Water budget closure based on GRACE measurements and reconstructed evapotranspiration using GLDAS and water use data for two large densely-populated mid-latitude basins

The GRACE-derived terrestrial water storage change (TWSC) provides an unprecedented opportunity to close the terrestrial water budget. However, it remains challenging to achieve the balance without the consideration of human water use (e.g., irrigation and inter-basin water diversion) for the estimation of other water budget terms such as the evapotranspiration. In this study, the terrestrial water budget closure is tested over the Yellow River Basin (YRB) and Changjiang River Basin (CJB, also called Yangtze River Basin) of China. First, the evapotranspiration is reconstructed using the GLDAS-1 land surface models, the high quality observation-based precipitation, naturalized streamflow, and the irrigation water (hereafter, ETrecon). The ETrecon, evaluated using the mean annual water-balance equation, is of good quality with the absolute relative errors less than 1.9%. The total basin discharge (Rtotal) is calculated as the residual of the water budget among the observation-based precipitation, ETrecon, and the GRACE-TWSC. The difference between Rtotal and the observed total basin discharge is used to evaluate the budget closure, with the consideration of inter-basin water diversion. After the ET reconstruction, the mean absolute imbalance value reduced from 3.31 cm/year to 1.69 cm/year and from 15.40 cm/year to 1.96 cm/year over the YRB and CJB, respectively. The estimation-to-observation ratios of total basin discharge improved from 180.8% to 86.8% over the YRB, and from 67.0% to 101.1% over the CJB. The yearly timescale is the finest temporal scale for the analysis in this study due to the data limitation of naturalized streamflow, irrigation water, and water diversion. The proposed ET reconstruction method is applicable to other human-managed river basins to provide an alternative estimation.