The estimation of water storage change and land subsidence induced by the Bakun Dam, Malaysia, using GRACE, Landsat, and GPS data

The Bakun Dam located in Sarawak Malaysia is the largest hydropower dam in Southeast Asia. The dam commenced its operation in 2010 causing a vast extent of the freshwater reservoir, changing the characteristic of Sarawak's rainforest and the natural flow of the regional river networks. The relocation of the water storage affects the natural hydrological cycle and leads to large-scale land subsidence over the area. This study, for the first time, quantifies the terrestrial water storage variation (ΔTWS) and land subsidence induced by the Bakun Dam using multiple satellite observations (GRACE, Landsat), land surface models (CABLE, GLDAS, NCEP, ECMWF), and ground observations (GPS). During the impoundment period, GRACE observes the increased ΔTWS estimate of the Bakun Lake by approximately 200 mm and Landsat detects the increased lake extent by around 600 km². The increased ΔTWS and lake area estimates are corresponding to approximately 130 m surplus lake level derived by the forward models. In contrast to GRACE, the land surface models cannot capture the increased ΔTWS due to the incomplete water storage components used in the TWS simulation. The Bakun Dam induced surface displacement is determined using the disk load model associated with the GRACE-derived lake level and Landsat-derived lake extent. The commencement stage of the Bakun Dam induces the large-scale land subsidence, which causes the Earth's surface at the GPS-BIN1 station to subside by 10 mm, and moves toward the Bakun Lake by 5 mm. Computing the surface displacements directly from GRACE spherical harmonic coefficient data fails to capture the subsidence feature, mainly due to the truncation error. Incorporating GRACE with other remote sensing data allows the exploitation of the gravity signal at a much smaller spatial scale than its intrinsic resolution as demonstrated in this study.