Groundwater storage changes using GRACE observations.

Groundwater is vital for the global water cycle, but it is being depleted at an alarming rate, especially in arid regions. Researchers are looking into new techniques for monitoring changes in groundwater levels in order to evaluate groundwater storage. Different approaches take into account temporal differences in total water storage (TWS). The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) are two satellite missions that are able to monitor water mass changes in a basin and calculate changes in water levels by measuring water variations. The GRACE satellite system has allowed for significant advances in monitoring changes in groundwater levels over large regions. This paper reviews recent studies that used the GRACE mission to show how improved analysis techniques provide greater accuracy in the estimation of mass changes. Moreover, several studies compared the findings of the different GRACE estimates. The findings of these studies are summarized in this paper in order to validate the results of GRACE estimates. The main findings of the literature review showed that aquifer depletion is widespread in areas such as the Middle East, India, China, the United States, and Australia to estimate the change in groundwater level storage in these areas. The California Central Valley and west Africa regions show the most significant groundwater depletion over the past decade, with rates of 24.42± 9.3 km3/year and 14 km3/year respectively, for the period 2003–2015. The middle east experienced a groundwater depletion of around 13±1.5 km3/year from 2002 to 2014. Further investigation will be carried out to understand and evaluate the changes in groundwater levels over large regions. [ABSTRACT FROM AUTHOR]