*3.6. Rainfall*

Rainfall or precipitation positively affects the groundwater table because of larger water infiltration [93]. Rainfall has always been a reliable source of freshwater [65]. Previous research has linked both the movement and occurrence of ground and surface water to mainly depend upon rainfall [108,111]. Considering that the rainfall quantities of the study area can indicate the movement of groundwater and can depict the flow and accumulation of water bodies, it is important to include this factor while investigating groundwater recharge zones [109]. Therefore, it is considered significant for Islamabad as well and used in the current study as a key factor. Further, since Islamabad is a rainy area, and some mountainous regions in the area receive more rainfall than other parts of Pakistan, rainfall is a key factor dictating the local climate and recharging the water sources.

#### *3.7. Drainage Distance*

Drainage distance is crucial for water studies, such as its occurrence and flow assessments. Drainage distance highlights the geological distance between successful drainage zones. The drainage density indicates the drainage condition of the water shed [109]. Groundwater movement beneath the surface can be unfolded by uncovering the drainage networks according to lineaments such as underground fractures and faults. Lineaments impact groundwater movement within the surface [65,102]. For studies relating to groundwater recharge, the inclusion of drainage distance is crucial because of its relationship with permeability which is the property that describes the flow of water bodies beneath the earth's surface [108]. A similar study prioritized areas comprising more considerable drainage distances for the groundwater recharge potential and vice versa [109]. Accordingly, drainage distance has been shortlisted as a key factor in the current study for the study area of Islamabad.

#### *3.8. Drainage Density*

Drainage density is the ratio of all the streams over the area to the total area [65]. It indicates the drainage capacity and measures the drainage over a particular watershed [103]. A higher drainage density region indicates a well-distributed water flow area with multiple streams contributing to the flow and recharge and vice versa. A similar study has linked higher drainage density to greater groundwater recharge potential [108]. According to the previous research, the drainage density contributes toward the groundwater recharge as it describes the flow pattern and the occurrence of water beneath the surface [65,109]. As Islamabad receives higher rainfall towards the northern outskirts, and the density of the drainage network would greatly influence the flow and occurrence of groundwater in the region, drainage density is selected as a key factor for this study.
