Spatiotemporal Variation and Driving Analysis of Groundwater in the Tibetan Plateau Based on GRACE Downscaling Data

The special geographical environment of the Tibetan Plateau makes ground observation of Ground Water Storage (GWS) changes difficult, and the data obtained from the GRACE gravity satellites can effectively solve this problem. However, it is difficult to investigate the detailed GWS changes because of the coarser spatial resolution of GRACE data. In this paper, we constructed a 0.1 degrees resolution groundwater storage anomalies (GWSA) dataset on the Tibetan Plateau from 2002 to 2020 based on a phased statistical downscaling model and analyzed the spatiotemporal variation and driving factors of the GWSA in order to better study the changes of GWS on the Qinghai Tibet Plateau. The results show that: (1) In the Tibetan Plateau and 12 sub-basins, the GWSA before and after downscaling show a very high correlation in time series and relatively good performance in spatial consistency, and the downscaled GWSA indicate a consistent trend with the measured groundwater level. (2) The GWSA on the Tibetan Plateau shows a downward trend (-0.45 mm/yr) from 2002 to 2020, and the variation trend of the GWSA in the Tibetan Plateau shows significant spatial heterogeneity. (3) The GWSA changes in the Tibetan Plateau are mainly dominated by natural factors, but the influence of human activities in individual sub-basins can not be ignored. Among the teleconnection factors, El Nino-Southern Oscillation Index (ENSO) has the greatest influence on the GWSA on the Tibetan Plateau.