**2. Study Area**

The case study area of this research is Islamabad, the capital city of Pakistan, located at the edge of the Potohar plateau. It is located 14 km northeast of Rawalpindi in the

province of Punjab. In terms of map reference, it is located at 33◦490 north and 72◦240 east of Greenwich [74,75]. Islamabad lies at an altitude range of 457–610 m and has 906.50 km<sup>2</sup> [76]. The climate of the area is humid and subtropical. May, June, and July are the warmest months, with average temperatures ranging from 36 ◦C to 42 ◦C, with temperatures sometimes as high as 48 ◦C. In comparison, the coldest months are December and January, with mean minimum temperatures ranging from 3 ◦C to 5.5 ◦C [77].

In Islamabad, groundwater is mainly used for drinking and agriculture purposes [78]. Since its announcement as the capital on 14 August 1967, the urbanization in and around Islamabad has been growing rapidly, leading to the development of multiple residential sectors (Sectors D to I) and more new ones being proposed, such as sectors A to C and sub-sectors I-14 to I-16 [74]. This is due to the increased migration of people in hopes of better facilities and high-end, luxurious lifestyles. According to the 2017 census, Islamabad recorded a population growth rate of 4.91 percent, and its population increased from 0.81 million in 1998 to 2.0 million in 2017 [79]. Such a mass-level migration to Islamabad increases the demand and reliance on groundwater to sustain life necessities [80].

Moreover, since Islamabad rests on the Potohar Plateau and consists of a hard rock terrain, its surface does not allow enough permeable surface for groundwater tables to be properly recharged [70]. As a result, the groundwater levels of Islamabad are depleting rapidly on an annual basis, as reported by the metropolitan corporation of Islamabad [80]. The Interior Ministry of Pakistan reported a 6 ft decrease in Islamabad groundwater in 2013, followed by a 10 ft, 16 ft, 23 ft, and 30ft from 2014 to 2017, respectively. It is estimated that groundwater levels in Islamabad have decreased by five times as of 2018 [80]. Therefore, it is imperative that new and reliable water sources must be found. Accordingly, it is necessary to carry out a study to delineate the potential groundwater zones in the city. This can help the policymakers and town planners to preserve such zones with permeable strata in the city to mitigate this groundwater recharge issue or alternatively better plan the construction activities around such areas.

Figure 1 shows the Islamabad map that is divided into five zones: zone 1 to zone 5 [74]. These zones are the administrative boundaries of the study area. They can be used as a reference for policymakers for decision making for each zone with respect to findings of this research. The city infrastructure has been planned in nine sectors in total, and an alphabet from A–I represents each sector. Every sector covers an area of approximately 2 km<sup>2</sup> and is further subdivided into four sub-sectors, each containing a central shopping mall, public park, and other amenities [74,81]. These sectors are the gridded divisions of the city to subdivide the capital into small units. It is similar to municipalities in developed countries and presents a grid division of the city. Out of the 5, zone 4 has the largest area, 282.5 km<sup>2</sup> [82], while zone 1 has the most developed residential area [83]. Zone 2 has an area of 9804 acres. Since CDA apportioned this zone to a private and cooperative housing scheme for improvement, zone 2 has become the city's most alluring space [83]. Zone 3 (203.9 km<sup>2</sup> ) is one of the most beautiful areas of Islamabad. Vacation spots such as Daman-e-Koh and Peer Sohawa are situated in this zone [84]. Zone 5 (157.9 km<sup>2</sup> ) is near the old airport and is one of the most populated zones [85].

Islamabad continues to experience expansion to accommodate the increasing population. The territorial limits of Islamabad have expanded by 87.31 km<sup>2</sup> from 1972 to 2009, with a significant reduction in the forest covers and other natural habitats [86]. As a result, Islamabad has registered the highest population growth rate of 4.91 percent, and the population has increased from 0.81 million in 1998 to 2.0 million in 2017 [79]. This rapid urbanization has led to many development projects being initiated within the city, including the extension of transportation systems, revision of the city master plan, and industrial and real estate development [12,75] that provide job opportunities to the residents [87,88].

**Figure 1.** The study area (Islamabad) and its zones. **Figure 1.** The study area (Islamabad) and its zones.

Islamabad continues to experience expansion to accommodate the increasing popu‐ lation. The territorial limits of Islamabad have expanded by 87.31 km2 from 1972 to 2009, with a significant reduction in the forest covers and other natural habitats [86]. As a result, Islamabad has registered the highest population growth rate of 4.91 percent, and the pop‐ ulation has increased from 0.81 million in 1998 to 2.0 million in 2017 [79]. This rapid ur‐ banization has led to many development projects being initiated within the city, including the extension of transportation systems, revision of the city master plan, and industrial and real estate development [12,75] that provide job opportunities to the residents [87,88]. Due to this rapid increase in population, Islamabad has undergone many predicted and unpredictable changes [74]. One such change is the higher water demand in the re‐ Due to this rapid increase in population, Islamabad has undergone many predicted and unpredictable changes [74]. One such change is the higher water demand in the region [80]. The main water resources for Islamabad are surface- and groundwater. Simli Dam and Khanpur Dam are major water resources for Islamabad. Along with the surface water, the Capital Development Authority (CDA) supplies groundwater extracted from 180 tube wells to Islamabad. Private and municipal wells are also used to fulfill the local water requirements [79]. Despite the aforementioned resources, the increased population has heightened the reliance on groundwater since it is one of the primary sources for domestic use [89]. The resulting extensive use of groundwater in the region leads to the depletion of natural groundwater resources [80].

gion [80]. The main water resources for Islamabad are surface‐ and groundwater. Simli Dam and Khanpur Dam are major water resources for Islamabad. Along with the surface water, the Capital Development Authority (CDA) supplies groundwater extracted from 180 tube wells to Islamabad. Private and municipal wells are also used to fulfill the local water requirements [79]. Despite the aforementioned resources, the increased population has heightened the reliance on groundwater since it is one of the primary sources for do‐ mestic use [89]. The resulting extensive use of groundwater in the region leads to the de‐ pletion of natural groundwater resources [80]. Moreover, considering that the study area is situated in the Potohar Plateau, where the terrain is geologically composed of tertiary sandstone, limestone, and alluvial deposits [77], the recharge capacity of the region is not good. Thus, groundwater does not recharge properly, resulting in the depletion and unavailability of clean drinking water. The areas Moreover, considering that the study area is situated in the Potohar Plateau, where the terrain is geologically composed of tertiary sandstone, limestone, and alluvial deposits [77], the recharge capacity of the region is not good. Thus, groundwater does not recharge properly, resulting in the depletion and unavailability of clean drinking water. The areas facing severe water shortage include sectors G6, G7, H8, G13, I-10, [90], and I-8/1 [91]. Thus, it is important to manage the regional groundwater resources [78]. For this purpose, the current study delineates Islamabad's potential groundwater recharge zones. The obtained potential recharge map provides the information to help improve the local management of groundwater resources. Such an assessment is important for future planning and development policies in the area and devising strategies for efficiently utilizing natural resources such as groundwater.

#### facing severe water shortage include sectors G6, G7, H8, G13, I‐10, [90], and I‐8/1 [91]. **3. Factors Affecting Groundwater Recharge Potential**

Groundwater is affected by multiple factors such as land use, slope, and lineament [92]. In addition, the study area's rainfall, soil conditions, and soil types also influence the

groundwater [93]. In this study, 15 influencing factors (Ifs) were identified and used to develop potential zones to produce an error-free diverse outcome instead of a single influencing factor outcome, which provides a limited outcome in terms of accuracy [65]. Broadly, these factors can be grouped into four key groups: (1) elevation and slope, (2) rainfall and drainage, (3) land-use/land-cover and soil characteristics, and (4) faults, as listed in Table 2. The influencing factors (IFs) are the factors that can affect some features of the target object, system, or phenomenon [94]. IFs can be used as control variables to determine the key influencing factors of an object, system, or phenomenon. These have been used in various studies. In water-related studies, IFs have been used to assess the seasonal changes in water quality [95], water transport through cracks in concrete [96], distribution characteristics of microplastics in urban tap water [97], comprehensive evaluation and urban agglomeration water resources carrying capacity [98], and others. Accordingly, in the current study, IFs are used to delineate potential groundwater recharge zones in Islamabad, Pakistan. These 15 key factors are listed in Table 2 and discussed subsequently.

**Table 2.** Factors influencing groundwater recharge classified criteria.

