But Quattrochi and co-investigator Jeffrey Luvall, also at GHCC, have found some hope in the midst of the sweltering cities. Trees can help reduce temperatures. That's part of what they want to define and study in Atlanta. By contrast, wooded areas, even small trees islands in the parking lot, show as cool spots. The difference has to do with how materials absorb and release heat.
Asphalt absorbs heat from the sun and quickly releases it as heat radiation.
Even grassy areas near the woods appear hotter than the woods because a meadow has less vegetation and shade. It's important to understand that just as much sunlight falls on cities as on woodlands of the same size. The difference is in how urban materials react to the absorption of solar radiation. Asphalt in parking lots and on rooftops, in particular, soaks up everything and reradiates it as thermal infrared radiation. On the other hand, water absorbs a large amount of heat before its temperature rises 1 degree, and takes a long time to release it.