Understanding surface-groundwater interactions is essential for sustainable water resource management in arid regions, where water scarcity and water quality degradation pose critical challenges. This study explored the hydrochemical characteristics, dominant controlling processes, and linkages between surface water and groundwater in the arid Middle Egypt basin. Hydrochemical facies and major physicochemical parameters were compared for both water types, supported by multivariate statistics (principal component analysis and PER-MANOVA) and machine-learning approaches (Random Forest and a hybrid K-nearest neighbor model). Results revealed distinct hydrochemical signatures, with surface waters characterized mainly by bicarbonate facies and groundwater exhibiting more mineralized sodium chloride and calcium chloride facies. Hydrochemical patterns suggest that surface water chemistry is influenced by evaporative concentration, whereas groundwater composition reflects mineral dissolution and cation exchange; however, these process interpretations are considered first-order and indicative rather than diagnostic. Random Forest analysis identified total cations, total anions, and electrical conductivity as the most important variables discriminating between surface water and groundwater. The hybrid KNN model indicated that surface water chemistry alone provided the strongest basis for predicting groundwater composition, with relatively high performance for Na, Cl, and Mg (R2 = 0.71-0.84) but weak performance for hardness and sulfate. Chemical similarity showed no systematic distance-decay relationship, and spatial proximity was not a primary control on surface-groundwater chemical relationships. These findings highlight contrasting hydrogeochemical controls on surface water and groundwater in the Nile Valley and demonstrate the value of integrating hydrochemical analysis with machine-learning tools for improving understanding of surface-groundwater interactions in arid environments.

This study aims to assess the vulnerability of groundwater in the Nile Delta to contamination and evaluate its suitability for drinking and irrigation. A total of 28 groundwater wells (ranging from 23 to 120 m in depth) and two Nile surface water samples were analyzed for total dissolved solids (TDS), heavy metals, groundwater quality index (GWQI), and hazard quotient (HQ). The findings reveal that deep groundwater (60–120 m) displays paleo-water characteristics, with low TDS, total hardness, and minimal heavy metal contamination. In contrast, shallow groundwater (<60 m) is categorized into three groups: paleo-water-like, recent Nile water with elevated TDS and heavy metals, and mixed water. Most groundwater samples (64%) are of the Ca-HCO3 type, while 28% are Na-HCO3, and 8% are Na-Cl, the latter associated with sewage infiltration. Most groundwater samples were deemed suitable for irrigation, but drinking water quality varied significantly—4% were classified as “excellent”, 64% as “good”, and 32% as “poor”. HQ analysis identified manganese as a significant health risk, with 56% of shallow groundwater samples exceeding safe levels. These findings highlight the varying groundwater quality in the Nile Delta, emphasizing concerns regarding health risks from heavy metals, particularly manganese, and the need for improved monitoring and management.

Global energy demand has risen sharply, intensifying concerns over greenhouse gas emissions and climate change. Fossil fuel combustion remains the primary driver of increasing carbon dioxide levels. A rapid transition to clean energy sources is therefore imperative. Dark fermentative biohydrogen production (DFHP) has been investigated as a scalable, low-carbon hydrogen (H2) pathway that leverages organic waste and industrial waste heat. The study objectives were to quantify research evolution, assess techno-economic performance, and propose sustainable deployment pathways. Bibliometric analysis was performed on 435 Scopus records, yielding an annual growth rate of 19.6 % and 928 unique keywords. Besides, bibliometric trends were visualised using VOSviewer, Biblioshiny, and Graphica software. For techno-economic evaluation, H2 conversion efficiencies, water requirements, and cost impacts under waste-heat integration were compared against conventional H2 production methods. DFHP was shown to operate in standard fermenters with negligible water demand. Wasteheat integration was demonstrated to eliminate external heating costs and lower levelized H2 costs. Key technical and operational challenges were identified, including feedstock variability, volatile metabolite inhibition, and mass- and heat-transfer limitations at scale. Sustainable pathways were outlined, emphasizing low-energy pretreatment, in situ metabolite removal, advanced reactor geometries, and inclusive capacity-building partnerships co-located with waste-processing facilities. Alignment with sustainable development goals (SDGs) for affordable clean energy, responsible consumption, and climate action was highlighted. A clear roadmap has been provided to advance global decarbonization efforts and to accelerate the deployment of a resilient H2 economy.

Groundwater salinity hotspots in shallow aquifers have been reported across various geographical and climatic settings. These hotspots are commonly linked to anthropogenic influences, particularly irrigation return flow, in arid, unconfined aquifers under intensive irrigation. However, the interplay of geological and hydrochemical processes in shaping salinity variation and hotspots formation remains insufficiently understood. This study integrates hydrochemical, isotopic, multivariate statistical, and geophysical methods to better understand the regional distribution and origin of groundwater hotspots in the newly reclaimed areas of the Eastern Sahara, along the desert fringes of the Nile River. The findings suggest that salinization in the aquifer is influenced by evaporite dissolution, silicate weathering, salts leaching, ion exchange, and groundwater mixing processes, with significant anthropogenic contributions from irrigation return flow and fertilizer application. Notably, we report for the first time that salt-rich marine clay layers, which were left unflushed during the evolution of the Nile River, serve as the primary source of salinity hotspots. These clay layers act as natural barriers, restricting groundwater exchange with the Quaternary Nile aquifer while promoting salinization through saline/formation water upconing due to excessive groundwater pumping. Furthermore, inefficient irrigation practices add more water through irrigation return flow to the sandy alluvium aquifer, which exacerbates the groundwater salinity and ultimately leads to the development of waterlogged areas. These findings highlight the significant impact of river system evolution dynamics on groundwater quality and call for revisiting the current irrigation strategies in the newly reclaimed areas along the Nile River's desert fringes.

The global need for energy has risen sharply recently. A global shift to clean energy is urgently needed to avoid catastrophic climate impacts. Hydrogen (H2) has emerged as a potential alternative energy source with near-net-zero emissions. In the African continent, for sustainable access to clean energy and the transition away from fossil fuels, this paper presents a new approach through which waste energy can produce green hydrogen from biomass. Bio-based hydrogen employing organic waste and biomass is recommended using biological (anaerobic digestion and fermentation) processes for scalable, cheaper, and low-carbon hydrogen. By reviewing all methods for producing green hydrogen, dark fermentation can be applied in developed and developing countries without putting pressure on natural resources such as freshwater and rare metals, the primary feedstocks used in producing green hydrogen by electrolysis. It can be expanded to produce medium- and long-term green hydrogen without relying heavily on energy sources or building expensive infrastructure. Implementing the dark fermentation process can support poor communities in producing green hydrogen as an energy source regardless of political and tribal conflicts, unlike other methods that require political stability. In addition, this approach does not require the approval of new legislation. Such processes can ensure the minimization of waste and greenhouse gases. To achieve cost reduction in hydrogen production by 2030, governments should develop a strategy to expand the use of dark fermentation reactors and utilize hot water from various industrial processes (waste energy recovery from hot wastewater).

Egypt faces a critical challenge of water scarcity driven by rapid population growth, climate change, and geopolitical tensions, particularly concerning the Grand Ethiopian Renaissance Dam. In arid regions such as the Eastern Desert plateau between Minia and Beni Suef, developing robust models for groundwater exploration is vital. This study presents an integrated geo-electrical modeling approach that synthesizes Vertical Electrical Sounding (VES) data, satellite remote sensing, and digital elevation models (DEMs) to delineate and evaluate groundwater-bearing formations. A total of 44 VES points, using the Schlumberger configuration (AB = 3–1000 m), were analyzed and constrained by lithological data from five boreholes. The resulting resistivity model reveals a consistent four-layer electrostratigraphy: a high-resistivity flinty limestone, overlying two marl layers (the lower of which is water-bearing), and underlain by a nummulitic fractured limestone aquifer of the Samalut Formation. The marl aquifer exhibits resistivities of 21.5–38.8 Ω·m at depths of 60–120 m, while the deeper aquifer ranges from 116–223 Ω·m and occurs between 170–300 m. Integration with 2-D resistivity profiles and a 3-D depth model reveals three NW–SE trending step-like normal faults that control aquifer geometry and thickness, with Fault F2 acting as a major boundary influencing facies distribution. This study introduces an original 3D structural-hydrostratigraphic model that integrates geomorphologic, tectonic, and geophysical datasets, offering an effective decision-support tool for sustainable groundwater development. The model framework aligns with contemporary earth system modeling efforts and is scalable for application in other structurally complex arid regions.

Around the world, groundwater supply is critical for vital needs such as drinking and irrigation. This work investigates groundwater in the carbonate aquifer of the Middle Miocene in the east El Minia area, Egypt. In this regard, thirty-two groundwater samples were collected. The water samples were analyzed for Ca2+, Mg2+, Na+, K+, Cl−, SO42−, NO3−, CO2−, HCO3−, Fe, Mn, Cd, As, Cr, Cu, and Pb. Groundwater has been evaluated using two methods, which are water quality index (WQI) and health risk assessment (HRA). The predominant groundwater is soft water, and the samples range in salinity from fresh to slightly salty. The groundwater mostly falls into the alkaline water type. All the groundwater samples under study are deemed low quality for human consumption due to water contamination. Fe, Mn, Cd, Cu, and Pb have high HQnc values, which can result in non-carcinogenic health issues in adults, while Mn, Cu, and Pb can give rise to non-carcinogenic health issues in children.

Using geochemical and pumping test data from 80 groundwater wells, the chemical, hydrologic, and hydraulic properties of the fractured Eocene carbonate aquifer located west of the Al-Minya district, the Western Desert, Egypt, have been characterized and determined to guarantee sustainable management of groundwater resources under large-scale desert reclamation projects. The hydrochemical data show that groundwater from the fractured Eocene carbonate aquifer has a high concentration of Na+ and Cl− and varies in salinity from 2176 to 2912 mg/L (brackish water). Water–rock interaction and ion exchange processes are the most dominant processes controlling groundwater composition. The carbonate aquifer exists under confined to semi-confined conditions, and the depth to groundwater increases eastward. From the potentiometric head data, deep-seated faults are the suggested pathways for gas-rich water ascending from the deep Nubian aquifer system into the overlying shallow carbonate aquifer. This mechanism enhances the dissolution and karstification of carbonate rocks, especially in the vicinity of faulted sites, and is supported by the significant loss of mud circulation during well drilling operations. The average estimated hydraulic parameters, based on the analysis of step-drawdown, long-duration pumping and recovery tests, indicate that the Eocene carbonate aquifer has a wide range of transmissivity (T) that is between 336.39 and 389,309.28 m2/d (average: 18,405.21 m2/d), hydraulic conductivity (K) between 1.31 and 1420.84 m/d (average: 70.29 m/d), and specific capacity (Sc) between 44.4 and 17,376.24 m2/d (average: 45.24 m2/d). On the other hand, the performance characteristics of drilled wells show that well efficiency ranges between 0.47 and 97.08%, and well losses range between 2.92 and 99.53%. In addition to variations in carbonate aquifer thickness and clay/shale content, the existence of strong karstification features, i.e., fissures, fractures or caverns, and solution cavities, in the Eocene carbonate aquifer are responsible for variability in the K and T values. The observed high well losses might be related to turbulent flow within and adjacent to the wells drilled in conductive fracture zones. The current approach can be further used to enhance local aquifer models and improve strategies for identifying the most productive zones in similar aquifer systems.

Among crucial factors that control flooding events are extreme climate, urban growth, and mismanagement. Islands in the Nile River have experienced successive cycles of flooding and drying due to recent rainy years in the Nile Basin countries. This paper focuses on the impact of floods on the amounts of ammonium-N released, total concentrations of heavy metals, enzyme activities, and microbial biomass (C and N) in flood soils of 11 Nile River islands. Field moist soils and their airdried counterparts were collected from the outskirts of the island and incubated for 15 days at 30 °C to be analyzed. Results reflected that the amounts of released NH4-N were higher in airdried than in wet soils. The average hydrolysis rates of the studied six enzyme substrates were correlated significantly with organic C, organic N, microbial bio-mass C and N in the field moist soils. The highest correlation coefficients (r) were with rates of hydrolysis of substrates of asparaginase, amidase, and β-glycosaminidase. A significant intercorrelation between rates of hydrolysis of the six studied enzyme substrates and r values which range from 0.81 to 0.98. At 10 mmol kg−1 soil, Co+2, Cd+2, Pb+2, Cu+2, Cr+3, and Ni+2 inhibited the release of NH4-N. Arginine hydrolysis was inhibited by the six heavy metals at 5 mmol kg−1 soil; the most effective inhibitors were Pb+2, Ni+2, and Cr+3. Due to the complex soil enzymatic and organic nitrogen hydrolase activities that occur during floods, fertile fields on the Nile River islands should not be fertilized before the summer flood seasons, which will prevent contamination of the Nile River water and loss of its island soil fertility.

The Wadi El-Rayan lakes are important aquatic environments located at the border of the great North African Sahara. Quantifying the temporal changes in these lakes due to natural and/or anthropogenic stressors is critical when assessing potential impacts on aquatic ecosystem health and the sustainability of fisheries. To detect the changes in fish communities and their drivers, the landing composition of the Wadi El-Rayan lakes over the past 30 years was quantitatively analyzed. The areas of the lakes dramatically decreased from 110 km2 in 1991 to 73 km2 in 2019. The loss of the lake area was attributed to climate warming, where the evaporation rate exceeded the volume of recharge and the recharge decreased due to an increase in agriculture and aquaculture. The total landing significantly increased in the past three decades due to an increase in the fishing effort (number of licensed boats). Nile tilapia, mullet, and grass carp dominated the landings. The pelagic-to-demersal ratio indicated a shift in the fish community composition towards demersal species. This shift was attributed to an increase in the eutrophication level. The fish communities of the landing data were clustered into four distinct groups. These clusters were significantly differentiated (p < 0.001) in both a PERMANOVA test and a PCA plot. There was a gradual replacement of the dominant species among these clusters. The most recent cluster (2018–2019) was characterized by rare species dominating the community. This shift in species composition suggests that target taxa may have been overexploited. The total landing also decreased, which may have been a result of climate warming. Furthermore, the presence of alien and warm-water species significantly increased. The fish community structure and composition shift could be attributed to anthropogenic (mismanagement) and natural climatic changes (warming).

Water pollution with potentially toxic elements (PTEs) becomes a major threat to the validity of that water for drinking and agriculture and hence human life. The current study aims to evaluate the carbonate aquifer groundwater PTE content, sources, and impact on water quality. To achieve this goal, drilling cutoff of two wells and 30 groundwater samples were collected and chemically analyzed. The groundwater has TDS values ranged from 271.2 to 971.8 mg/l. Freshwater recharge process led to the continuous freshening of the aquifer and enhanced the forward ion exchange reactions. Carbonate and evaporate mineral dissolution/precipitation processes are the main controller of groundwater chemistry. Cd and As represented the most hazardous elements in these rocks followed by Pb. The presence of high concentrations of PTEs (As, Cd, Cr, and Pb) in water-bearing carbonate rocks has led to detritus of water quality and its unsuitability for drinking owing to the occurrence of these harmful elements in water. Even though the high concentrations of PTEs in the studied water, these elements occurred in low mobility and toxicity species: Fe(OH) 3 , Mn 2+ , (HAsO 4 ) −2 , Cd 2+ , Cr 2 O 3 , Cu 2 O, CuO, and PbCO 3 . This reflects the importance of studying element species rather than total concentration. Even though the unsuitability of this water for drinking owing to high concentrations of some PTEs, all of the samples were found to be suitable for irrigation.

Globally, groundwater is a valuable natural resource that may be relied upon for irrigation and drinking needs. The main purpose of this study is to investigate the groundwater geochemistry in the West of El Qusiya, Assuit, Egypt. Groundwater suitability for irrigation has been estimated with some methods, for instance, electrical conductivity (EC), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Killey ratio (KR), magnesium hazard (MH), permeability index (PI), Piper trilinear diagram, and USSL diagram. The Piper diagram shows that the sodium and potassium (Na+K) kind dominates the water chemistry, followed by the mixed type. The principal coordinate analysis (PCoA), cluster analysis (CA), principal component analysis (PCA), and Pearson correlation matrix analysis (PCMA) statistical methods reveal that the physicochemical parameters of water collected from the Eocene and Pleistocene aquifers are produced from mixed origins. The geogenic origin reflects the lithologic impact of aquifers matrix and water interactions, in addition to anthropogenic sources caused by infiltration of secondary salts initiated due to fertilizers and agriculture water. These factors are the controller for groundwater’s ionic (Na+, Ca2+, Mg2+, K+, Cl−, SO42−, and HCO3−) variation in the area studied. Based on SAR, KR, and PI results, groundwater is acceptable for irrigation. Consistent with RSC, MH, and Na% results, approximately 50% of the groundwater samples are unsuitable for irrigation use.

East Minia is considered as one of the most promising areas for the establishment of numerous sustainable development projects. The Middle Eocene Limestone aquifer is the main water source needed for the establishment of these projects. Therefore, 32 collected samples from different wells and chemically analyzed to determine the suitability of that water for drinking and irrigation, as well as mentioned to the various factors controlling the water quality through the application of hydrochemical diagrams and statistical analysis. TDS value of the studied water samples was ranged from 271 to 2328 ppm which indicates that nearby is 93.8% of the investigated water samples are acceptable for drinking uses, while total hardness value ranged from 32.19 to 1035.44 which indicates that there is 93.8% of the studied groundwater samples are suitable for domestic uses. Statistical analyses, Gibbs and End-member diagrams indicate that the water-rock interactions, geochemical process (Redox), besides anthropogenic activities are the essential contributor to the investigated groundwater chemical composition. Thus, the studied water is suitable for irrigation purposes based on the calculated sodium hazards and salinity.

Groundwater contamination by heavy metals is a worldwide serious issue due to its severe risks to human health. In the present study, a total of 49 groundwater samples were collected and analyzed for eleven trace elements (Al, Cr, Cd, As, Zn, Se, Sn, Ni, Pb, Mn, and Cu) in the west of Minia area, Egypt, to determine groundwater contamination by heavy metals and their impact on groundwater use for drinking and human health as a result. Multivariate statistics, geospatial mapping, and health risk assessment approaches are used to evaluate the potential non-carcinogenic and carcinogenic hazards in the research area and determine both natural and anthropogenic consequences of identified trace elements on local groundwater quality. The heavy metal concentrations (in mu g/l) in the groundwater samples were found to be in the following order: Zn (154.5) > Al (40) > As (37.4) > Sn (32) > Cr (28.4) > Hg (25.6) > Cu (21.8) > Cd (16) > Ni (15.4) > Pb (6.5). Heavy metals measurements revealed that As, Hg, and Cu do not meet WHO Guidelines Values, indicating a risk to human health from the consumption of groundwater. Zn > Al > As > Sn > Cr > Hg > Cu > Se > Cd > Ni > Pb was shown to be the order of the mean values of chronic daily heavy metal consumption for new-borns, children, and adults. Continuous oral intake of groundwater loaded with heavy metals could result in carcinogenic and non-carcinogenic concerns, posing serious health dangers to people throughout the life course.

The El-Minia district is a location of interest for future urban development. Using hydrochemistry and electrical resistivity studies, this work aimed to evaluate the groundwater potentiality and it's suitable for various uses. The groundwater potential in the study area was evaluated based on 24 VESs (vertical electrical soundings), and its quality was determined based on the analyses of 57 groundwater samples. EC (salinity index), Na% (salt hazard), SAR (ratio of sodium adsorption), chloride risks, SSP (soluble sodium percentage), MH (magnesium hazard), and other indicators were used to determine whether the collected water samples were suitable for irrigation. Four layers in the study area are mentioned in the geoelectrical cross-sections that have been constructed. The first is made up of silt and clay from the Nile River, while the second is made up of sandy clay, which has a resistivity range of 15 to 32 Ohm.m and a range thickness of 2 to 68 m. Dry limestone makes up the third layer; its resistivity ranges from 1222 to 3000 Ohm.m and its thickness varies between 75 and 95 m. The Eocene aquifer in the research area is represented by the final layer, which has a thickness of more than 250 m and resistivity values that range from 602 to 860 Ohm.m. Most groundwater samples that were collected are safe for drinking; however, none of them are fit for home usage because of their extreme hardness. According to the SAR and US diagram, RSC, KR, and PI, most groundwater samples from the Pleistocene and Eocene aquifers are fit for irrigation.

Egypt observes one of the highest water budget deficits in Africa that is mainly compensated by intensive reuse of untreated agricultural drainage water in the Nile Delta. The implications of untreated water reuse on increasing soil pollution levels remain poorly characterized; however, a large-scale pollution can compromise crop production and water quality. To address this deficiency, we evaluate the level of heavy metal pollution in the Nile Delta, identify its sources and explore the implications of damming on heavy metal concentration using integrated pollution indicators and statistical modeling. Pollution indicators show moderate to very high contamination by Pb, Ni, Cr, Cd, Cu, and Zn, with unprecedented Cd levels in the sediments (up to 72.0 ppm) and a northward increase in pollution levels. Statistical modeling and historical datasets reveal the association of Cd and Fe on both Nile branches and the clustering of Pb, Ni, Cu, Zn and Cr, which attribute the heavy metal concentrations to the cumulative addition of untreated agricultural drainage water (9.5 BCM/yr) and wastewater. These processes introduced an accelerated pollution in the Nile Delta system. Though, conservation measures are crucial to reverse this degradation, yet the increasingly engineered Nile flow, the low gradient of the delta and the active silting impede heavy metal flushing causing irreversible pollution. Our findings alarm future increase in heavy metal pollution in response to increased untreated drainage water reuse to mitigate the impacts of ongoing upstream damming and call for implementing international cooperative agreements for integrated water management along the Nile River.

The primary goal of this study is to analyze the hydrogeochemical properties and assess the groundwater quality for drinking, domestic, and irrigation purposes in West El Minia, Egypt. Major components were determined in 49 groundwater samples to evaluate water quality in the study area. Principal component analysis (PCA), hierarchical cluster analysis (HCA), geostatistics, and spatial mapping were used to identify the chemical components and processes that influence groundwater quality and highlight areas of health risks. According to the TDS values, about 22% of the groundwater samples are suitable for drinking. Due to the elevated values of hardness in the examined water, none of the water samples are suitable for use in a household. The majority of groundwater samples are acceptable for irrigation based on the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Kelley ratio (KR), magnesium hazard (MH), and permeability index, and some can be adequately treated. The study indicated that different groundwater characteristics (such as TDS, Na+, K+, HCO3−, Cl−, and SO42−) do not comply with WHO requirements in some regions, which may pose a threat to human health.

The groundwater of the west Assiut and El-Minia districts was evaluated in this paper using geoelectrical, hydrogeochemical, and stable isotope (oxygen-18 and deuterium) studies. In the studied localities, 42 vertical electrical soundings (VES) were taken to evaluate groundwater potential, and the analysis, as well as collection, of 74 samples of Eocene groundwater was carried out. In accordance with the vertical electrical soundings' interpretation, there are four geoelectrical formations and two major water-bearing units that act as aquifers (Pleistocene and Eocene). To determine irrigation suitability, the sodium absorption ratio (SAR), electrical conductivity (EC), residual sodium carbonate (RSC), sodium percentage (Na %), magnesium hazard (MH), Kelley's ratio (KR), and permeability index (PI) were evaluated as irrigation quality parameters. The EC, Na %, and the diagram of the US salinity laboratory indicated that most of the collected samples of groundwater were suitable for irrigation, whereas the RSC and PI pointed out that all of the collected water samples were safe for irrigation. The oxygen and hydrogen isotope values in groundwater samples showed that the Eocene aquifer was recharged by both surface water and the Nubian aquifer.

Shallow aquifer mapping and large-scale characterization of groundwater dynamics in the Saharan-Arabian Desert is largely impeded by the limited hydrological datasets from sparse and unevenly distributed well logs. Today, as these aquifers are depleting at alarming rates in response to climatic and anthropogenic stresses, accurate knowledge of their dynamical characteristics is not only essential for understanding the water deficit in these increasingly populated areas but also to understand the regional and global environmental impacts of such changes. Herein, we suggest that groundwater mounding can be used for assessing aquifer connectivity in hyper-arid deserts. Using the shallow Post Nubian Aquifer System (PNAS) in Egypt as a test site, we integrate remote sensing, isotopic, hydrochemical and geoelectrical methods to characterize the Saharan groundwater mounds, examine the structural control on groundwater dynamics and discuss the potential of future satellite missions to characterize aquifer connectivity. The results suggest that groundwater mounding in the PNAS is attributed to artesian discharge of the deep Nubian Aquifer System (NAS) along the intersection of WNW and E-W major faults. This is evident by the dominant isotopic signature (delta O-18: -9.93 parts per thousand; delta H-2: -79.05) of the deep NAS in the shallow PNAS with a percentage of up to 85% in the faulted zone. The 2D-Electrical Restively Imaging (ERI) delineate multiple small-scale mounds, atop of faults, that can attain 37 m height above average water table creating a relatively steep hydraulic gradient and deviating the groundwater flow direction. Future orbital radar sounding missions can benefit from characterizing the geometry of these mounds to define the measurement requirements of such hydrological features. The large-scale time-coherent subsurface mapping of the Saharan Arabian aquifers can provide unique insights to examine the aquifer connectivity and the response of aquifers to climatic and anthropogenic stresses in desert areas that otherwise cannot be addressed using existing sporadic well-logs. (C) 2021 Elsevier B.V. All rights reserved.