In arid climates, conventional water resources are severely limited and stressed in the face of rapid population growth and future climate change. So, it is necessary to find alternative non-conventional water resources for use in drought situations. Additionally, the non-conventional water resources in these areas are not sufficient to meet future water demand. Therefore, non-conventional water resources can be adopted as a strategic reserve to bridge the gap between water supply and demand in case of emergency and drought events. These resources might include rainwater harvesting, treated wastewater, and desalinated seawater. Managed aquifer recharge (MAR) can be applied to store these resources in the hydrogeological system using Geo information System—Multi Criteria Decision Analysis (GIS-MCDA) approach for determining the suitable MAR location for storage. North-west Kingdom of Saudi Arabia area was chosen for this study because it is extremely arid, has high potential for social and economic development, and it has newly constructed non-conventional water infrastructures distributed throughout the area including water desalination plants, Tertiary Sewage Effluent (TSE) waste water plants, and flash-flood storage dams. To identify the suitable MAR site location and structure, different data related to aquifer hydrogeology, surface hydrology, hydrometeorology, and water quality were applied. Then, GIS-MCDA holistic approach was applied with aid of ordered weighting average (OWA) technique. Finally, two maps were created to show the MAR location and structure type. Potential map indicates that ~ 18.85% of the area is suitable for MAR installations. About 0.17% of the total area exhibited very high potential, where infiltration ponds can be applied, 1.86% had high potential for construction of check dams with diversion channels, and 16.82% had moderate potential for installation of recharge wells. Additionally, 56 MAR structures were proposed and a map showing their locations has been created. Thus, results indicated that the study area is promising for MAR installation. These maps could aid the decision makers to propose a sustainable development plan for the future water resources of the area.

Studying and determining the physical properties and hydraulic parameters of vadose zone sediments is an important key to evaluate the infiltration rate into them and assessing the extent to which aquifer sediments benefit from rainwater harvesting in arid and semi-arid areas. Due to the lack of sufficient data on the characteristics of this zone depths, a numerical modeling was used to simulate the electrical resistivity of these sediments by applying the electrical resistivity method, because it is the most affected by the physical properties of dry and wet sediments. This study was applied as a proposal for application in northwestern KSA to calculate the vertical hydraulic conductivity and transmissivity for the vadose zone. This was implemented by assuming a three-layer model using COMSOL Multiphysics model with different electrical resistivity values depending on some in situ electrical resistivity measurements for shallow depths. Hence, the infiltration rate of sediments in this area can be predicted with depth and its effect on aquifer recharge. The focus was on calculating the vertical hydraulic parameters of the most widespread surface sediments with depth and comparing the results of calculating these parameters for some sediments laboratory-wise to ensure their accuracy. Then, their infiltration rate was inferred separately with depth, predicting their ability to aquifer recharge and make the most of rainwater harvesting. Finally, this study can be considered as a preliminary study to determine the expected forward model of electrical resistivity and hydraulic parameters values for the vadose zone sediments with depth along the area and in any other areas, and then apply them accurately in situ to estimate the extent of its usefulness in rainwater harvesting, especially aquifer recharge.

In the last few decades, groundwater has been the main water supply to the Nuweiba alluvial fan. However, currently, the main water supply is a desalination plant. The desalination plant might be vulnerable to malfunctions resulting in a severe drought. In addition, the aquifer type in the fan is coastal. Hence, replenishing the groundwater is necessary on a long-term basis to overcome drought events in the case of emergency. To replenish the groundwater using flash-flood water, a Managed Aquifer Recharge (MAR) system could be installed. This study applies the Geo-Information System–Multi-Criteria Decision Analysis (GIS-MCDA) method to delineate the feasible locations for installing a MAR system. To delineate the feasible MAR sites via a potential map, four steps were performed: problem definition, constraint mapping, suitability mapping, and sensitivity analysis. The results show that nearly 52% of the study area is suitable for installing MAR. Additionally, around 6% of the study area shows high potential for installing MAR, whereas nearly 20% falls under the moderate potential class. The potential map shows that the high-potential MAR sites are located at the western portion of the study area, near the ephemeral stream outlet. The map could be utilized as a tool for decision-makers to plan a future sustainable development strategy.

Groundwater is the main water source in arid climate regions. Climate change and extensive groundwater exploitation will stress the groundwater resources in the upcoming decades. Therefore, groundwater quantity and quality should be assessed. In this study, we focused on groundwater quantity, including recharge and storage (using groundwater level as an indicator) to predict system vulnerability. The northern portion of El-Qaa Plain was chosen as a case study because the aquifer is coastal, arid, over-exploited, and naturally replenished via seasonal precipitation events. To project groundwater recharge under climate change and future exploitation, Water and Energy Transfer between Soil, Plants, and Atmosphere under quasi-steady State (WetSpass) was applied. Modular Finite Difference Groundwater Flow Model (MODFLOW) was utilized to project the groundwater level. Future climate ensembles were acquired from Regional Climate Models (RCMs) of Coordinated Regional Downscaling Experiment (CORDEX) datasets for the EURO 11 domain. The ensembles were bias-corrected using the Delta Change Factor (DCF) method. The results indicate that groundwater resources will be severely affected by climate change, as recharge might drop by nearly 35% to 75% during 2071–2100 for moderate and severe change ensembles. The mean groundwater level might decline by around 7–8 m by 2100 for the same ensembles. Regarding over-exploitation, the maximum drawdown will rise to approximately 16 m (no change in abstraction rate), to 36 m (increase in abstraction rate), and 7 m (decrease in abstraction rate). The results might aid decision-makers and stakeholders developing sustainable water resource management plans for the area.

Hydrogeological parameters are very uncertain to specify in the groundwater flow models. Hence, it is important to specify a range for these parameters to be further utilized by the groundwater model users. In El-Qaa Plain, previous researchers have determined the hydrogeological parameters such as transmissivity, hydraulic conductivity, and mean annual recharge rate using geophysical methods, pumping tests, hydrological models, and groundwater flow models. However, they are also limited to specific locations and do not spatially distribute. In this paper, an effort has been accomplished to specify a specific range for the aquifer hydrogeological parameters using inverse groundwater modeling taking into account the spatial heterogeneity. These ranges could be taken into consideration during modeling groundwater flow. Hence, a finite-difference groundwater flow model has been applied using the ModFLOW model. Regularized pilot points method (RPPM) has been chosen as an inverse modeling technique to specify the accurate values of the aquifer parameters. Model-independent parameter estimation and uncertainty analysis (PEST) has been utilized to estimate the parameters. The results show that the geometric mean of the hydraulic conductivity in the study area ranges from proximity 1 to 2 m/day. Additionally, the geometric mean of the transmissivity ranges from nearly 200 to 500 m²/day. A relationship between the mean annual recharge rate and hydrogeological parameters has been determined. Besides, maps have been generated showing the spatial heterogeneity of the hydraulic conductivity. These maps could be further utilized by groundwater flow modelers to predict the potential of groundwater flow and pollution in the future.