Spatial distribution characteristics and mechanism of nonhydrological time-variable gravity in China's Mainland

The purpose of this study is to explore nonhydrological mass transfer in China's Mainland.For this purpose,gravity recovery and climate experiment(GRACE)data were obtained to study the spatial distribution of time variant gravity signals in China's Mainland.Then,from auxiliary hydrological data processed according to the current hydrological model,a new more comprehensive hydrological model of China's Mainland was constructed.Finally,the time variant signals of this new hydrological model were removed from the time variant gravity field computed from GRACE data,thus obtaining a description of the nonhydrological mass transfer of China's Mainland.The physical sources and mechanisms of the resulting mass transfer are then discussed.The improved,more realistic,hydrological model used here was created by selecting the hydrological components with the best correlations in existing hydrological models,by use of correlation calculation,analysis,and comparison.This improved model includes water in soils and deeper strata,in the vegetation canopy,in lakes,snow,and glaciers,and in other water components(mainly reservoir storage,swamps,and rivers).The spatial distribution of the transfer signals due to nonhydrological mass in China's Mainland was obtained by subtracting the combined hydrological model from the GRACE time-variable gravity field.The results show that the nonhydrological signals in China's Mainland collected in GRACE data were mainly positive signals,and were distributed in the Bohai Rim and the northern and eastern parts of the Tibetan Plateau.The above nonhydrological mass transfer signals have been studied further and are discussed.The results show that the nonhydrological mass migration signals in the Bohai Rim region originate primarily from sea level change and marine sediment accumulation.The mass accumulation from Indian plate collision in the Tibetan Plateau appears to be the main reason for the increase in the residual gravity field in that region.

Runoff variations in the Yangtze River Basin and sub-basins based on GRACE, hydrological models, and in-situ data

Water budget closure is a method used to study the balance of basin water storage and the dynamics of relevant hydrological components(e.g.,precipitation,evapotranspiration,and runoff).When water budget closure is connected with terrestrial water storage change(TWSC)estimated from Gravity Recovery and Climate Experiment(GRACE)data,variations in basin runoff can be understood comprehensively.In this study,total runoff variations in the Yangtze River Basin(YRB)and its sub-basins are examined in detail based on the water budget closure equation.We compare and combine mainstream precipitation and evapotranspiration models to determine the best estimate of precipitation minus evapotranspiration.In addition,we consider human water consumption,which has been neglected in earlier studies,and discuss its impact.To evaluate the effectiveness and accuracy of the combined hydrological models in estimating subsurface runoff,we collect discharge variations derived from in situ observations in the YRB and its sub-basins and compare these data with the models’final estimated runoff variations.The estimated runoff variations suggest that runoff over the YRB has been increasing,especially in the lower sub-basins and in the post-monsoon season,and is accompanied by apparent terrestrial water loss.