Detecting Regional Terrestrial Water Storage Changes And Ice-Sheets Mass Loss Under The Extreme Climatic Events By GRACE And GRACE-FO

With global warming,the terrestrial water storage changes in typical regions affected by climate factors will cause the droughts or floods,the glaciers in Antarctica and Greenland will melt more rapidly,and global mean sea levels will rise and fall sharply.The quantitation of interannual variations of terrestrial water in typical regions,melting of glaciers in Antarctica and Greenland,and global sea level fluctuations is significant to understand the changes of global climate.GRACE(Gravity Recovery and Climate Experiment)and GRACE-FO(Gravity Recovery and Climate Experiment Follow-on)satellites,as the original geodetic observation technology,are providing new insights into the hydrosphere in the Earth system including terrestrial water storage changes in typical regions,melting of glaciers in Antarctica and Greenland,and global mean sea level changes.In this dissertation,we first describe the backgrounds and motivations about why to study the regional TWS and GMSL.Then,we introduce the theory of time-variable gravity field and procedures of post-processing.Finally,we present the results of regional TWS and GMSL as follows:1.We used the multi-source remote-sensing satellites(GRACE,GRACE-FO,and MODIS)products,hydrological models,and in-situ data to:(1)present water losses(including TWS,Mean SWS,and GWS)and vegetation degradations in southeastern Australia during two bushfire seasons;(2)discuss the difference between precipitation-driven derived TWS and GRACE/GRACE-FO TWS which may denote the fire-induced water loss;(3)investigate the potential connections among climate indices(including El Nino event and a positive phase of IOD),water cycle,and bushfires.2.The interannual variations of GRACE TWS(Terrestrial Water Storage),SMS(Soil Moisture Storage),Precipitation(P)and their correlations to ENSO are shown in the ten basins of China.The typical ENSO-related regions were in the middle and lower reaches of Yangtze River Basin(YRB)and the Southeastern River Basin(SRB),with the maximum correlation coefficients of 0.55,0.78 and 0.70,respectively.The anomalies of TWS in these typical ENSO-related regions lagged ENSO by～7 months,～5 months,～5 months,respectively.During the period of 2010/2011 La Nina,the water scarcity of the lower reach of YRB and the SRB occurred from April to May in 2016,and the water loss in middle reach of YRB occurred after 1-2 months.During the period of 2015/2016 El Nino,TWS increased continuously in the middle and lower reaches of YRB,and the SRB while the ENSO index showed significant positive value from autumn-winter of 2015 to early 2016.Besides,the TWS anomalies in July 2016 was caused by the lagged effect of the persistent abnormal anticyclonic circulation in the western North Pacific.3.The rates of ice mass loss are 119±23 Gton·yr-1、259±20 Gton·yr-1 from April 2002 to March 2020,which are equivalent to the rise of global sea level with～0.33 mm·yr-1 and 0.74 mm·yr-1,respectively.We also find that:1)the rate of ice mass loss over 2009-2019 was ten times than that from 2002-2009 in Antarctic Wilks Land;2)Greenland’s abrupt ablation happened in the summer and autumn of 2019 was similar with that in the summer and autumn of 2016,which was affected by the summer NAO index;3)replacing C30 or not may make the maximum difference up to 40%in Antarctica but 3%in Greenland.Besides,we also introduced Swarm-derived time-varied gravity and the mathematical method to cover about one-year gap between GRACE and GRACE-FO missions.4.We utilized the Altimetry,GRACE,and Argo data to show the changes of sea level in 2010-2012 La Nina and 2014-2016 El Nino events,respectively.During the period of 2010/2012 La Nina,GMSL decreased 7.6 mm,the contributions from ocean mass was about 5.1mm which was about twice than the steric components.From 2010 to 2013,GMSL decreased 19.2 mm,ocean mass contributed to 12.3 mm.From 2014 to 2016,GMSL increased 15.1 mm and the ocean component contributed over 90%.Besides,the rise of GMSL in 2014-2016 El Nino may come from the decrease in TWS from four major typical regions named Australia,Southeast Asia,and South America.