Abstract:

Despite the gravity recovery and climate experiment (GRACE) and GRACE follow-on (GRACE-FO) satellites provide a new capability for retrieving and monitoring of global large-scale groundwater storage anomaly (GWSA), its data products struggle to provide access to small-scale GWSA information with high spatial resolution. In this paper, a dynamic downscaling method was employed to improve the spatial resolution of GWSA data retrieved by GRACE/GRACE-FO and to analyse the spatio-temporal distribution of GWSA in the eastern area of Korla, Xinjiang, China. Firstly, a GWSA numerical model of eastern region of Korla was constructed and optimized based on data fusion for purposes of the spatial downscaling conversion. Then, the resolution of GRACE/GRACE-FO-derived GWSA data was downscaled from 1° to 0.25° and 0.05° via the optimized model. The derived GWSA results were further compared with the well-monitored groundwater level (GWL) data. Finally, the GWSA trends in specific study areas were evaluated using 0.05° GWSA data. Specific results include: ①Compared to the 1° GWSA without downscaling transformation, the high-resolution GWSA data after downscaling are spatially smoother and more detailed, whose correlation with the GWL monitoring data is increased, indicating an improvement in inversion accuracy and reliability. ②At small scales, the downscaled GWSA can reflect the groundwater regime, such as seasonal and interannual variations, as well as long-term depletion, in specific water sources. ③The GWSA in the eastern area of Korla states the characteristics of spatial and temporal differences, whose trends from 2005 to 2020 are -1~1 mm·a^-1, generally following an increasing tendency in the south and a decreasing tendency in the north. Specifically, the GWSA slopes in the southern and northern mountainous zones are greater than those in the relatively flat central region.

Key words: GRACE, groundwater storage anomaly, dynamic downscaling, groundwater model, data fusion