Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 21, 4533-4549, 2017
https://doi.org/10.5194/hess-21-4533-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
12 Sep 2017
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, University College London, London, UK
2Department of Geography, University College London, London, UK
3Centre for Geography, Environment and Society, University of Exeter, Exeter, UK
4CNRS – UMR 6118 Géosciences Rennes, Université de Rennes 1, Rennes, France
5Department of Geology & Petroleum Studies, Makerere University, Kampala, Uganda
6Directorate of Water Resources Management, Ministry of Water & Environment, Entebbe, 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 TWS into individual terrestrial water stores (e.g. groundwater storage). Here, we test the phase and amplitude of three GRACE ΔTWS signals from five 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) in two sub-basins (LVB: Lake Victoria Basin; LKB: Lake Kyoga Basin) of the Upper Nile Basin. The analysis extends from January 2003 to December 2012, but focuses on a large and accurately observed reduction in ΔTWS of 83 km3 from 2003 to 2006 in the Lake Victoria Basin. We reveal substantial variability in current GRACE products to quantify the reduction of ΔTWS in Lake Victoria that ranges from 80 km3 (JPL-Mascons) to 69 and 31 km3 for GRGS and GRCTellus respectively. Representation of the phase in TWS 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 90, 84, and 75 % of the variance respectively in "in situ" or "bottom-up" ΔTWS in the LVB. Resolution of changes in groundwater storage (ΔGWS) from GRACE ΔTWS is greatly constrained by both uncertainty in changes in soil-moisture storage (ΔSMS) modelled by GLDAS LSMs (CLM, NOAH, VIC) and the low annual amplitudes in ΔGWS (e.g. 1.8–4.9 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; this uncertainty is disregarded in analyses of ΔTWS and individual stores applying a single GRACE product.

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., 21, 4533-4549, https://doi.org/10.5194/hess-21-4533-2017, 2017.
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This study tests the phase and amplitude of GRACE TWS signals in the Upper Nile Basin from five commonly used gridded products (NASA's GRCTellus: CSR, JPL, GFZ; JPL-Mascons; GRGS) using in situ data and soil moisture from the Global Land Data Assimilation System. Resolution of changes in groundwater storage (ΔGWS) from GRACE is greatly constrained by the uncertain simulated soil moisture storage and the low amplitude in ΔGWS observed in deeply weathered crystalline rocks in the Upper Nile Basin.
This study tests the phase and amplitude of GRACE TWS signals in the Upper Nile Basin from five...
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