Long-term urban expansion, land-cover transitions and estimated ecosystem service value in Kathmandu Valley, Nepal, 1988–2024
This study analyzes Kathmandu Valley's land-use changes from 1988 to 2024, revealing that rapid urban expansion driven by cropland conversion has reduced total ecosystem service value by 12.18%, thereby highlighting the urgent need for sustainable land-management strategies that prioritize agricultural conservation and green-blue infrastructure.
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In the heart of the Himalayas, the Kathmandu Valley is a bowl-shaped basin where the air is thin and the seasons are sharp. For centuries, this landscape has been a patchwork of rice fields, forests, and small villages, all cradled by steep hills. But like many places around the world, it is changing fast. As cities grow, they do not just expand into empty space; they swallow up the land that feeds people and the green spaces that clean the air and water. Scientists who study these changes look at two main things: how the physical map of the land is being redrawn, and what that redrawing means for the natural services the land provides. These services are the free benefits nature gives us, such as crops for food, forests that store carbon, and rivers that filter water. When a field is paved over for a new neighborhood, those services disappear. The question is not just how much land is lost, but exactly which parts of the landscape are being replaced and how that shift changes the value of the natural world remaining.
A recent study by Amrit Dhakal, a researcher at Prince of Songkla University, takes a long, hard look at this transformation in the Kathmandu Valley over a thirty-six-year period, from 1988 to 2024. Instead of taking new satellite photos, the researcher re-examined a detailed map of the valley that had already been created by other scientists. This existing map broke the valley down into five simple categories: buildings and paved areas, farm fields, green vegetation, bare or rocky ground, and water. By using this consistent map for six different years, the researcher could trace exactly how the land changed from one date to the next, rather than just comparing the start and end points. The goal was to see not only how much the city grew, but to identify the specific path of that growth: was the city eating up forests, or was it taking over the most productive farmland?
The results show a dramatic reshaping of the valley. In 1988, the built-up area, which includes houses, roads, and factories, covered only about 38 square kilometers. By 2024, that number had jumped to nearly 198 square kilometers. This is a massive increase, meaning the city has more than quintupled in size. At the same time, the amount of farmland shrank significantly, dropping from over 418 square kilometers to about 245 square kilometers. The study found that the city did not grow randomly; it grew by directly replacing the fields. In every single time period measured, the most common change was farmland turning into built-up land. Over the entire thirty-six years, about 155 square kilometers of cropland were converted into urban areas. This is a specific and consistent pattern: the city is expanding by paving over the agricultural land that once surrounded it.
While the farmland disappeared, the total amount of green vegetation actually increased slightly, growing by about 11 square kilometers over the same period. However, this small gain in green space did not stop the overall value of the land's natural services from falling. The researchers calculated the estimated economic value of the ecosystem services provided by the land in each year. In 1988, the total value was estimated at about 82.77 million US dollars per year. By 2024, that figure had dropped to 72.69 million dollars, a loss of roughly 12 percent. This decline happened because the land that was lost—farmland—had a high value for producing food, and the land that replaced it—buildings—was assigned a value of zero in this specific calculation. Even though the green vegetation grew a little, it could not make up for the loss of the productive fields.
The study also highlights a crucial detail about how we measure these values. The researchers found that the total number they calculated depends heavily on how much they value the green vegetation. In 1988, the value of the vegetation made up about 60 percent of the total estimated value. By 2024, because the farmland had shrunk so much, the vegetation made up over 72 percent of the total. This does not mean the plants became more valuable or that the forests improved; it simply means that as the farmland disappeared, the remaining green areas became the main source of the value that was left. The researchers are careful to note that their numbers are not a perfect measure of real money lost, but rather a way to compare how the mix of land types has shifted. They also point out that their maps group all types of green plants together, so they cannot tell if the new green areas are healthy forests or just small patches of grass.
The findings suggest that for the Kathmandu Valley to manage its growth sustainably, planners need to look beyond just the total size of the city. They need to pay close attention to the specific fields that are being converted into buildings. The study shows that the pressure on farmland is not just a historical fact but a continuing trend, with the largest amount of farmland lost in the most recent period from 2016 to 2024. The researchers argue that protecting the remaining agricultural land and maintaining connections between the green spaces and water bodies is essential. While the city will continue to grow, understanding exactly which parts of the landscape are being sacrificed allows for better decisions about where to build and what to save, ensuring that the valley does not lose the very resources that support its people.
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