As global warming continues,the monitoring of changes in terrestrial water storage becomes increasingly important since it plays a critical role in understanding global change and water resource management.In North America as elsewhere in the world,changes in water resources strongly impact agriculture and animal husbandry.From a combination of Gravity Recovery and Climate Experiment（GRACE） gravity and Global Positioning System（GPS） data,it is recently found that water storage from August,2002 to March,2011 recovered after the extreme Canadian Prairies drought between 1999 and 2005.In this paper,we use GRACE monthly gravity data of Release 5 to track the water storage change from August,2002 to June,2014.In Canadian Prairies and the Great Lakes areas,the total water storage is found to have increased during the last decade by a rate of 73.8 ± 14.5 Gt/a,which is larger than that found in the previous study due to the longer time span of GRACE observations used and the reduction of the leakage error.We also find a long term decrease of water storage at a rate of-12.0 ± 4.2 Gt/a in Ungava Peninsula,possibly due to permafrost degradation and less snow accumulation during the winter in the region.In addition,the effect of total mass gain in the surveyed area,on present-day sea level,amounts to-0.18 mm/a,and thus should be taken into account in studies of global sea level change.
Wang HanshengXiang LongweiJia LuluWu PatrickSteffen HolgerJiang LimingShen Qiang
We use the average crustal structure of the CRUST1.0 model for the Tibetan Plateau to establish a realistic earth model termed as TC1 P, and data from the Global Land Data Assimilation System(GLDAS) hydrology model and Gravity Recovery and Climate Experiment(GRACE) data, to generate the hydrology signals assumed in this study. Modeling of surface radial displacements and gravity variation is performed using both TC1 P and the global Preliminary Reference Earth Model(PREM). Furthermore, inversions of the hydrology signals based on simulated Global Positioning System(GPS) and GRACE data are performed using PREM. Results show that crust in TC1 P is harder and softer than that in PREM above and below a depth of 15 km, respectively, causing larger differences in the computed load Love numbers and loading Green’s functions. When annual hydrology signals are assumed,the differences of the radial displacements are found to be as large as approximately0.6 mm for the truncated degree of 180; while for hydrology-trend signals the differences are very small. When annual hydrology signals and the trends are assumed, the differences in the surface gravity variation are very small. It is considered that TC1 P can be used to efficiently remove the hydrological effects on the monitoring of crustal movement. It was also found that when PREM is used inappropriately, the inversion of the hydrology signals from simulated annual GPS signals can only recover approximately 88.0% of the annual hydrology signals for the truncated degree of 180, and the inversion of hydrology signals from the simulated trend GPS signals can recover approximately 92.5% for the truncated degree of 90. However, when using the simulated GRACE data, it is possible to recover almost 100%. Therefore, in future, the TC1 P model can be used in the inversions ofhydrology signals based on GPS network data. PREM is also valid for use with inversions of hydrology signals from GRACE data at resolutions of approximately 220 km and larger.
Wang HanshengXiang LongweiWu PatrickJia LuluJiang LimingShen QiangSteffen Holger
The long-term reclamation-induced ground subsidence in Macao, a coastal city of southern China was investigated. Persistent scatterer interferometry (PSI) technique was applied to retrieve the deformation rate in Macao during the period from April 2003 to August 2010 with a total of 41 scenes of descending ASAR data sets. The PSI-retrieved results show a relatively stable pattern in Macao Peninsula, Taipa Island and Coloane Island, with an average subsidence velocity of -3 mm/a. In contrast, relatively large subsidence rates are highlighted in Cotai area, a new reclamation land in 1990s, in which an average subsidence velocity is about -10 mm/a. A consistent relationship between the PSI results and the leveling measurements indicate that this PSI technique is an effective tool to monitor the reclamation-induced ground subsidence with a high accuracy and adequate spatial details. Accordingly, the valuable ground subsidence results generated by PSI can be used not only for early detection and remedial activities of potential settlement of building, but also for helping the local government to formulate regional sustainable development planning and decision-making in disaster prevention and mitigation.
