To What Extent Do Urban Areas Modify Their Climate

To what extent do urban areas modify their climate?

Urban areas climate is often significantly different to the surrounding rural areas, this is why urban areas are often described as having their own “micro climate” the differences in urban climates are due to number of different factors.

Urban areas often experience a phenomenon known as a heat island, this is a zone of hot air around and above an urban area which has higher temperatures than the surrounding rural areas consequently cities tend to be warmer than rural areas and the temperature becomes lower progressively as you move towards the rural area with the highest temperatures being in the city centre. Heat islands form due to a variety of factors which are present within cities and not commonly found in rural areas, firstly building material such as concrete and tarmac absorb large quantities of heat during the day (due to their black colour) and when temperatures are cooler (nigh time) the heat is released gradually warming up the surrounding area, this is why the effects of the heat island are more visible at night time because the city remains warm whilst the rural areas are much cooler. There are a large amount of buildings with glass windows within the urban areas, these have a high reflective capacity and reflect heat towards the streets were it is absorbed. Another factor influencing towards to the heat island formation is the heat energy being emitted from industry due to the combustion of fossil fuel which releases heat, domestic heating also contributes towards this, this heat energy warms up the air within the urban area contributing to the dome of warm air which is the heat island. The emission of hygroscopic pollutants from cars also acts as a condensation nuclei leading to the formation of cloud and smog which traps radiation within the area.

Precipitation rates are also significantly different within rural areas, research shows that rainfall is generally higher within the city than surrounding rural areas, a reason for this could is due to the fact the heat island ultimately means temperatures are higher therefore lower pressures will be encouraged to develop above the city, also it means Evapotranspiration rates will be higher within the city causing more cloud formation. Convection rainfall is much higher within the city and this is because the heat island enhances convectional uplift, the city also produces large amounts of water vapour from industrial sources this also means that humidity levels within cities are usually higher

The occurrence of Fog is dramatically higher within urban areas, the great increase in the amount of fog within cities is in accordance with the industrialisation of the city, e.g. In London 1700 there was 29 days of fog but by the 1800 (industrial revolution had occurred) there was over 50 days of fog, this statistic shows that the amount of fog is influenced by the amount of industrial