The Nile basin River system spans 3 million km2 distributed over ten nations. The eight upstream riparian nations, Ethiopia, Eretria, Uganda, Rwanda, Burundi, Congo, Tanzania and Kenya are the source of approximately 86% of the water inputs to the Nile, while the two downstream riparian countries Sudan and Egypt, presently rely on the river's flow for most of the their needs. Both climate and agriculture contribute to the complicated nature of Nile River management: precipitation in the headwaters regions of Ethiopia and Lake Victoria is variable on a seasonal and inter-annual basis, while demand for irrigation water in the arid downstream region is consistently high. The Nile is, perhaps, one of the most difficult trans-boundary water issue in the world1, and this study would be the first initiative to combine NASA satellite observations with the hydrologic models study the overall water balance in a comprehensive manner. The cornerstone application of NASA's Earth Science Research Results under this project are the NASA Land Data Assimilation System (LDAS)2 and the USDA Atmosphere-Land Exchange Inverse (ALEXI)3 model. The end-users such as Regional Center for Mapping of Resources for Development (RCMRD, Nairobi, Kenya), Eastern Nile Technical Regional Office (ENTRO, Addis Ababa, Ethiopia), Ethiopian and Kenya Meteorological and Famine Early Warning System Network (FEWSNet) will be the eventual benefactors of this work.