Cities Getting Hotter: The Surprising Truth About Urban Plants

Cities are getting hotter, and plants are supposed to help. But it's not that simple. In some places, plants can make things worse. This is a big deal because more than half the world's people live in cities. And cities are getting hotter because of something called the urban heat island effect. Scientists looked at 761 big cities in 105 countries. They used satellites and weather data. They found something surprising. In dry places, plants can actually make things hotter. This happens in about 22% of cities that don't get much rain. Grass and crops are the main culprits. They don't cool the air like trees do. Why does this happen? In dry places, plants don't have enough water. They can't cool the air by releasing water vapor. Instead, they make things hotter by absorbing heat. This is the opposite of what they're supposed to do.During heatwaves, things get even worse. Trees fail to cool cities in 25% of cases. Grass and crops do even worse. They fail to cool cities in 71% and 82% of cases, respectively. This is because dry air makes it hard for plants to release water vapor. Also, their leaves can't let in enough air to cool things down. So, what's the solution? Scientists say we need to be smart about planting. In dry cities, we might need to use different types of plants. Or we might need to use other methods to cool cities. For example, we could use surfaces that reflect heat. This is called high-albedo surfaces. But we need to be careful. Planting the wrong types of plants in the wrong places can make things worse. We need to think about the climate of each city. And we need to choose plants that will actually help.