The use of GRACE data to monitor natural and anthropogenic induced variations in water availability across Africa

Inter-annual trends in terrestrial water storage (TWS) were extracted from monthly (01/2003-09/2012) Gravity Recovery and Climate Experiment (GRACE) data acquired over Africa and correlated (in a geographic information system [GIS] environment) with relevant temporal remote sensing, geologic, and hydrologic datasets. Findings include the following: (1) large sectors of Africa are undergoing statistically significant TWS variations (+44 mm/yr to -15 mm/yr) due to natural and anthropogenic causes; (2) warming of the tropical Atlantic Ocean apparently intensified Atlantic monsoons and increased precipitation and TWS over western and central Africa; (3) warming in the central Indian Ocean decreased precipitation and TWS over eastern Africa; (4) the high frequency of flooding events increased TWS over the Zambezi and Okavango basins; (5) extraction of fossil groundwater decreased TWS over the Saharan aquifers; (6) deforestation decreased TWS in three subbasins (Ubangi, Congo, and Sangha) of the Congo River Basin; and (7) the construction of dams increased TWS in the Blue Nile and Atbara subbasins. Given the 10 years of monthly GRACE data acquired on the subbasin scale across the globe, as well as the plans underway for deployment of a GRACE-FO and GRACE-II, using GRACE-derived TWS data should be considered an alternative, viable index for measuring temporal and spatial variations in water availability. (C) 2014 Elsevier B.V. All rights reserved.