Urban Heat Island expansion in Khulna City of Bangladesh (1995-2025): Linking LULC change and Land Surface Temperature to heat-related health and economic risks
This study analyzes the spatiotemporal expansion of the Urban Heat Island in Khulna City, Bangladesh (1995–2025), revealing that rapid urbanization and vegetation loss have significantly increased land surface temperatures, thereby exacerbating heat-related health risks for vulnerable populations and causing substantial socio-economic disruptions.
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
Imagine the Earth as a giant, breathing blanket. Sometimes, that blanket gets too hot, not because the sun is shining harder, but because the ground underneath has changed its outfit. This is the world of Urban Heat Islands (UHI). Think of a city like a crowded room where everyone is wearing heavy winter coats made of concrete and asphalt. These materials are like sponges for sunlight; they soak up the sun's energy during the day and hold onto it, releasing it slowly at night. Meanwhile, the countryside is like a room full of open windows and green plants, which act like natural air conditioners, cooling things down through shade and evaporation. When a city grows too fast, replacing its "green windows" with "concrete coats," the whole neighborhood gets stuck in a personal heatwave. This isn't just about feeling sweaty; it's a serious puzzle for scientists trying to figure out how our changing cities are making life harder for the people living inside them, especially when the weather gets extreme.
Now, let's zoom in on a specific neighborhood in Bangladesh called Khulna City. A team of researchers decided to play detective, looking at how this city changed its "outfit" over thirty years, from 1995 to 2025. They used a special kind of telescope from space (satellites) to take pictures of the city's skin, measuring how hot the ground was and what the land looked like. They wanted to see if the city was getting hotter because it was losing its green spaces and gaining more buildings, and how that heat was hurting the people and the economy.
Here is what the detectives found. In 1995, Khulna was mostly green, with about 72.21% of the land covered in vegetation (plants and trees). Fast forward to 2025, and the city had swapped most of its green coat for a concrete one. The green cover shrank to just 45.09%, while the built-up areas (houses, roads, and factories) exploded from 10.12% to 32.16%. It's like watching a forest slowly turn into a parking lot.
As the green disappeared, the heat arrived. The researchers measured the Land Surface Temperature (LST), which is how hot the ground feels. In 2015, 44% of the city had temperatures over 40°C (that's a scorching 104°F). By 2025, that number jumped to 67%. The city was literally baking. They found a super-strong link between the amount of buildings and the heat: the more concrete, the hotter it got. In fact, the connection between the heat and the "Urban Heat Island" effect was almost perfect, with a correlation score of about 0.99. It's as if the buildings and the heat were holding hands tightly.
But the story doesn't stop at hot pavement; it gets personal. The researchers talked to 400 people in Khulna to ask, "How does this heat affect your life?" The answers were eye-opening. The most common complaints were sleep disruption (36.7%) and general heat-related discomfort (35.6%). Imagine trying to sleep when your blanket is on fire; that's what the heat was doing to people's rest.
The heat wasn't hitting everyone equally. The researchers identified the most vulnerable groups, like a "heat risk list." Pregnant women were at the top, with 55.2% reporting severe impacts, followed by elderly people (31.6%) and outdoor workers (27.5%). For pregnant women, the heat wasn't just uncomfortable; it was dangerous, linked to complications like preterm labor. For outdoor workers, the heat meant they couldn't work as hard, leading to lost wages.
The economic ripple effects were just as real. The heatwave acted like a thief, stealing productivity and resources. 40% of people reported water shortages, and 23.8% saw their food prices go up. The heat was so intense that it even caused power outages because the electricity grid couldn't handle the demand for fans and air conditioners. It was a domino effect: hot ground leads to hot air, which leads to broken ACs, which leads to hotter homes and empty wallets.
To make sense of all these tangled clues, the scientists used a math tool called Principal Component Analysis (PCA). Think of this as a way to sort a messy pile of toys into neat boxes. They wanted to know which factors were the "bosses" of the heat. The math showed that Land Surface Temperature (LST), the amount of built-up land (NDBI), and the changes in land use (LULC) were the main drivers. Vegetation (green plants) was the hero trying to cool things down, but it was losing the battle against the expanding concrete.
In the end, this paper tells a clear story: Khulna City is growing fast, but it's trading its cool, green skin for a hot, concrete one. This swap is making the city significantly hotter, which is disrupting sleep, hurting the most vulnerable people, and straining the local economy. The researchers suggest that if the city wants to survive and thrive, it needs to stop the concrete from taking over and start planting more green "air conditioners." They aren't saying this is a solved problem, but they have provided the map showing exactly where the heat is coming from and who is feeling it the most. The next step is for city planners to use this map to build a cooler, safer future.
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