amplitude of ΔTWS that can result from different data-processing strategies in commonly used, gridded GRACE products.

Citation: Shamsudduha, M., Taylor, R. G., Jones, D., Longuevergne, L., Owor, M., and Tindimugaya, C.: Recent changes in terrestrial water storage in the Upper Nile Basin: an evaluation of commonly used gridded GRACE products, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-146, in review, 2017.
Mohammad Shamsudduha et al.
Mohammad Shamsudduha et al.
Mohammad Shamsudduha et al.

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Short summary
This study tests the ability of five commonly used GRACE satellite datasets to measure a large and accurately observed reduction in water storage of 75 km3 that occurred in the Lake Victoria Basin of East Africa from 2004 to 2006. Substantial differences among the datasets to represent the amplitude of this change in the total terrestrial water storage are revealed. Resolving changes in groundwater storage specifically from GRACE data is hindered by uncertainty in simulated soil moisture data.
This study tests the ability of five commonly used GRACE satellite datasets to measure a large...
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