Urban green space research, knowledge gaps and opportunities for advancing nature-based solutions: Lessons from Bangladesh

Cities are growing faster than ever before, swallowing up the land around them to make room for homes, roads, and factories. As these concrete jungles expand, they often push out the natural world: the trees, the grass, the wetlands, and the open spaces that once cooled the air and absorbed rain. This loss creates a specific problem known as the urban heat island effect, where a city becomes significantly hotter than the surrounding countryside because concrete and asphalt trap heat while the lack of vegetation prevents cooling. To fight this, scientists and planners are increasingly looking toward nature-based solutions. These are strategies that use living systems—like planting trees, restoring wetlands, or creating green roofs—to solve environmental problems, rather than relying solely on machines or concrete structures. The idea is that by weaving nature back into the city, we can lower temperatures, manage floodwaters, and improve the quality of life for everyone living there. However, while this approach is well understood in wealthy nations, there is a significant gap in knowledge about how it works in rapidly developing countries, where the pressure to build is immense and the resources to manage nature are often scarce.

A team of researchers from Charles Darwin University and the United Nations Development Programme decided to fill this gap by looking closely at Bangladesh, one of the most densely populated and quickly urbanizing nations on Earth. They wanted to understand exactly how the country's green spaces are changing, what is driving those changes, and whether current efforts are enough to protect the environment and the people who live there. To do this, they did not go out to measure trees in person; instead, they gathered and analyzed dozens of existing scientific studies and reports about urban green spaces in Bangladesh. They focused on the major cities, including Dhaka, Chittagong, and Khulna, to see the big picture of what has been happening over the last few decades.

The picture that emerged from their analysis is stark. The researchers found that as the cities of Bangladesh have grown, their green spaces have shrunk dramatically. In the northern part of Dhaka, for instance, the amount of vegetation covering the land dropped by as much as 66 percent between 1990 and 2022, while the built-up urban area expanded by 95 percent. In Chittagong, the city's built-up area grew by 18 percent in a single year, replacing fields and wetlands with buildings. This trend is not just about losing a few parks; it is a fundamental shift where natural landscapes are being paved over to accommodate a booming population and new industries. The drivers are clear: people need housing, businesses need space, and the government is building roads and infrastructure. Unfortunately, this expansion often happens without a plan that protects the remaining green areas, leading to a situation where only about 16 percent of Dhaka's total area is covered by vegetation, far below the 17 percent needed for a sustainable city.

The consequences of this loss are already being felt in the physical environment and the daily lives of residents. The researchers found that as the green cover disappears, the temperature of the city's surface rises. In Dhaka, the heat island effect has intensified, with daytime temperatures climbing significantly. In Khulna, the average surface temperature jumped by two degrees Celsius over twenty years, and by 2020, more than half of the city was experiencing temperatures above 33 degrees Celsius, a condition that did not exist in the year 2000. This heat is not distributed equally. The study highlighted that the poorest neighborhoods, often informal settlements with the least amount of trees and open space, suffer the most. These areas, which are frequently located in low-lying zones or on unstable hillsides, face a double threat: they are the hottest places in the city, and they are the most vulnerable to flooding and landslides. The lack of green space means these communities miss out on the cooling shade, the clean air, and the mental relief that nature provides, deepening the inequality between the rich and the poor.

Despite these clear dangers, the researchers found that the solutions currently being discussed in Bangladesh are often too small or too symbolic to make a real difference. While some studies mention rooftop gardens or vertical green walls as helpful ideas, these practices are not yet widespread or supported by strong rules. The existing literature suggests that planting a garden on a roof can lower the temperature of a building and save energy, but these efforts remain isolated experiments rather than a city-wide strategy. The authors argue that the current approach is missing the bigger picture. There is a lack of detailed knowledge about how urbanization is changing the landscape in smaller towns and the areas just outside the big cities. Furthermore, there is no clear, unified policy that tells city planners how to balance the need for new buildings with the need to keep nature alive. The science exists to show that green spaces work, but that knowledge is not being used to guide decisions in the way it should.

To move forward, the researchers propose five key changes that could help Bangladesh and other developing nations turn the tide. First, cities need to integrate green space planning right at the beginning of any development project, rather than trying to add it later. This means creating strict rules that protect wetlands and forests from being paved over. Second, the government needs to create policies that encourage people to keep nature on their land, perhaps by offering tax breaks to those who plant trees or maintain green roofs. Third, different groups that usually work separately—such as the forestry department, city planners, and environmental agencies—must work together to create a unified plan. Fourth, the needs of the poorest residents must be placed at the center of these plans, ensuring that green spaces are built where they are needed most to cool the hottest neighborhoods. Finally, decisions must be based on solid data, using satellite images and scientific monitoring to track changes in temperature and vegetation, so that leaders can see the problem clearly and act before it is too late. The study concludes that while the challenge is immense, the path forward is clear: if cities are to survive and thrive, they must learn to grow with nature, not just over it.