DISCUSSION: Have you ever taken a vacation to a city and then drove by a rural area for a pit stop? Have you stopped and thought, “man it sure is cooler here than in the city?”
There’s a name for this feeling. It’s called the Urban Heat Island. In simpler terms, it says that cities are 1-5°C warmer than rural areas. The effects of this phenomenon can go beyond city limits. These are the reasons for the Urban Heat Island: reduction in evapotranspiration, composition of materials in the city, pollution, and excess heat from human (anthropogenic) activity.
By definition, evapotranspiration is when water gets transferred to the atmosphere by evaporation from the land and transpiration from plants. Unless there is a garden or park within city limits, there is reduced vegetation in the city. Therefore, this allows for more sensible heat and warmer temperatures. In addition to this, areas where water can’t be absorbed within the city promote runoff.
Urban areas have lower albedos, which means less reflection and more absorption of sunlight. The construction materials have high heat capacities and thermal conductivity. These are defined, respectfully as, the ability to raise a degree of an object by 1 degree Celsius, and the ability to conduct heat. Energy is stored in the day and released at night.
Pollution can act like a shield over the city. What is meant by this “shield of pollution” is that this “shield” can act as a barrier against outgoing longwave radiation from leaving. Once this radiation attempts to leave, the “shield” will just send it right back to the city. This explains the increase in nocturnal temperature in cities.
The following things humans do can release heat: transportation, cooling apparatuses such as air conditioners, street lights, etc.
In conclusion, the effects of urbanization can have an immediate effect on the weather.
To learn more about Urban Weather, click here!
“©2017 Weather Forecaster Jennifer Naillon