Identification of suitable sites for rainwater and storm water harvesting through spatial analysis and smart sustainable urban water infrastructure in Lahore, Pakistan Open Access

There are many challenges to attain future water-wise, sustainable, and smart cities around the globe, especially in developing countries. Climate change is causing wider swings in weather. More intense and extreme weather events will be observed worldwide in the future, too (IPCC 2021). Pakistan lies within the area under the influence of the world's largest monsoon weather system. In Pakistan's history, disastrous flooding was caused by the unusually large rainfall from the 2010 and 2014 monsoon. Almost 20 million persons were affected. One-fifth of the country was flooded, taking away over 2,000 lives in 2010. Such events also revealed the country's vulnerability to flooding in economic terms. Pakistan's cities are vulnerable to urban flooding due to extreme climate change events and becoming water scarce at the same time due to prompt urbanization and population increase (World Bank report 2016). Rapid urbanization has engulfed open urban spaces and does not let the rainwater infiltrate properly. Excessive runoff creates urban flooding, which is always beyond the carrying capacity of the Lahore drainage system. Unsustainable water use and fragmented management place enormous pressure on surface and groundwater resources. The population of Lahore depends entirely on groundwater, which is more than 13 million, according to Sajjad et al. (2023). Water is abstracted through 585 tube wells to meet the population's needs. However, Lahore receives an average annual rainfall of about 715 mm (PMD 2020), which does not contribute much to recharging the aquifer, as groundwater discharging is much higher than recharging. The difference between the recharging and discharging rate of the Lahore aquifer is 327 million m³. As a result, the water table of Lahore is depleting at an alarming rate of 3.3 feet per annum (Siddiqui et al. 2018). According to the ‘Final Master Plan Report for Lahore 2040’, the Lahore aquifer has been facing an increasingly negative trend since the 1970s due to population growth, urbanization, and excessive pumping.

The Ravi River has low discharge, and the canal is almost dry in the winter, except in the monsoon season (July–August) every year, resulting in chances of further water table depletion (Qureshi & Sayed 2014; Cooper 2018). This is all due to the disturbance of the natural hydrological cycle. Strategic schemes for managing the urban water cycle must be formulated to achieve an eco-friendly hydrological cycle and build water-wise cities. The urban water model of China's Sponge City program has shown notable success (Liu 2016; Xia et al. 2017). Moreover, many countries worldwide have adopted effective strategies to address urban water management (UWM) challenges. They introduced their design for integrated urban water management (IUWM), like the active, beautiful, clean waters program (ABC) in Singapore (Lim & Lu 2016), low impact development (LID) in the USA (Xu et al. 2017), the low-impact urban design and development program (LIUDD) in New Zealand (Fletcher et al. 2015), and sustainable urban drainage systems (SUDS) in the UK (Ellis & Lundy 2016), and water-sensitive urban design (WSUD) in Australia (Liu 2016).

Cities could be transformed into water-wise cities by implementing better urban planning with modern technology such as GIS and R.S. Rainwater harvesting potential (RWHP) for any surface area can be calculated. Once the sites are identified, the decision-making process for suitable urban water infrastructure (UWI) becomes more straightforward, as it involves knowing the estimated potential for harvesting stormwater or rainwater. Furthermore, the World View Water Index (WV-WI) is designed to identify areas with standing water (Demarchi et al. 2020). Javid et al. (2021) used WV-WI to identify water bodies throughout Lahore and assess changes in the water surface area due to urbanization.

Lahore is situated within the Köppen climate classification of BSh (composite rainstorm atmosphere), placing it in a semi-arid zone. The city experiences five distinct seasons, including spring, summer, autumn, and winter, with the fifth season being the monsoon rainy season (Akbar et al. 2019; Javid et al. 2019). The monsoon season, characterized by heavy rainstorms, occurs from July to September. Lahore is administratively divided into nine towns and also includes a cantonment area (Siddiqui et al. 2018, 2020; Siddiqui & Siddiqui 2018).

Our spatial analysis was also conducted using the WV-WI in Equation (1). This index was selected as it best aligns with the study's objectives, utilizing WorldView-2 bands to identify areas with standing water exceeding one pixel in size.

To transform Lahore into a water-wise city, we draw on an extensive literature review of worldwide urban water systems, focusing on modern urban models such as Chinese Sponge cities. We examine how these models have successfully transitioned unnatural urban environments into nature-friendly ecosystems within a few years. We aim to understand how the collaboration of urban geographers, planners, hydrologists, landscape planners, responsible authorities, and political will can facilitate the urban water transformation of a city.

The identified suitable RSWHPS in urban areas serve as the basis for a step-by-step transformation of UWI. These sites are categorized into four classes: high, moderate, medium RSWHPS, and river or canal sites. The transformation process begins with the high-potential sites (HPS) and progresses accordingly.

Spatial analysis to identify RSWHPS was conducted using the WV-WI, as detailed in Equation (1) (Wolf 2012). The R.S. index of WV-WI was calculated using a raster calculator within a GIS environment, resulting in a geometric resolution of 10 m. Pixel values were computed using ArcMap software (Costantino et al. 2020). As a result, the analysis revealed a total potential area of 85.54 km² for rainwater and stormwater harvesting during the monsoon season. On included river and canal areas, this figure expands to 96.8 km² (Table 1).

As previously mentioned, this index is ideal for highlighting and identifying areas of standing water larger than one pixel. The potential sites are categorized into four classes based on their harvesting potential. HPS cover 17.48% (16.91 km²) of Lahore city, while medium-potential sites (MPS) account for 17.39% (16.83 km²), nearly equal to the high-potential area. The thematic map in Figure 3 indicates that most HPS are located in the city's Central Business District (CBD), making them a priority for treatment due to their more significant economic impact compared to other areas. The Lahore Central Business District Development Authority (LCBDDA) has been tasked with developing environmentally friendly urban regeneration projects following vertical principles, aiming to enhance the city's attributes through walkable urbanism and smart infrastructure. Low-potential sites (LPS) cover a larger area in Lahore, accounting for 53.5% (51.76 km²). These sites can be found throughout the city as puddles and shallow depressions, with a higher concentration in Wagha Town, Shalimar Town, and Ravi Town (Table 2).

LPS are typically located in newly developed areas or new urban towns, posing fewer immediate concerns but still requiring resolution for the well-being of residents. MPS cover an area of 16 km² and are primarily found in the historically developed Lahore regions, especially in the northern and eastern parts, with some pockets in newly developed areas. Harvesting this freshwater rather than allowing it to flow into the sewerage system is essential.

In Wagha town, which offers the largest available area for RSWHPS in Lahore, there are 5.36 km² of HPS, 6.01 km² of MPS, and 10.62 km² of LPS (see Table 3).

Iqbal town has the second highest potential site area with an area of 3.82 km² in HPS. Shalamar town ranks second in MPS with an area of 3 km². For LPS, Shalamar town also ranks second. Ravi town comes in third place with 2.88 km² in HPS. Iqbal town has the highest area for MPS at 1.94 km², while Ravi town has 7.83 km² in LPS.

The towns with the smallest RSWHPS areas are Aziz Bhatti town, with 0.25 km² in HPS, Samanabad town with 0.37 km², and Gulberg town with 0.47 km² HPS (Table 3).

In contrast, the cantonment area has limited potential sites, with 0.25 km² in HPS, 1.31 km² in MPS, and 7.83 km² in LPS. This is due to ample budget allocation for development and strict administration by the army, which enforces rules for implementation. Open green spaces are available in residential and commercial areas, allowing rainwater to infiltrate the groundwater. In other towns, especially Wagha and Ravi town, open spaces are insufficient for groundwater recharge, and these areas lack technical planning and administrative oversight.

Sustainable and water-wise cities are essential to accommodate rapidly urbanizing populations worldwide. With the use of innovative technology and improved urban planning, cities can be transformed into water-wise cities (Rogers 1993). Once the potential sites are identified, we can estimate RWHP (Siddiqui et al. 2018, 2020; Siddiqui & Siddiqui 2018). This information is crucial for decision-making in UWI design.

A significant amount of fresh rainwater often becomes greywater without recharging our groundwater, leading to urban flooding during monsoon rains, exceeding our drainage system's capacity.

To address this, we recommend designing low-profile green belts and bioretention infrastructures for Lahore's urban water transformation. Bioretention facilities, also known as rain gardens, act like sponges and natural filters, allowing water to percolate slowly into the ground. These gardens are designed with a slight depression, size depending on expected rainwater entry. Native plants can be used to attract wildlife, maintaining the ecosystem. Small boulders or berms at the garden's edge help retain water during heavy downpours. The amended soil, composed of topsoil, sand, and compost, filters the remaining water, removing pollutants and supporting plant growth, creating a beautiful habitat for various fauna (Wang et al. 2018).

This is the best structure for recharging the aquifer of Lahore. Bioretention facilities do not promote the spread of dengue because rainwater remains temporary for less than 24 h. This short duration is insufficient for completing the mosquito breeding cycle, which typically takes 7–14 days. Therefore, it represents an effective mitigation strategy for addressing the depletion of Lahore's water table and ensuring safe UWI for clean water. These UWI designs should align with Lahore's identified suitable RSHPS. The primary objective should be to restore Lahore City's eco-friendly urban hydrological cycle.

It will improve a city's resilience to urban expansion and climate change by constructing a healthy urban water cycle system where ‘urban rainfalls can accumulate, infiltrate, and cleanse naturally’. Any future UWI transformation should be designed to obtain the objectives of infiltration of rainwater, detaining it, storing it, cleansing it before use, and draining it in grey water.

The spatial analysis identified potential sites in Lahore's towns, classifying them into four categories. The highest potential site area covers 16.91 km². When a ground survey was conducted, the results confirmed the identified RSWHPS using the WV-W index. This study proposes city transformation through innovative urban water infrastructure (IUWI) technologies to create sustainable, water-wise cities. Consequently, this study provides valuable insights for policymakers to simultaneously address water scarcity and urban flooding. Understanding potential harvesting sites is crucial for future UWI planning in Lahore and beyond, guiding the development of innovative and sustainable systems for environmental enhancement in urban areas. This research serves as a data-driven blueprint for the future transformation of Lahore's UWI, with potential applications in other cities across Pakistan.

No funding was obtained for this study.

All the authors have proofread the manuscript, participated, and approved for submission.

R.S. wrote the main manuscript, K.J. reviewed and modified the manuscript, and M.I.A. supervised the study. All the authors proofread carefully and approved for submission.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.