Reconstruction of continuous GRACE/GRACE-FO terrestrial water storage anomalies based on time series decomposition

• We propose a simple and robust method for reconstructing continuous GRACE-like TWSA. • Reconstructed data using piecewise trends is better in capturing anomalous change. • Reconstructed TWSA detects the Australian drought during the data gaps in 2018. Since 2002, the terrestrial water storage anomalies (TWSA) derived from the Gravity Recovery and Climate Experiment (GRACE) and its successor, GRACE Follow-on (GRACE-FO), have been widely used in water resources management , drought monitoring and forecasting. However, the disrupted TWSA time series due to the temporal gap (i.e., from July 2017 to May 2018) between the two missions limits its further applications. To bridge this gap, we reconstruct the TWSA by combining the TWSA trends from the GRACE/GRACE-FO TWSA data (including the long-term trend and piecewise trends) with the de-trended TWSA of Humphrey and Gudmundsson's datasets for the period from April 2002 to July 2019 over Australia. These reconstructed data are evaluated against the TWSA from GRACE/GRACE-FO, a water balance model, and three recently published reconstructed products. Results suggest that our reconstructed TWSA based on the piecewise trends shows great consistency with GRACE/GRACE-FO comparing to other reconstructed products with a correlation coefficient (R) of 0.98, root-mean-square error (RMSE) of 0.70 cm, and Nash-Sutcliffe efficiency (NSE) of 0.96. The proposed reconstruction approach presented in the current study is straightforward and efficient to enable a seamless continuation of the TWSA time series between the GRACE and GRACE-FO missions in regional and global hydrological studies.