Remote sensing reconstruction of long-term water level and storage variations of a poorly-gauged river in the Tibetan Plateau

The upper Brahmaputra River, China. The long-term water level and storage variations of the upper Brahmaputra River (UBR) are not yet clear due to the low accessibility of gauged data in high-altitude and harsh environments. The main objective of this study is to facilitate investigations of long-term river water level and storage variations over the UBR. Here we developed a hypsometric method to reconstruct temporally resolved long-term river water level observations based on remote sensing-derived accumulative water inundation area information and short-term altimetric water level data at 24 virtual stations (VSs) of the UBR. We further analyzed the intra-annual and inter-annual variations of the water level (storage) changes of the studied river reaches. The results reveal that the reconstructed water levels of the UBR are quite consistent with the water levels from the Hydroweb with an average R2 of 0.79 and the reconstructed water levels are generally consistent with the variation of the gauged runoff. The ascending amplitudes of the annual water level cycle of VSs were observed from upstream to downstream of the UBR, varying from 0.58 m to 6.92 m. Additionally, we find that the seasonal change in river water storage approximately accounted for one-tenth of the net mass seasonal amplitude of the UBR basin, as revealed from the Gravity Recovery and Climate Experiment (GRACE) data.