Reconstruction Of Water Storage Change And Drought Monitoring In The Yangtze River Basin Combining Satellite Gravity And Hydrological Data

Terrestrial Water Storage Change is not only one of the most important part of global water cycle,but also one of crucial index to explore the new pattern of water exchange between atmosphere,land and sea,to monitor water migration and balance state,to prevent extreme hydrometeorological disasters.Compared with traditional approach,the method based on GRACE and GRACE-FO satellites provides a new idea for obtaining large-scale,high-precision,long-term and high-stability water storage change series,evaluating regional water balance state and long-term trend,capturing and predicting extreme hydrological meteorological disasters.However,there is an 11-months interval between GRACE and GRACE-FO missions,which affects the continuity analysis of water storage changes.The Yangtze River basin is the largest basin of China.Due to the impact of climate change,drought events have occurred frequently during the past half century,posing a great threat to social and economic development and the safety of people's lives and property.As a result,monitoring intensity and frequency of drought events in Yangtze river basin,evaluating drought influence and impact range comprehensively,forecasting regional drought risk in the future,are important to ensure food and water security,maintain the ecological environment sustainable development,and guide the construction of national security strategy formulation.In this article,based on GRACE,GRACE-FO satellite gravity data and multi-source hydrometeorological materials from 2002 to 2020,we analysis the spatio-temporal distribution law rules of water storage change of the Yangtze river basin.Further,multi-scale monitoring of drought events is carried out to provide theoretical and data support for the prevention and control of drought in the future.The main research contents and results of this article are as following:(1)Introduced the data processing method of GRACE time-varying gravity field.The spherical harmonic coefficient and Mascon products released by GRACE were compared and analyzed under different processing methods.Among them,spherical harmonic coefficient products are released in the form of dimensionless stokes coefficient,which requires corresponding processing work such as background field deduction,low-order term replacement,spatial filtering,etc.Its advantages include various processing methods,strong adaptability,wide application range,high inversion accuracy,and so on.Mascon products are released in the form of equivalent water height,which can be directly used,but faced with problems such as low spatial resolution and poor fitting effect in some regions.(2)A simple algorithm is proposed to complete the gap period between GRACE and GRACE-FO missions.Based on the characteristics of water balance in the basin,GRACE,GRACE-FO and multi-source hydrometeorological data were used to reconstruct the 11-months interval using the least square fitting method.Validation results show that the reconstruction method has high stability and accuracy,and its performance is excellent under different input conditions and spatial scales.The reconstructed time series not only accurately reflected the long-term water storage change and distribution characteristics of the Yangtze River basin,but also monitored the drought event in the southern part of the Jinshajiang River basin in the spring of2018.Then,we promote the reconstruction method to the whole China.Based on the reconstructed water storage change series,four abnormal regions were detected in the central and southern Xinjiang,the boundary area of Xinjiang,Tibetan and Qinghai provinces,the eastern Tibet,and the North China Plain.It is speculated that these abnormal phenomena are the result of the combined actions of natural factors and human activities.(3)The drought event monitoring method based on GRACE TWSC data was explored.Based on GRACE and GRACE-FO data,the GRACE drought index(GRACE-DSI)was obtained,and used to identified the drought events in the Yangtze River basin using the run theory effectively.Results show that GRACE-DSI has a strong sensitivity to the drought in Chongqing in 2006,which is consistent with results from SPI and SPEI and significantly better than that from PDSI.(4)Combined with GRACE-DSI and SPI,drought events in the Yangtze River Basin in recent 20 years were analyzed.Use GRACE-DSI statistics and analysed the drought in the Yangtze River basin in 2002-2020,and compared with SPI.The results show that there were 18 severe drought events in the Yangtze River basin from 2002 to2020,among which the most severe drought occurred in the middle-lower Yangtze River basin and part of the upper reaches during the winter of 2010 to the winter of2011.This drought lasted 13 months,and the intensities of GRACE-DSI and SPI reached 18.23 and 6.63,respectively.The drought reached the vertices in April and May 2011,that 56.25% and 58.23% regions of the Yangtze River basin reached the standard of extreme drought,respectively,and the proportions were reached to 96.31%and 94.64% in the middle-low Yangtze River basin.The correlation between GRACEDSI and SPI is relatively high,and the correlation coefficient is weak in the east and strong in the west,weak in the north and strong in the south,which may be related to the climatic conditions in different regions of the Yangtze River basin.