THE USE OF GRACE AND TRMM DATA TO QUANTIFY THE SPATIAL AND TEMPORAL VARIATIONS IN PRECIPITATION AND TERRESTRIAL WATER STORAGE (TWS) ACROSS THE NILE RIVER BASIN

Inter-annual trends in terrestrial water storage (TWS) were extracted from monthly Gravity Recovery and Climate Experiment (GRACE) data acquired (04/2002 to 08/2011) over the Nile River Basin (NRB) and correlated (in a GIS environment) with the inter-annual trends extracted from TRMM data that span the same time period and with other relevant temporal remote sensing, geologic, hydrologic, climatic, and topographic datasets. Findings include the following: (1) large sectors of the NRB are undergoing statistically significant variations (+7 mm/yr to –10 mm/yr) in TWS due to climate change and man-made interventions; (2) warming in the central Indian Ocean decreased precipitation (-5.5 mm/yr ) and TWS over eastern (-11.5 mm/yr) and southern Africa (-3.5 mm/yr); (3) the construction of dams (e.g., Merowe High Dam, Tekezé, Amerti-Neshi, Beles, Gilgel Gibe I, Gilgel Gibe II, and Karadobi) throughout the GRACE period increased TWS (6.5 mm/yr) in upstream Nile Valley countries despite the decrease (-6.5 mm/yr) in precipitation. Given the 10-year monthly GRACE record of water availability data (represented by GRACE TWS) acquired on the sub-basin scale across the globe, and the plans underway for the deployment of a GRACE follow-up (2016–2026), consideration should be given to using GRACE TWS data as an alternative, viable index for monitoring the impact of climate change and human interventions on hydrologic systems on local, regional, and continental scales.