Geospatial Assessment of Urban Growth Patterns and Its Impact on Land Surface Temperature
This study utilizes remote sensing, GIS, and machine learning to demonstrate that rapid urban expansion in Dera Ghazi Khan, Pakistan, from 2000 to 2025 has significantly intensified the Surface Urban Heat Island effect by increasing Land Surface Temperature through the conversion of vegetation and barren land into built-up areas, while precipitation variability modulates these thermal impacts.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Cities are not just collections of buildings; they are living systems that change the air we breathe and the heat we feel. When natural ground covered with soil and plants is replaced by concrete, asphalt, and rooftops, the way the earth absorbs and releases energy shifts dramatically. This transformation creates a phenomenon known as the Surface Urban Heat Island, where a city becomes significantly warmer than the surrounding countryside. This happens because man-made materials soak up sunlight and hold onto heat, while natural landscapes cool themselves through the evaporation of water from plants and soil. As the world's population moves into cities, understanding how this growth alters local temperatures is no longer just an academic exercise; it is a matter of public health and survival, especially in regions that are already hot and dry.
In the arid landscape of Pakistan, a team of researchers set out to map exactly how a growing city changes its own climate over a quarter of a century. They focused on Dera Ghazi Khan, a major secondary city in the Punjab province, situated between the Indus River and the Sulaiman Mountains. This location is critical because it is already prone to extreme heat, and the city has been expanding rapidly without a strict plan. The researchers wanted to see how the conversion of farmland and open desert into residential and commercial zones affected the ground temperature and whether rainfall patterns could soften or worsen these effects. To do this, they did not rely on a few weather stations scattered across the city. Instead, they looked at the entire region from space, using a series of satellite images taken every five years from 2000 to 2025.
The team used powerful cloud-based computing to process thousands of images from satellites, allowing them to classify the land into four distinct types: water bodies, built-up areas, agricultural fields, and barren land. By tracking these categories over twenty-five years, they could see the city's footprint expanding in real time. The data revealed a stark transformation. In the year 2000, the built-up area covered about 354 square kilometers. By 2025, that number had swelled to nearly 570 square kilometers. As the city grew outward, it consumed vast amounts of barren land, which shrank from 778 square kilometers to just 213 square kilometers. While agricultural land fluctuated, the overall trend was clear: the natural, porous ground was being replaced by hard, impervious surfaces that trap heat.
This physical change had a direct and measurable impact on the temperature of the ground. The researchers calculated the Land Surface Temperature, which is the actual temperature of the ground as seen from above, rather than the air temperature measured by a thermometer. They found that the hottest spots on the map were always the same places: the dense urban core and the newly developed edges where concrete and asphalt had replaced the earth. In 2015, a particularly hot year, the average Land Surface Temperature reached around 49 degrees Celsius, a variation attributed to precipitation patterns where years with higher rainfall also supported better vegetation and less thermal stress. The analysis showed that the more the city built up its infrastructure, the hotter the ground became. Conversely, areas with water, such as the Indus River and irrigation canals, and areas with dense vegetation remained significantly cooler. These natural features acted as thermal buffers, keeping the ground temperature down through the natural process of evaporation.
The study also looked at how rainfall influenced this heating. The researchers found that years with higher precipitation brought cooler temperatures and healthier vegetation, which helped to mitigate the heat. However, during drier years, the heat accumulated more intensely, especially on the newly constructed surfaces. This interaction suggests that the city's growing heat problem is not just about the buildings themselves, but also about how the local climate responds to the loss of natural cooling surfaces. The researchers identified specific "hotspots" where the heat was most intense, and they watched these areas grow and spread from the city center toward the outskirts over the twenty-five-year period.
To understand the strength of these connections, the team ran statistical tests to see if the increase in built-up land was truly linked to the rise in temperature. The results confirmed a strong relationship: as the amount of concrete and buildings increased, so did the surface temperature. While the statistical models showed that the built-up area was a primary driver of the heat, the study also highlighted the critical role of green spaces and water. The presence of vegetation and water bodies consistently lowered the temperature, proving that preserving these natural elements is essential for keeping the city habitable.
The findings offer a clear warning and a path forward for cities like Dera Ghazi Khan. The rapid, unplanned expansion of the city has intensified the heat island effect, creating a thermal environment that is increasingly dangerous for its residents. The study suggests that simply building more is not a sustainable solution. Instead, the researchers recommend strategic interventions, such as protecting the remaining agricultural buffer zones, restoring water bodies, and incorporating green spaces into new developments. They also suggest using materials that reflect sunlight rather than absorbing it, and designing buildings that allow for better air flow. By using the same geospatial tools that mapped the problem, city planners can now identify exactly where to place trees, parks, and water features to cool the most vulnerable neighborhoods. This research provides a blueprint for how secondary cities in hot, dry regions can grow without baking themselves, turning the data into a guide for a cooler, more resilient future.
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