Urban Heat Island Dynamics and 2030 Thermal Scenario in Pokhara, Nepal Using Landsat and CA– Markov Modeling

Cities are not just collections of buildings and roads; they are complex machines that interact with the sun and the air in ways that change the local climate. When natural ground covered with soil and plants is replaced by concrete, asphalt, and rooftops, the surface changes how it absorbs and holds heat. Vegetation cools the air through a process similar to sweating, where water evaporates from leaves, while bare soil and paved surfaces soak up solar energy and release it slowly, often making the area significantly warmer than the surrounding countryside. This phenomenon, known as an urban heat island, is a growing concern for city planners and residents alike, as rising temperatures can strain energy systems, worsen air quality, and threaten human health. Understanding how these thermal patterns evolve requires looking at the city not just as a map of streets, but as a living surface that breathes, heats, and cools in response to the land beneath it.

In the heart of the Himalayas, the city of Pokhara, Nepal, is undergoing a rapid transformation that offers a clear view of this process. A recent study focused on the city's core urban area, a specific zone of about 37 square kilometers where the most intense development is happening. Researchers set out to understand how the shift from farmland to buildings has altered the temperature of the ground over the last decade. They looked at satellite images taken in 2014, 2019, and 2024 to track changes in what covers the land. By using advanced computer tools, they mapped out where crops, forests, water, and settlements were located, and then measured the actual temperature of the ground surface in those same years. They also used a mathematical model to project what the city might look like in 2030, allowing them to see how these changes could affect future heat levels.

The results paint a picture of a city that is getting hotter as it grows. In 2014, the study area was dominated by cultivation, with crops covering nearly 78 percent of the land, while settlements occupied only about 20 percent. By 2024, the balance had shifted dramatically. The area covered by settlements, including roads, buildings, and airport infrastructure, had grown to nearly 38 percent, while the land used for farming had shrunk to about 56 percent. This loss of green, cultivated space was replaced by impervious surfaces that do not cool the air. As the land cover changed, the temperature of the ground rose sharply. The average temperature of the surface in the study area increased from just under 30 degrees Celsius in 2014 to nearly 37.5 degrees Celsius in 2024. The hottest spots, which reached temperatures above 36 degrees in 2014, were soaring to over 44 degrees by 2024.

The study confirmed that the type of land cover is the primary driver of these temperature differences. Areas covered by forests and dense vegetation remained the coolest, while barren land, exposed soil, and construction sites became the hottest. Settlements, with their mix of buildings and roads, also recorded very high temperatures, often rivaling the bare earth. The researchers found that as the city expanded, the patches of green vegetation became more fragmented, breaking up the continuous cooling effect that large fields and forests provide. This fragmentation meant that the cooling influence of plants was reduced, allowing heat to build up more easily in the newly developed areas. The data showed a clear link: where the vegetation index dropped, the ground temperature rose.

To ensure their measurements were accurate, the researchers compared their satellite data with other sources. They checked their ground temperature readings against data from a different satellite system that provides broader, lower-resolution views, finding a strong agreement between the two. They also looked at air temperature records from a local weather station to see if the trends matched. While the ground temperature measured by the satellites was naturally higher than the air temperature measured two meters above the ground, the trends were consistent, showing that the surface was indeed warming in step with the city's growth. This cross-check gave the researchers confidence that their maps of heat were reliable.

Looking ahead, the researchers used a computer model to simulate the city's future based on the trends observed over the last decade. The model suggests that if current patterns continue, the settlement area will expand to cover more than half of the core urban zone by 2030, leaving less than half for cultivation. This projection indicates that the areas experiencing the most intense heat will also grow. The model predicts that by 2030, more than half of the study area could fall into the categories of high or extremely high heat intensity. These hot zones are expected to concentrate around the dense urban core, the airport, and major transportation corridors, creating a landscape where heat is the dominant feature.

The findings serve as a warning and a guide for the future. The study highlights that the rapid conversion of farmland and open spaces into built-up areas is directly responsible for the intensifying heat in Pokhara. It suggests that without intervention, the city will continue to warm, with the hottest zones expanding to cover a majority of the urban core. The researchers emphasize that protecting the remaining green spaces, managing exposed surfaces, and integrating cooling strategies into urban planning are essential steps to mitigate this trend. By using satellite data to monitor these changes, city planners can identify the areas most at risk and prioritize efforts to bring vegetation back into the urban fabric, ensuring that the city remains livable as it continues to grow.