Mapping, Monitoring, and Valuing: A Comprehensive Analysis of Ecosystem Services Provided by Dhaka's Green Spaces and Water Bodies
This study analyzes the rapid conversion of Dhaka's green spaces and water bodies into built-up land from 1990 to 2021, revealing a 59.55% decline in ecosystem service value equivalent to an $85 million loss, while highlighting the critical yet spatially unequal and unprotected functions of the remaining natural areas.
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 often thought of as collections of buildings, roads, and people, but they also rely on a hidden, living infrastructure that keeps them habitable. This invisible network consists of green spaces like parks, trees, and gardens, and blue spaces such as rivers, lakes, and wetlands. Together, these natural areas provide essential services that keep a city cool, clean, and safe. They act as natural air conditioners by lowering temperatures, filters that clean the air of harmful particles, and sponges that soak up rainwater to prevent flooding. They also offer places for people to relax and grow food. When a city loses these spaces to concrete and steel, it does not just lose scenery; it loses the very systems that allow it to function, often leading to hotter days, dirtier air, and streets that flood more easily.
A new study focused on Dhaka, the capital of Bangladesh, to understand exactly how much of this natural infrastructure has been lost and what that loss costs the city. Dhaka is a place where the pressure to build is intense, with a population exceeding 22 million people. Researchers set out to map the changes in the city's green and blue spaces over several decades, monitor the condition of what remains, and calculate the monetary value of the services these spaces provide. By combining satellite images from the past with fresh field observations, surveys of residents, and interviews with officials, the team created a complete picture of a city in rapid ecological transition.
The findings reveal a stark and accelerating decline. Between 1990 and 2021, the amount of surface water in the city dropped from nearly 12 percent of the total area to just over 5 percent. This means that in a span of three decades, more than half of the city's visible water disappeared. The loss was even more severe for low-lying lands and water bodies over a longer period, with water bodies shrinking by nearly a third and lowlands by more than half between 1960 and 2008. As these natural features vanished, they were replaced by built-up land, which expanded by nearly 190 percent between 1990 and 2020. This massive shift from nature to concrete has come at a steep price: the total value of the ecosystem services provided by the city's green and blue spaces fell by nearly 60 percent, representing a financial loss of 85 million US dollars.
The study highlights that water bodies were the single most valuable component of this system. When they are lost, the city loses a disproportionate amount of its ability to manage heat, water, and air quality. The remaining green spaces, though small, still work hard. They provide measurable cooling and air purification, and the few remaining wetlands and canals continue to store floodwater and recharge groundwater. However, these benefits are not shared equally. The remaining green cover is so sparse that the average person has access to only a tiny fraction of a square meter of green space, and most of the city's wards have less than 2 percent coverage. This scarcity means that the people living in the most densely built areas are the ones suffering the most from heat and flooding, while the few remaining parks are often overcrowded and difficult to reach.
The research also looked at how people use these spaces and what they are willing to do to keep them. Surveys showed that residents deeply value the ability to cool down, breathe cleaner air, and find a place for recreation. When asked, people indicated they would pay significantly more to visit parks and gardens than the current fees charge, suggesting that the public sees these spaces as far more valuable than they are currently priced. Despite this clear demand and the existence of laws meant to protect wetlands, the study found that enforcement is weak. Officials and planners noted that legal tools exist but are often bypassed by powerful interests, with wetlands filled in for development before monitoring systems can even record the loss.
Ultimately, the study concludes that the city's ecological base has contracted severely and continuously over sixty years. The loss of water and green space has directly contributed to rising temperatures, worsening air pollution, and a decline in groundwater levels. The researchers propose a new way forward that treats the loss of nature as a real economic cost rather than an unavoidable side effect of growth. They recommend a system of regular monitoring that tracks the health of every ward, ensuring that decisions about new construction account for the value of the natural services being destroyed. By making these invisible losses visible and measurable, the study argues that Dhaka can begin to plan for a future where the city's growth does not come at the expense of its ability to survive.
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