Using GRACE Data To Study Regional Drought And Groundwater Changes In China

China has a vast territory,in some areas geographical location is complex,climate is changing and drought is frequent.At the same time,in some areas agricultural water use efficiency is low,groundwater exploitation is serious and environmental problems caused by over-exploitation of groundwater are increasingly prominent.In this paper,the GRACE(Gravity Recovery and Climate Experiment)time-varying gravity field model and other data are used to study the drought and groundwater changes in the plains of the middle and lower reaches of the Yangtze River,the southwestern region,and the North China Plain.It has a positive effect on guiding China's drought relief work,rational using groundwater resources,ensuring the sustainable development of groundwater resources.The time-varying gravity model data of 2003.1~2012.12 issued by CSR(Center for Space Research)is used to invert the monthly average of the three-regional terrestrial water reserves.The filtering method is Gaussian filtering with a radius of 400 km and improved decorrelation filtering.Combined with precipitation data analysis,it can be seen that the precipitation and terrestrial water reserves in the plains of the middle and lower reaches of the Yangtze River are correspondingly better.The terrestrial water reserves in the North China Plain may have a lag period relative to the precipitation.The time series of land water reserves in the three regions was obtained by a single scale factor recovery method.The lowest value of land water reserves of the middle and lower reaches in the Yangtze River and the North China Plain was in May 2011,the lowest value of the southwest region was in March 2010.It can be preliminarily determined that drought occurs in the three regions during the corresponding time period.Combined with the drought index data released by the European Drought Research Center,the drought detection results of the GRACE time-varying gravity field model data were verified to be accurate.It can be known that the main reason for the drought in the middle and lower reaches of the Yangtze River and the North China Plain was the low precipitation in May 2011.In March 2010,the temperature in the southwest region was higher and the evaporation was larger to cause drought.The groundwater reserves in the middle and lower reaches of the Yangtze River and the southwestern region showed an upward trend with a rate of 5.2 ? 0.85 mm/year and 3.6 ?0.66mm/year.The North China Plain showed a trend of decreasing groundwater reserves at a rate of-5.5 ? 0.96 mm/year.The groundwater in the middle and lower reaches of the Yangtze River and the southwestern region are high in summer and low in winter,which is consistent with the agricultural farming patterns of the two places.In summer,the increase of groundwater is supplemented.In winter,the crops are irrigated by groundwater.There are obvious north-south differences in the variation of groundwater reserves in the middle and lower reaches of the Yangtze River.The main reason may be that the winter wheat in the north of the Yangtze River has obvious wintering period.The winter wheat in the south of the Yangtze River has no wintering period.The summer main crop in the south of the Yangtze River is double-season rice and the main summer crop in the north of the Yangtze River is single-season rice.The water demand of the two rice types is different in the growth cycle.The groundwater in the North China Plain is high in winter and low in late spring and early summer,which is related to the water use of crops in the North China Plain.Winter wheat has less irrigation water for the wintering period.In the late spring and early summer,it is in the rotation period of winter wheat and summer corn.The precipitation can't meet the agricultural water,which leads to the increase of groundwater exploitation.The main influencing factors of groundwater changes in the three regions in summer are precipitation,the winter is mainly human factors namely agricultural irrigation.The groundwater reserve during the dry period is significantly lower than the historical value of the adjacent years,which may be related to the increase of the amount of groundwater dependence in the dry period.