This thesis studies the movement of GPS (IGS) stations due to elastic surface deformation ofrnthe earth caused by hydrological water loading as detected by the combined monthly GravityrnRecovery and Climate Experiment (GRACE) and GPS data for a period of five years fromrnJune 2008 to March 2012. The GRACE data was obtained from four different data processingrninstitutes which are Geoforschungszentrum (GFZ) Potsdam, Centre for Space Researchrn(CSR) Texas, NASA Jet propulsion Laboratory (JPL) and Centre National dâ€™Etudes Spatialesrn(CNES) to estimate total water storage anomalies over the whole of East African region as arncase study involving Tanzania, Kenya, Uganda, Rwanda, Burundi and Ethiopia. Five IGSrnstations were used in this study in addition to six stabilization IGS sites in order to strengthenrnthe network and get improved deformation estimates. Using 650 km half radius Gaussianrnsmoothing, GRACE detected about 5 mm to 17 mm peak-to-peak of total water storagernsignal with maximum of 7.3 mm in May 2010 and minimum of ~ -17 mm in July 2011 withrn2.88 cm mean standard deviation from the mean of the four standard deviations of the fourrnGRACE data models. The derived water load estimates from GRACE were compared withrn3D deformation estimates from GPS observations and found good agreement in areas withrnhigh and low hydrological signals at every GPS point with maximum correlation of 0.8 forrnhorizontal and vertical components shown by MAL2 and RCMN stations considering enoughrndata between the two signals being correlated. The monthly station positions were obtainedrnwith good repeatability computed as weighted root mean square of ~0 mm to 4 mm forrnhorizontal component and ~3 mm to ~10 mm for vertical component. NKLG showed thernlargest repeatability of 4.6 mm and 18.4 mm for east component and vertical componentrnrespectively. The annual GPS signal for north and east components ranged from 1 mm to 4rnmm and ~5 mm to ~9 mm for vertical component. However, ADIS and MBAR stationsrnshowed strong negative correlation with GRACE signal in north components while RCMNrnand MAL2 showed strong negative correlations in east components compared with other IGSrnstations. The analysis of the combined results revealed strong coincidence between GRACErnand GPS signal on water loading effect to all studied IGS stations in the study area. Thernagreement was also observed when GARCE monthly solution signal from this study wererncompared with precipitation, rainfall and river water discharge from previous studies.rnKey words: GRACE, GPS, hydrological water loading, IGS station movements