The Research On Spatiotemporal Characteristics Of Groundwater Storage Change In Beijing-Tianjin-Hebei Region

The rapidly decrease of groundwater resources under the effects of natural and anthropogenic factors,especially in the urban agglomeration where the cities gather and grow.It has caused a series of ecological and environmental problems such as surface subsidence,which seriously threaten the regional ecological security and sustainable development.The GRACE satellite can accurately quantify groundwater reserve through gravity measurements.It overcomes the problems of traditional groundwater monitoring methods that are difficult to get groundwater dynamics at a regional scale due to the limited number and uneven distribution of observations.However,the current studies based on GRACE mainly focus on large-and medium-sized natural watersheds(or regions),but less attention has been paid to urban areas.Moreover,the exploration of driving factors of groundwater change in large urban agglomerations region has not enough.For better promoting the management and protection of groundwater resources in Beijing-TianjinHebei region(BTH),it is very important to analyze the variation characteristics and driving factors of groundwater storage change.Based on GRACE and GLDAS data in the BTH,this paper assessed the spatial and temporal characteristics of dynamic groundwater storage changes during 2002 to 2017 from two perspectives including natural watershed and urban agglomeration.In each perspective,the groundwater storage changes were investigated from different scales of the whole and the part.And then,the driving factors for groundwater storage change in urban agglomeration were emphatically analyzed.The main results were as follows:The groundwater change of Haihe River Basin was studied from two scale of the whole basin and four sub-basins.It was found that the groundwater storage of the whole basin continued to decline,and the rate of decline of each sub-basin was different.The correlation coefficient verified by 90 in-situ observations was 0.95,which proved that the inversion results were effective.The average groundwater change in Haihe River Basin from 2002 to 2017 was-1.22CM/ year,and the annual fluctuation was basically consistent with the rainy season.Among the four sub-basins,the groundwater storage in the sub-basin of the southern Haihe basin was decreasing at a rate of1.54 CM per year,which is nearly twice as fast as that in the Luanhe River basin and the coastal river basin in eastern Hebei Province.The spatial variation of groundwater storage in the haihe River Basin can be divided into three main modes,and the interpretation rate of the first mode was95.31%,which reflected that the groundwater storage change in Haihe River Basin behaved consistently descending with the spatial pattern in southwest-northeast direction.The groundwater change of Beijing-Tianjin-Hebei urban agglomeration was studied across regional-and city-scale.It was found that the decline of groundwater in the southern cities is more serious than that in the northern cities.The integration policy and the South-to-North Water Transfer will affect the distribution pattern of the groundwater storage change.There was a decreasing trend from 2002 to 2017,with an average change of-1.20CM/ year,and the decreasing rate slowed down after 2010.The decline rate of Handan was 1.93CM/ year,which was 3.5 times that of Tangshan in the north.There was a significant positive spatial correlation between the groundwater storage changes among cities,and the utilization of water resources will affect the distribution of the groundwater storage change.The spatial inverting of cold and hot spots during the period showed that the cities with fast groundwater decline shifted from north to south.In the BTH,the impact of human activities on groundwater change was greater than that of natural factors.The agricultural water consumption was the primary factor for the decline of groundwater storage in Beijing-Tianjin-Hebei.Reducing agricultural water consumption is an important way to protect groundwater resources in the BTH.Based on different spatial scales,this study quantitatively evaluated the spatial-temporal variation characteristics of groundwater storage in urban agglomerations in China.By analyzing the driving mechanism of groundwater storage change,the paper revealed the importance of balancing urban development and agricultural water demand,as well as the allocation of water diversion for groundwater protection.The results extends previous studies on urban groundwater dynamics change,and also may contribute to promoting the synergic plan and management of water resource allocation for groundwater protection.