Reasearch On The Total Water Storage Change In The Yangtze River Basin And Its Connection With The Extreme Weather Events Using Time-variable Gravity Data

With the rapid development of human society,climate change has increasingly become the core issue of concern.More and more research shows that global climate events caused by the coupled system of the atmosphere and the ocean will have a significant impact on global climate change.As the largest basin in China and the third largest in the world,the Yangtze River Basin(YRB)is under the control of the southeast monsoon,southwest monsoon,and northeast monsoon,and is subject to the global meteorological events represented by El Nino-Southern Oscillation(ENSO).Recently,several extreme floods and droughts have occurred in the YRB,which have strong correlations with ENSO as well as the Indian Ocean Dipole(IOD),the Arctic Oscillation(AO)and the North Atlantic Oscillation(NAO)according to the study of hydroclimatic data.Analyzing the impact of these meteorological events will provide an important supplement to the study of extreme floods and droughts in the YRB.With the development of space technology,the new-generation satellite gravity plan represented by the Gravity Recovery and Climate Experiment(GRACE)provides high-quality,high-precision continuous observation data for the changes in terrestrial water storage.Combining the satellite gravity observation data and the meteorological indices,we can not only quantify the impact of different meteorological events but also have forward-looking scientific significance for disaster prevention and reduction in the YRB.In this paper,the total water storage change(TWSC)in the YRB was inverted using the GRACE monthly variable gravity field model series from July 2002 to June 2017 for a total of 15 years.The meteorological indices such as the ENSO index and the IOD index were combined with hydroclimatic data to comprehensively analyze the impact of the meteorological events on the abnormal changes in water storage in the YRB.The correlation between meteorological events and extreme floods and droughts in the YRB was revealed during the analysis and the impact caused by ENSO on the major river basins was also shown.The main work and contributions are listed below:1.Research on the GRACE time-varying gravity field data processing theory and method.Firstly,the method of using GRACE data to invert the change of surface quality was derived;Secondly,the GRACE post-processing method was deeply studied by comparing the spatial smoothing effects of Gaussian Filter,Fan Filter and decorrelation filter,and the optimal filter combination method which combined decorrelation filter with Fan Filter was proposed.Thirdly,the calculation methods of signal leakage correction using signal separation method,prior model method and scale factor method were introduced.2.Research on the Method for determining the continuous time series of TWSC anomaly(TWSA)in the YRB.Firstly,the reliability and data quality advantages of the filter combination method are verified taking GRACE Level-3 product results as a reference;Secondly,the SSAM interpolation method based on Singular Spectrum Analysis(SSA)were determined as the optimal interpolation method for the missing data after being compared to several common interpolation methods;Thirdly,the combination of SSA and least square fitting which could effectively separate and extract the trend signal and seasonal signal was determined as the optimal elimination method of trend and seasonal signal.3.The effect of ENSO on the TWSA in the YRB was found obvious using the cross-correlation analysis method.The correlation between ENSO and TWSA was calculated in the entire YRB,with the peak cross-correlation of 0.53 and a 6-month time lag.The cross-correlation peaks in the upper,middle,and lower parts of the YRB were 0.51,0.57,and 0.58,respectively,and the time lags were 8 months,6 months,and 6 months,respectively.Further analysis at sub-basin scale and 1°×1° grid scale shown that ENSO's impact on TWSA in the YRB is from east to west,and the intensity gradually decreases from east to west.Meanwhile,the significant correlation between MEI and TWSA in the Yangtze River basin was verified in the frequency domain using fast Fourier transformation(FFT).The accuracy of ENSO-TWSA time lag calculated by cross-correlation analysis was comfirmed through the hydrological data such as rainfall,evaporation,and runoff.Finally,the the significant correlation between ENSO and four extreme floods and droughts occurring in the YRB was revealed.4.The effects of IOD and AO/NAO on the Yangtze River Basin were analyzed through the method of cross-correlation analysis.The results of IOD-TWSA analysis show that the impact of IOD on the YRB is concentrated in the upper YRB.The main manifestations are that positive IOD events will lead to the decline of TWSA in the upper YRB,while negative IOD events will lead to an increase in TWSA in this region.The analysis of water system scale shown that although some upstream water systems were less affected by ENSO,they were significantly affected by IOD.AO-TWSA analysis results shown that AO/NAO would have a significant impact on the YRB.Specifically,positive AO/NAO events would lead to rising TWSA in the YRB,while negative events would lead to a decline.In addition,this effect had a long time lag which reached 16 months.Analysis of the water system scale shown that the influence of AO/NAO in the eastern and southern parts of the YRB was more obvious,while the impact in the west and north was weaker.5.The relationship between different extreme climate events and the TWSA in major river basins in China was analyzed.The impact of ENSO on the mainland of China was discussed on the grid scale of 1°×1°.The results shown that there was a significant correlation between ENSO and most of the basins in China,which was mainly positive except in the Tarim River Basin.The impact was greater on the North China,Central China and East China,while was smaller on the Northeast and South China.The impact of the IOD on China's different basins was more complex.The overall AO/NAO shown a trend from north to south,and it is mainly negatively correlated with TWSA in the northern region,but positively with the southern region.