Abstract:This study proposes a new method for predicting surface deformation caused during GERD storage based on spherical harmonic transform. Firstly, it is assumed that the GERD reservoir is filled up during 5, 10 and 15 years respectively, and the area, volume and water level of the reservoir are obtained for each month of the storage process using SRTM-DEM data. The surface deformation caused by the corresponding storage process is calculated after spherical harmonic expansion and the accuracy of the results is increased by increasing the upper limit of the maximum harmonic degree. The estimated vertical displacement velocity induced for each of the three filling strategies are 11.8 mm/a, 5.9 mm/a and 3.9 mm/a, respectively. The induced east-west displacement velocity are 1.8 mm/a and 1.4 mm/a, 0.9 mm/a and 0.7 mm/a, 0.6 mm/a and 0.4 mm/a, respectively. The induced south-north displacement velocity are 2.6 mm/a and 4.4 mm/a, 1.3 mm/a and 2.2 mm/a, 0.8 mm/a and 1.5 mm/a, respectively.