Measuring Terrestrial Water Storage Change Using GRACE, GPS and Absolute Gravity Data in Scandinavia

Gravity satellite GRACE-derived terrestrial water storage change would be seriously affected by glacial isostatic adjustment(GIA) in Scandinavia. To solve this problem, it is calculated that the measured linear ratio of GIA gravity rates and vertical displacement rates according to the data from collocation stations for absolute gravity and GPS. Using the linear ratio and uplift field derived from GPS observation network, the gravity signal of GIA is got. Gravity change rates from GRACE RL05 data can be corrected for GIA using independent gravity rates derived from GPS vertical velocities, and then it is calculated that corresponding equivalent water thickness in Scandinavia and the uncertainties are evaluated by considering the uncertainties from data. The proposed method utilizes observational data only and can avoid the enormous uncertainty from GIA models.The results are compared with that of two hydrological models. The ratio of gravity versus uplift obtained by ground-based measurements in Scandinavia is 0.148&#177;0.020 <i>μ</i>Gal/mm(1 Gal=10^-2 m/s²), which validates Wahr's approximate theoretical ratio and is very close to the result from North America. From January 2003 to March 2011, terrestrial water storage shows obvious increase in Scandinavia. The main signal locates at the V&#228;nern lake which is in the southern tip of the peninsula. The rate of total water storage is 4.6&#177;2.1 km³/a and the corresponding cumulative quantity is 38&#177;17 km³ for the period 2003 to 2011. Results from hydrological models are consistent with the result very well. The correlation coefficient between GRACE and WGHM hydrological model can reach 0.69, while for GLDAS model the correlation coefficient is slightly smaller