To What Extent Do Urban Areas Modify Their Climates

To what extent do urban areas modify their climates?

Human activity often influences the climate of an area more often than not in urban areas due to a higher population density in these regions. Characteristics such as temperature, pressure, wind, precipitation and cloud cover can be affected yet they often change temporally and spatially due to the varying effects of human activity. Thus meaning the extent to which urban areas modify their climates also differs from place to place. But there is an overall consensus that urban areas modify their climates to a relatively limited extent, the changes they incur on their climate are fairly minor, however at times they are important enough to initiate a response.

Out of all factors, urban areas modify temperature to the greatest extent out of any, often increasing temperatures as much as 5 degrees giving urban zones the name of ‘heat islands’. The increase in temperatures in these regions is largely down to short-wave radiation being absorbed during the day by dark surfaces, such as tarmac, which is present on roads and car parks in particular. Furthermore, the use of cars in cities along with the presence of factories means there is often a great deal of pollution, leading to the formation of a pollution dome, which allows short-wave radiation to enter a cities atmosphere but traps it from leaving thus increasing temperatures in these areas. Considering that major cities across the world have an incredibly high use of cars, with 80% of commuters in Los Angeles using car, this can have a fairly large effect on urban climates. Yet considering that the heat from the short-wave radiation is simply stored during the day it is questionable the extent to which it truly affects the climate as it is released at night, when temperatures are far colder anyway. Another factor increasing the level of heat in urban areas is the lack of vegetation present, with a decreased amount of vegetation; cities lose the shade and cooling effect of trees, the low albedo of their leaves, and the removal of carbon dioxide. The intensity in the central London area rose by around 3 degrees Celsius during an hour-long period, while Richmond Park is about 1 degree Celsius cooler than its surroundings. Considering rural areas contain a far greater amount of vegetation the difference between the temperatures in the two areas is likely to be extended. For example temperature differentiated in the urban area of London and the rural area of Wisley, by around 8-9 degrees Celsius during the summer of 2003 on a number of occasions. Emphasizing the effect urban areas can have on their climate considering the huge difference between temperatures. However considering the fact that all of these factors vary greatly in these areas and that schemes have been created to mitigate the effects of things like pollution such as London’s low emission zone which is the largest out of any in the world, means that at times temperatures are not effected as much in urban areas to a far lesser extent.