| Since 2002,the launch of the Gravity Recovery and Climate Experiment(GRACE)and its successor satellite GRACE-FO have provided important observation methods for the study of global medium and long-scale changes in surface quality.The accumulated global time-varying gravity field and static gravity field data products in the past 20 years have been widely used in mass migration activities such as earthquakes,changes in land water reserves,glacier movements,surface load deformations,and sea level changes.In the earth's surface water cycle,the global mass redistribution caused by the movement of water bodies has an important impact on the global climate and human production and life.Understanding and studying the mechanisms and changing laws of water quality migration is of great significance to ecological environment protection and human production and life.The GRACE time-varying gravity field model is more sensitive to the medium and long-scale water quality migration,and can be used to monitor changes in regional water reserves.This dissertation mainly analyzes and studies the changes in regional groundwater reserves through the GRACE time-varying gravity field model,surface hydrological model,and GNSS surface elevation changes.First,it summarizes the research progress of time-varying gravity field for groundwater reserve change monitoring and GNSS elevation change inversion of groundwater reserve changes at home and abroad,and then introduces the theoretical methods of time-varying gravity field data processing and GNSS elevation time series analysis.Based on the above theory,the groundwater reserve changes in the North China Plain and California area of the United States were studied and analyzed.The experimental analysis of the thesis mainly includes the following two aspects:(1)Monitoring of changes in underground water reserves of time-varying gravity sites in the North China PlainUsing the time-varying gravity field and surface hydrological model,the scale factor method was used to analyze the temporal and spatial changes of groundwater reserves in the North China Plain since 2002,and the long-term trends of regional groundwater changes were quantitatively calculated.From April 2002 to May 2020,the groundwater was in a state of continuous loss,and the groundwater loss rate was-22.9±1.04mm/yr.The change of groundwater reserves from 2002 to 2014 was-21.0±2.1mm/yr,and the rate of groundwater loss from January 2015 to May 2020 was-12.8±5.39mm/yr;(2)Monitoring of changes in underground water reserves in time-varying gravity sites in California,USAAiming at the characteristics of multi-source and easy-to-obtain data in California,this paper analyzes and studies the temporal and spatial changes of groundwater reserves in California by combining time-varying gravity field,surface hydrological model,precipitation,water wells,GNSS stations and other data,and calculates the long-term change trend of groundwater.From April 2002 to August 2016,groundwater continued to decline.The largest loss area was mainly located in central California.The groundwater loss rate was-9.4±2.1mm/yr,and the precipitation change rate during the same period was-1.0mm/yr.During 2006-2010,the United States experienced a severe drought.The annual average change of groundwater reserves was-39.4±10mm/yr,and the rate of precipitation change during the same period was-5.88mm/yr.During the second drought from 2012 to 2015,the loss rate of groundwater reserves was-44.8.±7.4mm/yr,and the precipitation change rate during the same period is-1.26mm/yr.According to the calculation and analysis of the GNSS station,the P566 station with the most abnormal subsidence in central California reached-52.3mm during 2014-2017,with an annual average of-13.1mm/yr.The water level of the nearby well 362985N1192201W001 dropped in four years.It is about-76.5cm,and the correlation coefficient between-25.65cm/yr is 0.96.The GRACE inversion results are more consistent with the seasonal periodic changes of the GNSS vertical time series. |
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