Global analysis of spatiotemporal variability in merged total water storage changes using multiple GRACE products and global hydrological models

International audienceProliferation of different total water storage (TWS) change products from the Gravity Recovery and Climate Experiment(GRACE) satellites, including the newly released mascon solution, warrants detailed analysis of theiruncertainties and an urgent need to optimize different products for obtaining an elevated understanding ofTWS changes globally. The three cornered hat method is used to quantify uncertainties in TWS changes fromGRACE observations, land surface models, and global hydrological models, indicating that the WaterGap GlobalHydrological Model (WGHM)-based TWS changes show the lowest uncertainty over sixty basins covering arange of climate settings and levels of human activities globally. Bayesian model averaging (BMA) usingWGHM TWS output for training (2003–2006) is subsequently used to merge TWS changes from variousGRACE products. Results indicate that the BMA-based TWS changes show the highest consistency with theWGHM output for the validation period (2007–2009) in terms of the highest medium of the Nash-Sutcliffe Efficiency(NSE) coefficient of 0.714 among allTWS change products for the sixty basins. The mascon solution showsa mediumof NSE of 0.682, higher than other GRACETWS change products. Analysis of spatiotemporal variabilityin BMA-basedTWS changes and the mascon solution indicates that higher depletion rates for the 13-year period(Apr 2002–Mar 2015) occurred over major aquifers due to groundwater withdrawals for irrigation (e.g., Tigris,Central Valley, Ganges, upper Arkansas, and Indus), basins subject to great glacier and snow melting (e.g.,Yukon, Fraser, and eastern Ganges), the north Caspian Sea (e.g., Don and Ural), and the Caspian Sea. Significantincreasing trends in TWS are found over west (e.g., Gambia and Niger) and South Africa (e.g., Zambezi), SouthAmerica (e.g., Essequibo), North America (e.g., Koksoak and Missouri), central India (e.g., Narmada and Godavari),the north Tibetan Plateau, and the middle Yangtze River basin. Empirical Orthogonal Function decompositionis used to investigate spatiotemporal variations in the GRACE mascon solution-based TWS changes during thestudy period, showing a detailed pattern of increasing and decreasing long-termtrends, interannual and seasonalvariations in TWS over the global land surface