The troposphere a ects electromagnetic signal propagation causing signal path bendingrnand the alteration of the electromagnetic wave velocity. Tropospheric delay can introducerna considerable error in satellite positioning if it is not properly estimated. The averagernGPS signal delay in the zenith direction can vary from 1.8 m to 2.5 m depending onrnmeteorological conditions and site location. In this work, the spatial and temporalrnvariations of the zenith tropospheric delay (ZTD), zenith wet delay (ZWD) and precipitablernwater(PW) over Ethiopia, are analyzed using ECMWF (European Centre for Medium-rnRange Weather Forecast) ERA-interim pressure-level atmospheric data and comparedrnwith ZTD time series for 5-year period from 2007-2011 measured at several GPS stationsrnfrom the Crustal Movement Observation Network of over Great Rift Valley regions ofrnEastern Africa which are managed by UNAVCO (University NAVstar COnsortium).rnA modi ed version of tropospheric delay correction model, SHAO-C used in China,rnis assessed for its performance over Ethiopia. ZTD is modeled directly by a cosinernfunction together with an initial value and an amplitude at a reference height in eachrngrid, and the variation of ZTD along altitude, latitude and longitude is tted with arnsecond order polynomials. The coe cients of the modi ed SHAO-C are generated usingrnthe ECMWF ERA-Interim data at 0.75x0.75 degree latitude-longitude grid, featuringrnregional characteristics in order to facilitate a wide range of navigation and other surveyingrnapplications. The altitude is obtained from high resolution Digital Elevation Modelrn(DEM). The overall average bias ranges between -4.3 cm to -1 cm for ZTD, -3.42 cmrnto -0.584 cm for ZWD and -1.12 cm to -0.34 cm for PW, and the RMSE is less than 4.5rncm. The results are assessed for ful lling the requirements of most GNSS navigation orrnpositioning applications in terms of the tropospheric delay correction