Today, in our environmental science lecture, we'll discuss urban heat islands. As cities grow, concrete and asphalt absorb and re-emit heat more than natural landscapes. This effect can raise city temperatures by up to 5 degrees Celsius compared to surrounding rural areas. One surprising finding is that trees and green roofs can significantly reduce this effect, but their impact varies by climate. In dry regions, for example, trees may compete for water, while in humid areas, they provide more cooling through evaporation. So, when planning green infrastructure, local climate must be a key consideration.