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Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about urban heat islands. As you know, cities tend to be warmer than surrounding rural areas. This is due to several factors. First, concrete and asphalt absorb and retain heat during the day and release it slowly at night. Second, buildings block wind, reducing natural cooling. Third, human activities like driving and air conditioning generate waste heat. However, there are mitigation strategies. One effective method is increasing green spaces, such as parks and green roofs. Plants provide shade and release moisture through transpiration, which cools the air. Another strategy is using reflective materials for roofs and pavements. These materials, often called 'cool roofs' or 'cool pavements,' reflect more sunlight and absorb less heat. A study in Los Angeles found that increasing the albedo of roofs and roads could reduce the city's temperature by up to 3 degrees Celsius. While green spaces are more aesthetically pleasing, cool surfaces are often cheaper and easier to implement. So, which approach is better? Well, it depends on the local climate and budget. In dry regions, water for plants might be scarce, making cool surfaces more practical. In wetter climates, green roofs can also help manage stormwater runoff. So, a combination of both is often the best solution.