The next series of 5 Haby Hints will look at the urban environment and important weather influences. The majority of the Earth’s population now lives in urban areas, thus being aware of urban meteorology is important. An urban area is within the city limits and generally contains business centers, housing, commerce, dense networks of roads and parking. Urbanizing of the planet is one of the primary ways that humans are terraforming the Earth. Terraforming is modifying the surface which is turn changes the temperatures, atmosphere and surface characteristics. This involves removing a large amount of vegetation, altering the land to allow for transportation and commerce and building large numbers of structures, roads and parking lots.

The Earth’s population is currently a little over half urban but as the decades go by it is expected that this fraction will increase. In a few decades up to 75% of the world’s population could be living in urban centers. At the same time the world population continues to grow. This will cause most urban centers to continue to expand into the neighboring countryside. The population of most urban centers will grow and the city limits of urbanization will continue to expand. As urban centers expand over the globe, they will have a more pronounced influence on weather and climate. This writing is particularly interested in the influence on temperature.

Urban centers tend to have an influence of increasing the temperature. This is due to less moisture and less vegetation. Vegetation is an important factor to regulating temperature. Vegetation absorbs some of the sun’s energy to produce photosynthesis. Vegetation contains moisture and moisture is more abundant where there is more vegetation. Water has a high heat capacity and is thus able to absorb an abundance of solar energy. Wet soils and plants do not warm as quickly as materials such as concrete and metal when absorbing solar radiation due to the high heat capacity of water. When rain falls into an urban environment, it quickly runs off into the drainage system instead of soaking into the ground. The expansion of urban centers will contribute to less water and plants, and this has a net heating impact. A term used for this is the urban heat island. Urban construction tends to warm quickly when exposed to sunlight. As urban locations become a greater percentage of the surface land cover on Earth it can be expected that temperatures will continue to warm.