การฟัง TOEFL

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Listen to part of a lecture in an environmental science class. Professor: Today we're going to discuss a surprising factor in urban heat islands—the role of trees. Now, you might think that planting more trees always cools a city, and that's true in most cases. Trees provide shade and release water vapor through transpiration, which lowers air temperature. However, recent studies have shown that in some arid regions, like parts of the southwestern United States, trees can actually increase nighttime temperatures. Why? Because trees trap heat radiating from the ground and buildings, preventing it from escaping into the atmosphere. This is especially true when trees are dense and close to structures. So, while trees are generally beneficial for reducing daytime heat, their effect on nighttime temperatures depends on the climate and the arrangement of vegetation. In dry areas, the cooling from transpiration is minimal, but the heat-trapping effect is significant. This means urban planners need to consider local climate conditions when deciding where and how many trees to plant.