Optimal areal rainfall estimation over Lake Victoria using rain gauges and satellite data.

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University of Dar es Salaam
The main goal of this study is to model the spatial variation of rainfall in the Lake Victoria catchment and use the calibrated model to estimate average rainfall over the lake. Two methods of estimation of rainfall are presented. The whole Lake area was divided into grids of spatial resolution 7.6 km by 7.6 km. Geostatistical interpolation methods (kriging) were used to estimate rainfall for each grid square by taking weighted averages of irregularly observed rainfall. The geostatistical interpolation techniques implemented are Ordinary Kriging (OK), Kriging With External Drift (KED), Ordinary Kriging of the Rainfall-CCD ratio and Cokriging (COK). Variogram models were used to model the spatial variation of rainfall. The estimates are based on measurements of dekadal rainfall in 105 raingauge stations. The OK gave an R2 of 51 %. The kriging method was improved by using the cold cloud duration (CCD) data as implemented in KED. The R2 of KED was 62 % and that of the ratio kriging was 50 %. The COK produced unstable results and was not implemented. The second method of estimation was based on measurements of both dekadal rainfall and cold cloud duration (CCD. This method known as the TAMSAT method is based on the regression rainfall and CCD. The regression models were then used to transform CCD into rainfall. The TAMSAT method seems to reproduce the rainfall over the lake better than the kriging methods. Kriging with external drift was found to be the best of the kriging algorithms used. A linear relationship was then derived between the lake surface and land catchment rainfall. The lake rainfall estimate over the lake using TAMSAT method was compared with previous water balance estimates by Piper et al. (1986) and the correlation is good.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS EAF QC926.T34K37)
Rainfall reliability, Rain gauges, Lake Victoria, Tanzania
Kassoh, F. (2001). Optimal areal rainfall estimation over Lake Victoria using rain gauges and satellite data. Master dissertation, University of Dar es Salaam.