Improvement of Precipitation Estimation Techniques over the Nile Basin

Abstract

The Nile Forecast System (NFS) is a hydro-meteorological forecasting system developed in 1992. The NFS rainfall estimation algorithm is based on the Cold Cloud Duration (CCD) technique which depends on the thermal Infrared (IR) 10.8μm band. This algorithm was improved in 2009 to take advantage of the METEOSAT Second Generation (MSG) satellite which provides more IR bands. The Improved NFS algorithm uses the multi-spectral IR technique which depends on the CCD and the brightness indices of other IR bands (9.7, 12.0, and 13.4μm). In this study, the accuracy of the CCD technique is evaluated for a 10 years (1998-2010) continuous stream of real-time satellite data through comparison with the gridded raingauge data sets (Obs). The results showed that METEOSAT Satellite Rainfall Estimates (MSRE) rainfall estimates are overestimated in all sub-basins except the Blue Nile basin, and White Nile between Malakal and Mogren, where it is underestimated. It is also shown that the largest deviations occur during the peak season, where the CCD techniques did not represent the rainy seasons over the sub-basins adequately.