Satellite based water balance of the Nile River basin a multisensor approach

Satellite-informed estimates of distributed hydrologic fluxes and storages in remote, ungauged, or contentious river basins is the subject of active research. Here we review recent developments in remotely sensed water flux and balance estimates for large basins, including the Nile River basin, and present results of a new analysis that applies TRMM, GRACE, and a Meteosat-based implementation of the ALEXI evapotranspiration algorithm to generate spatially and temporally distributed estimates of hydrologic fluxes and storages in the Nile basin. Results are evaluated using previous studies of the Nile water balance, historic river gauge data, and available in situ measurements of distributed fluxes. It is found that the independent estimates of precipitation, water storage changes, and evapotranspiration offered by TRMM, GRACE, and ALEXI, respectively, can be used to close the climatological water balance of the Nile River basin and critical Nile subbasins to first order, but that the technique has limitations at shorter time scales due to random error, at smaller spatial scales, due to resolution limitations, and in the characterization of systematic error due to limited availability of relevant in situ observations. The strengths and limitations of the analysis will be evaluated with respect to alternative methodologies and to resource information needs in the Nile basin