Water shortage and quality are major issues in many places, particularly arid and semi-arid regions such as Makkah Al-Mukarramah province, Saudi Arabia. The current work was conducted to examine the geochemical mechanisms influencing the chemistry of groundwater and assess groundwater resources through several water quality indices (WQIs), GIS methods, and the partial least squares regression model (PLSR). For that, 59 groundwater wells were tested for different physical and chemical parameters using conventional analytical procedures. The results showed that the average content of ions was as follows: Na⁺ > Ca²⁺ > Mg ²⁺ > K⁺ and Cl⁻ > SO₄²⁻ > HCO₃²⁻ > NO₃⁻ > CO₃⁻. Under the stress of evaporation and saltwater intrusion associated with the reverse ion exchange process, the predominant hydrochemical facies were Ca-HCO₃, Na-Cl, mixed Ca-Mg-Cl-SO₄, and Na-Ca-HCO₃. The drinking water quality index (DWQI) has indicated that only 5% of the wells were categorized under good to excellent for drinking while the majority (95%) were poor to unsuitable for drinking, and required appropriate treatment. Furthermore, the irrigation water quality index (IWQI) has indicated that 45.5% of the wells were classified under high to severe restriction for agriculture, and can be utilized only for high salt tolerant plants. The majority (54.5%) were deemed moderate to no restriction for irrigation, with no toxicity concern for most plants. Agriculture indicators such as total dissolved solids (TDS), potential salinity (PS), sodium absorption ratio (SAR), and residual sodium carbonate (RSC) had mean values of 2572.30, 33.32, 4.84, and −21.14, respectively. However, the quality of the groundwater in the study area improves with increased rainfall and thus recharging the Quaternary aquifer. The PLSR models, which are based on physicochemical characteristics, have been shown to be the most efficient as alternative techniques for determining the six WQIs. For instance, the PLSR models of all IWQs had determination coefficients values of R² ranging between 0.848 and 0.999 in the Cal., and between 0.848 and 0.999 in the Val. datasets, and had model accuracy varying from 0.824 to 0.999 in the Cal., and from 0.817 to 0.989 in the Val. datasets. In conclusion, the combination of physicochemical parameters, WQIs, and multivariate modeling with statistical analysis and GIS tools is a successful and adaptable methodology that provides a comprehensive picture of groundwater quality and governing mechanisms.

Evaluating grouLindwater quality and associated hydrochemical properties is critical to manage groundwater resources in arid and semiarid environments. The current study examined groundwater quality and appropriateness for agriculture in the alluvial aquifer of Makkah Al-Mukarramah Province, Saudi Arabia, utilizing several irrigation water quality indices (IWQIs) such as irrigation water quality index (IWQI), total dissolved solids (TDS), sodium adsorption ratio (SAR), potential salinity (PS), magnesium hazard (MH), and residual sodium carbonate (RSC) assisted by multivariate modeling and GIS tools. One hundred fourteen groundwater wells were evaluated utilizing several physicochemical parameters, which indicating that the primary cation and anion concentrations were as follows: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺, and Cl⁻ > SO₄^2˗ > HCO₃^˗ > NO₃^˗ > CO₃^2˗, respectively, reflecting Ca–HCO₃, Na–Cl, and mixed Ca–Mg–Cl–SO₄ water facies under the stress of evaporation, saltwater intrusion, and reverse ion exchange processes. The IWQI, TDS, SAR, PS, MH, and RSC across two studied regions had mean values of 64.86, 2028.53, 4.98, 26.18, 38.70, and − 14.77, respectively. For example, the computed IWQI model indicated that approximately 31% of samples fell into the no restriction range, implying that salinity tolerance crops should be avoided, while approximately 33% of samples fell into the low to moderate restriction range, and approximately 36% of samples fell into the high to severe restriction range for irrigation, implying that moderate to high salt sensitivity crops should be irrigated in loose soil with no compacted layers. The partial least squares regression model (PLSR) produced a more accurate assessment of six IWQIs based on values of R² and slope. In Val. datasets, the PLSR model generated strong estimates for six IWQIs with R² varied from 0.72 to 1.00. There was a good slope value of the linear relationship between measured and predicted for each parameter and the highest slope value (1.00) was shown with RSC. In the PLSR models of six IWQIs, there were no overfitting or underfitting between the measuring, calibrating, and validating datasets. In conclusion, the combination of physicochemical characteristics, WQIs, PLSR, and GIS tools to assess groundwater suitability for irrigation and their regulating variables is beneficial and provides a clear picture of water quality.

Combining hydrogeochemical characterization and a hyperspectral reflectance measurement can provide knowledge for groundwater security under different conditions. In this study, comprehensive examinations of 173 groundwater samples were carried out in Makkah Al-Mukarramah Province, Saudi Arabia. Physicochemical parameters, water quality indices (WQIs), and spectral reflectance indices (SRIs) were combined to investigate water quality and controlling factors using multivariate modeling techniques, such as partial least-square regression (PLSR) and principal component regression (PCR). To measure water quality status, the drinking water quality index (DWQI), total dissolved solids (TDS), heavy metal index (HPI), contamination degree (C_d), and pollution index (PI) were calculated. Standard analytical methods were used to assess nineteen physicochemical parameters. The typical values of ions and metals were as follows: Na²⁺ > Ca²⁺ > Mg²⁺ > K⁺, Cl⁻ > SO₄²⁻ > HCO₃⁻ > NO₃⁻ > CO₃²⁻; and Cu > Fe > Al > Zn > Mn > Ni, respectively. The hydrogeochemical characteristics of the examined groundwater samples revealed that Ca-HCO₃, Na-Cl, mixed Ca-Mg-Cl-SO₄, and Na-Ca-HCO₃ were the main mechanisms governing groundwater chemistry and quality under the load of seawater intrusion, weathering, and water-rock interaction. According to the WQIs results, the DWQI values revealed that 2.5% of groundwater samples were categorized as excellent, 18.0% as good, 28.0% as poor, 21.5% as extremely poor, and 30.0% as unfit for drinking. The HPI and C_d values revealed that all groundwater samples had a low degree of contamination and better quality. Furthermore, the PI values showed that the groundwater resources were not affected by metals but were slightly affected by Mn in Wadi Fatimah due to rock–water interaction. Linear regression models demonstrated the significant relationships for the majority of SRIs paired with DWQI (R varied from −0.40 to 0. 75), and with TDS (R varied from 0.46 to 0.74) for the studied wadies. In general, the PLSR and PCR models provide better estimations for DWQI and TDS than the individual SRI. In conclusion, the grouping of WQIs, SRIs, PLSR, PCR, and GIS tools provides a clear image of groundwater suitability for drinking and its controlling elements.

Influences of land use and monsoon recharge on groundwater geochemistry in the hard rock aquifer in south India are studied using geochemical modelling, geochemical and geospatial tools, and Pearson correlation analysis (PCA). Groundwater samples were collected from 2017 to 2019 (n = 267) and analysed for EC, pH, major ions, and minor ions. Water samples were classified into urban (n = 89) and agricultural (n = 178) regions based on land use patterns. Groundwater is very hard (Total Hardness > 180 mg/l; 74%), and the predominant water types are Ca–Mg–Cl followed by Na-Cl. In the agricultural region, groundwater is less mineralized (TDS < 500 mg/l; 62%) compared to urban regions (38%). In the urban wells, ionic strength and Log pCO₂ justified the wastewater infiltration. The groundwater is undersaturated with halite, gypsum, anhydrite and fluorite and saturated/supersaturated with carbonate minerals. PCA and geochemical tools indicate that water chemistry is predominantly governed by silicate weathering and ion exchange reactions. The interconnection between Cl⁻, SO₄²⁻ and NO₃⁻ ensures the impact of nitrification/nitrate sources along with anthropogenic input. In 2018, Cl⁻ and NO₃⁻ contents were reduced by dilution due to high rainfall (2061 mm), whereas HCO₃⁻ was enriched owing to recharge-induced mineral dissolution. Geospatial tools explain that the groundwater quality was improved in 2018 and justified by NO₃⁻ (< 45 mg/l; 3291 to 4138 km²; > 100 mg/l; 176 to 9 km²), Cl (< 200 mg/l, 1975 to 2747km²) and HCO₃⁻ distributions. The outcome of this study highlights that urban wells are highly polluted and need proper management practices to protect this hard rock aquifer.

A flash flood is one of the hazardous phenomena, especially in dry regions. In Saudi Arabia, Jazan Province experiences data scarcity especially historical hydrological data and a lack of studies related to flash flood analysis and the rainfall and runoff interrelationship. Thus, this research aims to study the rainfall-runoff inter-relation, predict flash floods, and to map the risk areas in Jazan Province by the geological, geomorphological, and hydrogeological characteristics along with digital elevation model (DEM), watershed modeling system (WMS) and HEC-HMS models. Jazan Province encompasses 25 drainage basins, receiving a considerable amount of rainfall (ranging from 100 to 500 mm) (August, October-November, March) which intermittently cause strong and destructive flash floods. The DEM was used for delineating the catchment (drainage basins) parameters. Physiographic parameters of the catchments have been analyzed for mapping the hazard degree of the flash flood strength. Further, basins with high hazard degrees of flash floods were selected to assess rainfall-runoff inter-relation using the HEC-HMS models, GIS, and morphometric parameters. Forty %, 8%, 52% of the study area are high, medium, and low hazard degrees of flash floods, respectively. The groundwater recharge in the study area was calculated through the integration of satellite image analysis, SWAT and GIS techniques and it ranges from 0.002 mm/km²/year to 8 mm/km²/year with an average of 2.5 mm/km²/year. Rainfall-runoff inter-relation of study basins, assessed based on the integration of WMS and HEC-HMS models, indicates that the resulting runoff volume ranges from 18.5 × 10⁶ m³ to 473.1 × 10⁶ m³ at a recurrence period of 5 and 100 years at rainfall events of 65 mm and 116.8 mm, respectively.

Trace metals pollution in the freshwater system is an emerging concern. Thus, a systematic study was performed in the Wadi Fatimah basin to appraise the trace metals pollution status, sources and associated health risks using integrated tools, namely indices, international standards, multivariate statistical techniques and health risk assessment models. The groundwater salinity shows a wide range (TDS = 391 to 11,240 mg/l). The heavy metal pollution index and contamination index justify that most of the samples are unfit for drinking due to high metal pollution. Severe pollution is noticed by the Li (100%), Ni (98%), Pb (86%) and B (78%), and it is in the decreasing order of Mo > Cr > Al > Fe = Mn > V > Sr > Ag > Cu. Pearson correlation matrix suggests that most of the metals have a significant strong positive correlation with Al, Fe and Mn and originated from geogenic sources. Principal components analysis and R-mode HCA indicate that trace metals are mostly derived from weathering of aluminium silicates, oxides/hydroxides of Fe and Mn followed by evaporation, evaporite dissolution and restricted flow. Q-mode HCA resulted in 4 clusters, and the water chemistry of WG1 and WG4 is governed by mineral weathering. In addition, evaporation also enriched the metal load and salinity in WG4 wells. In WG2, the water chemistry is predominantly affected by long storage, evaporation and mineral weathering. In WG3, the water chemistry is influenced by evaporation, irrigation return flow and evaporite dissolution. The hazard quotient and hazard index suggest that groundwater in this basin causes potential non-carcinogenic health risks to the consumer. This study strongly recommends treatment for groundwater before supply to the local inhabitants.