Abstract
Monitoring the groundwater storage (GWS) changes is crucial to the rational utilization of groundwater and to ecological restoration in the Loess Plateau of China, which is one of the regions with the most extreme ecological environmental damage in the world. In this region, the mass loss caused by coal mining can reach the level of billions of tons per year. For this reason, in this work, in addition to Gravity Recovery and Climate Experiment (GRACE) satellite gravity data and hydrological models, coal mining data were also used to monitor GWS variation in the Loess Plateau during the period of 2005–2014. The GWS changes results from different GRACE solutions, that is, the spherical harmonics (SH) solutions, mascon solutions, and Slepian solutions (which are the Slepian localization of SH solutions), were compared with in situ GWS changes, obtained from 136 groundwater observation wells, and the aim was to acquire the most robust GWS changes. The results showed that the GWS changes from mascon solutions (mascon-GWS) match best with in situ GWS changes, showing the highest correlation coefficient, lowest root mean square error (RMSE) values and nearest annual trend. Therefore, the Mascon-GWS changes are used for the spatial-temporal analysis of GWS changes. Based on which, the groundwater depletion rate of the Loess Plateau was −0.65 ± 0.07 cm/year from 2005–2014, with a more severe consumption rate occurring in its eastern region, reaching about −1.5 cm/year, which is several times greater than those of the other regions. Furthermore, the precipitation and coal mining data were used for analyzing the causes of the groundwater depletion: the results showed that seasonal changes in groundwater storage are closely related to rainfall, but the groundwater consumption is mainly due to human activities; coal mining in particular plays a major role in the serious groundwater consumption in eastern region of the study area. Our results will help in groundwater resource management, ecological restoration, and policy planning for coal mining and economic development.
Highlights
As one of the most fragile ecosystems in the world, the Loess Plateau is characterized by an arid climate, poor vegetation and an annual evaporation much greater than its annual rainfall
Hydrological models have been used to calculate the scale factors for the signal recovery of spherical harmonics (SH) solutions or mascon solutions; these calculations are based on the surface water changes of the Hydrological models which have high correlations with the terrestrial water storage (TWS) changes of the Gravity Recovery and Climate Experiment (GRACE) solutions
By comparing the groundwater storage (GWS) changes results from different GRACE solutions with the in situ GWS changes calculated from 136 groundwater observation wells, we find that the GWS changes from mascon solutions match best with in situ GWS changes, because it shows the highest correlation coefficient, lowest root mean square error (RMSE) values and nearest annual trend, with in situ GWS changes
Summary
As one of the most fragile ecosystems in the world, the Loess Plateau is characterized by an arid climate, poor vegetation and an annual evaporation much greater than its annual rainfall. Groundwater plays a central role in the fresh water supply used for agriculture, industry, and public drinking in the region [1]. This plateau is an important energy base of China and provides large quantities of coal each year. Monitoring the changes of the groundwater reserves in the Loess Plateau over time and space is of great significance. The information concerning groundwater changes is obtained via well observations. This method is time-consuming and labor-intensive but is spatially discontinuous [2]
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