Technology

Albedo is generally defined as the ratio of diffusely reflected to incident electromagnetic radiation and another term for reflectivity. It is unitless measure of an objects or surfaces reflectivity. The surface of the Earth has an average albedo of 0.3. Given that everything else being equal, a place with higher albedo would tend to be cooler than a place with lower albedo.

Rural areas, where the surface is covered by trees and other vegetations, generally have higher albedo than urban areas. Consequently, the temperature of the rural areas is expected to be lower than the temperature of the urban areas, assuming that any else being equal. The phrase anything else being equal is very important in comparing these two surfaces and any other surfaces. This is due to the fact that albedo is not the only parameter that contributes to temperature of a surface. The emittance of the surface is another factor. An object will radiate more energy than another object of the same surface area if its emittance is larger. Losing more energy would lower its temperature faster, a phenomenon that reduces warming.

Another factor would be the amount of heat from the energy budget goes to latent heat flux. Latent heat flux is the heat used to evaporate water. The heat used in this heat flux does not contribute to the heating of the air. This means that if the latent heat flux is increased, the energy that would be spending to heating would be lessened. This is another reason that the rural is cooler than the urban. Rural areas covered by trees or any other vegetations are kept cool by evapotranspirating the water that these plants absorb. These plants act as an evaporative cooler. Considering that 98 or more of the water absorbed by plants are evapotranspirated, the effect would be an appreciable decrease in temperature.