Deformation Monitoring And Simulation Of Surface Load On The North China Plain GRACE Satellite Gravity

Water resource is the basis of producing and living in man’s society, and also maintains the balance of natural environment. The development and utilization of water resources restricts the development of North China Plain (NCP). Because of excessive exploitation of groundwater resources, NCP is the one of the serious area in the world for its land subsidence. Temporal variations in the geographic distribution of surface mass (continental water, ocean mass and atmospheric mass) cause a deformation of the Earth’s surface. Calculating the loading deformation can explain the natural deformation phenomenon under subsiding background, and presents a new sight into the dynamics of land subsidence. Traditional deformation observation has space limitations. This research based on geophysical theory, combining GRACE data and ANN to explore the method of deformation inversion, and explored hydrological loading deformation in NCP. Specific contents as follows:(1) Using GARCE and ANN to simulate loading deformation. Deformations in NCP from January2009to December2010are simulated. The posterior-variance-test shows a good fitness between the simulated and observed value, with C<0.5, P>0.8, average RMSE is0.501mm and R2=0.742. The influence of various parts of the TWSC, including ground water storage change (GWSC) and soil water storage change (SWSC), is also investigated by changing the water storage input of ANN. The results indicate that:(1) the results showd the best fitness when select TWSC as the input of ANN;(2) the GWSC has more impact on loading deformation than SWSC in NCP.(2) Using GRACE dimensionless coefficients to calculate loading deformation. Deformations in China are calculated and compared with deformation observed by27GPS sites located in the same region for reliability validation. The comparison shows good agreements between the displacements estimated from GPS and GRACE, and litter station existed deviation. Correlation coefficients r and RMSE computed for monthly time series of27stations, the results indicate that:about26%of correlation coefficient larger than0.5,60%of correlation coefficient between0and0.5, and14%show negative correlation. The average RMSE is6.2mm, the average RMSE of south area is5.2mm and north is6.7mm. GRACE is highly sensitive to large-scale mass variability which is not appropriate to explore small-scale water storage changes such as basin.(3) Calculating Climate-driven hydrological loading deformation in NCP. This paper explored the seasonal variations and secular variations in NCP. The results indicate that:both water storage and deformation has obvious seasonal change, and changes of water storage were contrary to the loading deformation. In addition, soil water change was contrary to the ground water change in the same period because of seasonal inconsistent. Secular deformation results shows that reason of loading deformation in NCP include two factors: ground water loading and soil water loading. Ground water exploitation reduced loading deformation to some extent. Therefor, in the high-level exploitation area, we should pay more attention to the loading deformation caused by GWS.