Estimating Water Storage Variations In Qaidam Basin Using GRACE Data

The Gravity and Climate Experiment(GRACE), launched in March 2002, is the second Gravisat in the world. The gravity variations that can be detected by GRACE include: changes due to surface and deep currents in the ocean, runoff and subsurface runoff, variations of mass within the earth, and exchanges between ice sheets or glaciers and the oceans. As a late-model remote sensing instrument with high precision, GRACE raises possibilities for new ways of estimating changes in terrestrial water storage. Qaidam Basin is a closed interior basin with vast area where the monitoring of groundwater and surface water is lack of coverage at present. Thus how to establish a comprehensive understanding of the water storage and its distribution in Qaidam Basin has become a problem. We are trying to solve this problem by virtue of GRACE data.Detailed information about GRACE mission and its data products are introduced, so is the rationale for inversion of water storage variations. Furthermore, the relevant issues of data selection and processing method are explored. In the present study, RL05 Level-2 GSM data provided by GFZ is chosen for calculation after preprocessing, anomaly-obtaining, decorrelation and spatial averaging. Influence of correlated error and truncation error is removed as much as possible during the data processing. All the calculations and data processing are implemented by MATLAB.The mass anomalies from 2003 to 2011 in Qaidam Basin are calculated and the result indicates a rising trend in water storage with a growth rate of ~0.27 mm/month and an intercept difference of ~29.46 mm. Anomaly sequence, represented as a curve in graphs, shows obvious seasonal characteristics. The estimation is validated with precipitation, actual evapotranspiration and other auxiliary data according to the principle of water balance. Both of the precipitation and actual evapotranspiration in Qaidam Basin increase in wave during the study period and accumulation of the former is higher which leads to the increase in water storage. Snowmelt and precipitation are the major recharge sources of the plain area. The contribution of snowmelt to total recharge can be neglected from May to October every year when precipitation is two order bigger in magnitude, which comes to 10-20% in other months. Each part of the basin has an increase in water storage from 2003 to 2011 and the increasing center is located in the southwest. Signal of water storage variations in western and southwestern part is able to affect the whole basin. Amplification of water storage decreases gradually from west to east and from southwest to northeast. Further research and demonstration ought to be developed with respect to distribution characteristics and evolution of the variations due to data limitation.