At least 2 billion people rely on groundwater as the world’s largest and most dependable source of freshwater, with the majority of them living in arid and dry zones (Taylor et al., 2013; Jasechko et al., 2017; Sun et al., 2022). Globally, groundwater is the source of one-third of all freshwater exploitation, supplying an estimated 36%, 42%, and 27% of the water used for domestic, agricultural, and industrial purposes, respectively (Döll et al., 2012). In recent decades, the increased use of groundwater for human consumption and agriculture has led to a decline in groundwater levels in many regions of the globe (Castellazzi et al., 2016; Narany et al., 2017; Cui et al., 2020). As a result, aquifers have been depleting, which has caused a number of environmental and geological problems, including land subsidence and the destruction of wetlands (Dalin et al., 2017). Improving groundwater management is necessary to ensure its sustainable usage and reasonable expansion. Saudi Arabia is regarded as one of the driest countries in the world, despite the fact that 99.84% of the country’s population have access to drinkable water (General Authority of Statistics, 2019). Saudi Arabia only has 89 m³/cap./year of absolute water scarcity, compared to 500 m³/cap./year worldwide. (Water Challenges in KSA, 2021).

In arid and semiarid regions, it is crucial to evaluate groundwater resources, hydrogeologic settings of aquifers, and recharge and/or discharge (natural or anthropogenic) of these systems in order to establish effective management scenarios for these resources and the economic development of such locations (Simmers, 1997). Much of the groundwater in dry regions is used for irrigation, which accounts for roughly 70% of the world’s water withdrawal and 90% of its consumption (Siebert et al., 2010; Gerten et al., 2020).

Groundwater, surface water (dams, reservoirs, rivers, and lakes), snow, soil moisture, plant canopy water, and glaciers all contribute to the total amount of water stored on and below the land’s surface, which is referred to as “terrestrial water storage” (TWS) (Zhu et al., 2021). Changes in the TWS can efficiently indicate the equilibrium or imbalance of water fluxes that are substantially impacted by regional climate conditions (Zhu et al., 2021). Recent global warming has increased TWS variability in many dry and semi arid settings (Wang et al., 2018; Chang et al., 2020; Shugar et al., 2021; Yang, et al., 2022). As a result, correct TWS calculation is critical for understanding regional hydrological processes, which allow effective basin-scale water resource allocation and management.

The goal of groundwater management (Ahamed, et al., 2021) is to develop methods for accurately estimating and monitoring changes in GWS across temporal and spatial scales. Several huge aquifers have been significantly depleted in several regions throughout the world as a result of human activity; these regions include North Africa, South and Central Asia, the Middle East, North China, Australia, and North America (Rodell, et al., 2009; Sun et al., 2022). Historically, scientists have attempted to predict GWS changes using in situ observation (such as monitoring changes in groundwater level), the water balance approach, and hydrological modeling techniques (Ahamed et al., 2021; Sun et al., 2022). Although these techniques have been employed in a number of earlier research, they are constrained by real-world constraints including the dispersed nature of observation wells. Therefore, it remains a significant problem on a global scale to manage refined groundwater resources in a reliable and timely manner, as required.

Several strategies, including physical and chemical methods, in situ measuring, satellite remote sensing, and modeling techniques, have been used to estimate the TWS and assess the recharge, discharge, and depletion rates of aquifer systems, as well as to investigate the connectivity of their subbasins (Cox and Chao, 2002; de Vries and Simmers, 2002; Cazenave and Nerem, 2002; Scanlon et al., 2016; Ramillien et al., 2005; Rodell et al., 2009). These methods are difficult to use on a regional scale, and their results are sometimes suspicious due to the scarcity of datasets required for implementation, as well as the substantial efforts and resources required to obtain them. Satellite remote sensing only captures information on surface water bodies, and the precision of model parameters influences numerical modeling. Fortunately, the implementation of the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) can address these shortcomings and limitations by providing a new remote sensing technique for monitoring monthly TWS (Chen et al., 2016).

As a twin satellite-to-satellite monitoring mission, the GRACE mission started in March 2002 enables us to compute the average and time-varying components of the Earth’s gravitational field (Tapley et al., 2004). Hydrological signals dominate the gravitational field’s change, hence GRACE data can be used to correctly quantify TWS fluctuations (Ahmed, et al., 2014; Tapley et al., 2019). GRACE can detect water storage changes to within 1–1.5 cm worldwide (Wahr et al., 2004), despite having a poorer spatial resolution (300 km). The GRACE mission terminated in October of 2017, however the mission that replaced it, which began operations in May 2018, is still delivering consistent data for hydrological uses (Landerer et al., 2020).

Because GRACE can be utilized to fill in the gaps in hydrological monitoring data, some studies have combined GRACE with other data to estimate depletion and/or recharge rates caused by climate and/or human activities in Saudi Arabia and other regions (e.g., Fallatah et al., 2017; 2019; Mohamed, 2019; Mohamed, 2020a; Mohamed, 2020b; Mohamed, 2020c; Mohamed et al., 2021; Mohamed and Gonçalvès, 2021; Taha et al., 2021; Mohamed, 2022a; Mohamed, 2022b; Mohamed, 2022c; Mohamed, 2023a; Mohamed, 2023b; Othman et al., 2022; Alshehri and Mohamed, 2023). Other satellite and aerial geophysical field datasets have been utilized to explore continental crustal properties (Mohamed and Al Deep. 2021), Curie point depth and magma chamber geometry (Mohamed et al., 2022d), and subsurface structures controlling the mineralization zones (Mohamed et al., 2022e; Mohamed et al., 2023).

More accurate estimate of the depletion rate of the Wadi Ar-Ramah basin was obtained in this work by combining GRACE data with results from land surface models (LSMs) for the time period of 04/2002 to 12/2021. The objectives of this study are to: 1) use improved state-of-the-art solutions, the global mass concentration solutions (mascons) covering the time of April 2002 to December 2021; 2) using outputs from three versions of the Global Land Data Assimilation System (GLDAS) to estimate the groundwater storage (ΔGWS) from the GARCE-derived ΔTWS, and define its controlling factors; and 3) assess if the basin is in steady-state conditions or is being exhausted, and, if the latter, whether this depletion is due to natural and/or anthropogenic factors.

With a length of about 600 km, Wadi Ar-Ramah is a long river valley on the Arabian Peninsula (370 mi; Figure 1). The wadi begins near Medina in Jibl al Abyad (the White Mountain), where it is mostly dry and partially dammed by expanding sand dunes. A number of smaller wadis, including Murghala Wadi, Mohalla Wadi, Jarir Wadi, and Jifn Wadi, are connected to it as it flows towards the north-east. In Al-Qassim Province close to Buraidah, it comes to an end in the Thuayrat Dunes of the ad-Dahna Desert. After there, the wadi disappears beneath the sand dunes, where it is known as Mistewy Wadi. It appears as Wadi al-Batin on the other side of the sand dunes, which runs about 425 km north to define Kuwait’s western boundary. It finally drains into the Arabiani Gulf (Edwards, et al., 1970; Helen Chapin Metz, 1992; Wadi al-Ramah, 2011).

The valley is wide because it was previously a prominent river valley. It was originally a 1,200-km-long river that flowed from Medina to the Arabian Gulf roughly 10,000 years ago (according to Dr. Abdullah Al-Musnad). Drought conditions and sand migration at Althwairat and Dahna caused the valley’s route to be divided into three sections: Wadi al-Ramah, the longest at 600 km, Wadi Aloddi, at 45 km, and Wadi al-Batin, at 450 km. According to geological studies, the Wadi Ar-Ramah flows fully three times per hundred years. Recently, it flowed in the years of (1945, 1982, 1987, 2004, 2008, and 2018). The river valley flooded for afew days in 1818, 1838, 1987, and 2008. The wadi overflowed in 1838, generating a lake with an area of 520 km² that continued 2 years and attracted rare water birds to the region (alriyadh.com; Wadi al-Ramah, 2011).

The research region contains two surface rock units representing different geologic time periods, namely, the Cambro-Ordovician and Quaternary. Except for the eastern and northeastern parts of the study area, which are covered by sand dunes, the Saq Sandstone aquifer outcrops on both sides of the wadi. This Cambrian-Ordovician sandstone has several colors and is interbedded with jointed quartz (Bramkamp et al., 1963; Sowayan and Allayla, 1989). This Sandstone outcrop stretches 170 kilometers south of the wadi and north across the Syrina border. It has a surface area of around 65,000 km². The Saq Sandstone is the country’s oldest sedimantary unit, and it unconfromably overlies the underlying crystalline rocks. The Tabuk Formation, which is represented by alternating sandstone and shale elements, is likewise an important water-bearing reservoir. Eolian and fluvial deposits make up the more recent Quaternary sediments. Eolian sediments are made up of many forms of undulating sand sheets. These sands impact the width of the wadi, which is around 1 km in the eastern part near the downstrem compared to nearly 14 km in the western poerion of the study area (Sowayan and Allayla, 1989). The wadi channed and its floodplain are occupied by fluvial deposits. The Saq Sandstone is the main imprtnat aquifer in the research area, spreading for long distances north and south. This aquifer becomes cofined to the east with good water quality, however higher salinity values occur locally in the study region (Sowayan and Allayla, 1989).

In this study, we integrate GRACE and GLDAS data to get a comprehensive understanding of the groundwater potentialities of Wadi Ar-Ramah in Saudi Arabia’s eastern region.

Based on an analysis of rainfall data for the Wadi Ar-Ramah between April 2002 and December 2021, the annual precipitation rate is 87.7 mm. Wadi Ar-Ramah Basin has been subjected to extensive groundwater extraction since 1990. The integrated results from GRACE and GLDAS indicate that the groundwater resource is declining at a rate of −1.212 ± 0.012 cm/year. The identification of change from Landsat images has revealed significant land use/land cover changes since 1985. The substantial rate of groundwater extraction is not mitigated by the small amount of surface water derived from precipitation. In the aquifer’s downstream section, the higher sediment succession of 4,000–6,000 m is preserving vast quantities of groundwater. Using the Wadi Ar-Ramah Basin, we demonstrated that GRACE data can be used to estimate mass variations across enormous hydrologic basins, a normally challenging endeavor. Despite the unavoidable challenges, the current research advances our knowledge of the groundwater variability from both a present and a future perspective. Policymakers may use this information to increase groundwater-dependent agriculture and community development. A continuous monitoring program using the most recent GARCE data, meteorological models, and ground-based data should be carried out to evaluate the water storage dynamics in the future.