Regional Climate Change Analysis In China Using GRACE Data And Drought Index

Water is not only an indispensable resource for human existence and major component for living organisms,but also a key factor which affect economic and social development.Accurately acquiring the changes of terrestrial water reserves has important scientific significance and socioeconomic benefits for analyzing the spatial and temporal distribution of regional water reserves changes,understanding largescale hydrological processes,studying regional water resources changes and managing effectively,and forecasting floods and droughts.The GRACE(Gravity Recovery and Climate Experiment)satellite launched in 2002 has made it possible to obtain global and long space scale time-varying gravity field information which is all-weather,high-precision,and high-efficiency.This provides a new method for monitoring changes in the mass of the Earth.This paper will take the Earth's gravity satellite as the starting point,obtained the mean value of the gravity potential by recovering the Earth's gravitational field,and then get the change of the gravitational potential.The change in the gravitational level will be transformed into the change of the terrestrial water resource,then analyse the condition of terrestrial water by using the previous result.The specific work and conclusions of the paper are as follows:(1)Describe the development of satellite gravity detection techniques in space geodetic surveys and three kinds of gravity satellites,then summarize the domestic and foreign research status of using gravity satellite data to detect mass change of the Earth.The GRACE satellite data product was introduced and the principles and methods of recovering global mass changes by GRACE satellite gravity field data were described.Then analyze and compare the Gaussian filtering,destriping filtering,and combination filtering with emphasis by using GRACE time-varying gravity field post-processing methods,and text the effect of extracting regional mass change by using diffirent filtering intensity.(2)Calculated and analyzed the spatial-temporal water storages variations in China,and found that the spatial distribution of terrestrial water storage rate from 2002 to 2015 presented a different trend: In the aspect of land total water storage,the obviously ascending regions are concentrated in Heilongjiang,northeastern regions of Inner Mongolia,central and western regions of China,and the northern Tibetan plateau region,while the significant declines area are concentrated in North China,Xinjiang,and southern Tibet.The North China region as a whole shows a downward trend,and almost all region of Xinjiang also shows a decreasing trend,especially in the northwestern area.The most obvious downward trend was in southern Tibet.The change average rate was about-1.5 cm/yr,and the maximum change rate was up to-1.9 cm/yr.The variation of groundwater reserves calculated by the water balance equation and the measured data of underground stations have very high consistency on both monthly and seasonal scales,which demonstrate the accuracy of recovering groundwater by GRACE data.From the perspective of the distribution of groundwater storage in China,the concentration of groundwater storage has decreased in North China,Xinjiang,and Tibet,and the groundwater content in East China,Southwest China,Qinghai,and Tibet has increased,which means these areas have good situation of groundwater resources.(3)Based on analyze other academician monitor drought by using GRACE data,and improve the previous calculation method,this paper calculate the time series of GRACE-based dimensionless global drought index TDSI(Total Storage Deficit Index)from April 2002 to December 2015 through the improved method,and the new method makes the result have spatially comparable characteristic.Then three kinds of traditional drought indices were calculated in the typical climate regions as Sichuan Province and Xinjiang Province,and compare with TSDI.The results showed that the four drought indices can monitor drought events,but the drought disasters caused by different conditions have their own advantages and disadvantages.The TSDI index calculated by GRACE data provides new ideas and research methods for the monitoring and prevention of drought.