Assessment of groundwater depletion rate by numerical modelling: a case study of Johar town Lahore, Pakistan

In the bustling cities of South Asia, a quiet crisis is unfolding beneath the streets. Groundwater, the vast reservoir of fresh water hidden underground, is being pulled out faster than nature can refill it. This hidden resource is not an endless well; it is a bank account where the withdrawals are outpacing the deposits. When rain falls, it soaks into the soil and slowly trickles down to replenish these underground layers, a process known as recharge. However, as cities expand, concrete and asphalt cover the ground, blocking the rain from reaching the aquifer below. At the same time, growing populations and industries pump out water at an accelerating rate. When the balance tips, the water table drops, forcing people to dig deeper wells, increasing costs, and risking the quality of the remaining water. Understanding exactly how fast this water is disappearing in specific neighborhoods is crucial for planning a future where cities do not run dry.

In the dense urban landscape of Johar Town, a neighborhood in Lahore, Pakistan, researchers have turned to a digital tool to measure this invisible decline. The team, led by Sonia Anwar, used a sophisticated computer program to create a virtual twin of the underground water system in this area. This software, known as Visual MODFLOW, acts like a detailed map that simulates how water moves through the soil and rock layers. To build this model, the researchers gathered real-world data from local authorities, including records of how much water was being pumped from wells, the depth of the water levels, and rainfall patterns over the last decade. They mapped out the location of every pumping station and the physical properties of the ground, such as how easily water can flow through the soil, a property called hydraulic conductivity. By feeding this information into the computer, they could watch how the water levels changed over time in the simulation, effectively running the history of the last six years in a digital environment to see what was really happening underground.

The results of this digital investigation revealed a clear and steady trend. Between 2015 and 2021, the groundwater level in Johar Town dropped by an average of nearly 0.88 meters every year. Over the course of those six years, the total water table fell by more than two meters. This decline is not just a number on a chart; it represents a tangible shift in the environment. As the water recedes, the cost to extract it rises, and the water itself becomes more vulnerable to contamination from the surface. The researchers found that the primary driver of this drop is the rapid urbanization of the area. As farms and open fields are replaced by buildings and roads, the ground loses its ability to absorb rainwater. Instead of soaking into the earth to recharge the aquifer, the rain runs off the hard surfaces, leaving the underground reservoir empty. This problem is compounded by the sheer volume of water being pumped out to meet the needs of a growing population and its industries.

To ensure their findings were accurate, the researchers tested their model against real observations. They adjusted the settings in the computer simulation, particularly the value for how easily water moves through the soil, until the simulated water levels matched the actual measurements taken from wells in the field. They found that the speed at which water moves through the ground was the most critical factor in determining the water levels. Once the model was tuned to match reality, it confirmed that the depletion rate was consistent and significant. The study also highlighted that while rainfall does help refill the aquifer, the amount of rain falling in the region is not enough to counteract the massive amount of water being removed. Even in years with heavy rainfall, the net effect was still a loss of water from the underground system.

The implications of these findings extend beyond a single neighborhood. The study suggests that the current way of managing water in Lahore is unsustainable. The researchers propose that simply waiting for rain is no longer a viable strategy. Instead, they recommend a shift in how the city interacts with its water cycle. This includes installing inverted wells, which are structures designed to capture rainwater and guide it deep into the ground, and creating more green spaces where the soil can breathe and absorb water. They also call for stricter monitoring, suggesting that water levels should be checked monthly rather than once a year to catch problems early. Furthermore, new housing developments should be required to balance the water they take out with water they put back in. The goal is to create a system where the city does not just consume its water supply but actively participates in replenishing it, ensuring that the taps do not run dry for the generations to come.