Using satellite rainfall data to estimate direct flow

The main objective of this paper is to develop methodology for obtaining basin hydrological data for the Blue Nile sub-basins; as well to establish different types of data bank for the Blue Nile River Basin (BNRB). Data scarcity has been regarded as a huge problem in modeling the water resources of the Blue Nile River Basin. Satellite rainfall data together with the evapotranspiration have been used to calculate the runoff data. However, in data-scarce regions such as in a transboundary basin, remote sensing data could be a valuable option for hydrological predictions when ground rainfall stations are not available; as well as the remote sensing data can be used to fill gaps in the ground rainfall stations. The satellite rainfall data for all Blue Nile sub-basins were downloaded in a monthly basis for the period 1980-2010 from the Global Weather Data for the National Centres for Environmental Prediction (NCEP) from its website (www.globalweather.tamu.edu). This data were modified with the actual measured rainfall from near gauge stations for the period 1993-1999 by using a weighting factor depending on the distance between satellite data, by using inverse equation and the distances between the middle of sub-basins and the first and second nearest measured rainfall stations, respectively, the modified satellite rainfall data have been found. The selection of the boundary coordinates is used for each sub-basin to set the nearest rainfall satellite station in the middle of each sub-basin and, this is done by using the global weather and Google earth capability. The relation between modified rainfall data and the satellite rainfall data has been found. Different types of input data are used in the WEAP model after being modified and calibrated, such as satellite rainfall data, ET ref, effective precipitation, and crop coefficient K-c in the upper Blue Nile basin. The study area has been divided into 16 sub-basins. WEAP model has been applied to the whole Blue Nile basin, keeping the monthly values of K c same among the different sub-basins for the whole simulated period of 1980-2010. The observed stream flows, using rainfall-runoff relationship, have been simulated with the measured flows by using WEAP model at the four river gauging stations (El-deim, Giwiasi, Hawata and Khartoum) in a monthly time step yielded reasonable values. By evaluating the Blue Nile River Basin at the calibration period (1980-1995) in a monthly time step, the NSE, r(2), and d results for the Blue Nile River at the gauging stations showed a very good model performance.