Tuesday, July 23, 2019

Urban Areas Modify Climates Essay Example for Free

Urban Areas Modify Climates Essay Urban areas climate is often significantly different to the surrounding rural areas, this is why urban areas are often described as having their own â€Å"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 dev elop 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 activity within a city. The reason behind this is the fact that cities have a higher average number of particles within the air (due to industrial activity releasing pollution) these particles act as a condensation nuclei and encourage fog formation (usually under high pressure conditions) when pollutants become trapped within the lower atmo sphere water vapour can condense around these particles and cause smog to form. These were common in 20th century London. Smog can have devastating effects and can cause serious respiration problems for people and trigger diseases such as emphysema, more recently photochemical smog has been developing this is due to polluting gases such as nitrous oxides and carbon monoxide react with sunlight to produce a cocktail of harmful gases which can cause devastating health effects. Air quality within urban areas is also dramatically different than surrounding areas. Within cities there is a significant amount of pollution, there are different types of pollution and they have different effects. Suspended particulate matter is solid matter within the urban atmosphere such particles are usually less than 25micrometers in size and cause problems such as fog/smog, respiratory diseases, soiling of buildings. Sulphur dioxide is usually released from combustion of fossil fuels causes a hazard known as acid rain (due to its acidic nature) and this can corrode away at buildings it also contributes to respiratory disease s Carbon monoxide is also released from incomplete combustion of fossil fuels and is a poisonous gas that prohibits haemoglobin within the blood to uptake oxygen, therefore it is potentially life threatening. Consequently due to all the pollutants the number of â€Å"blue sky days† were the sky is visibly blue can be significantly reduced consequently reducing the amount of sunlight upon the city, there have been policies introduced in cities worldwide to reduce pollution levels and increase the number of blue sky days. The serious effects of poor air quality can be perfectly illustrated with Beijing were the public wear masks to protect themselves from the poor air and serious efforts have been made to cut down on polluting sources. The urban layout of buildings of various different sizes vastly affects the wind pattern in the upper atmosphere; there are effects on wind speed, direction and frequency. The surface area of cities which is very uneven exerts a powerful frictional drag on the air moving over and around this creates strong turbulence giving rapid and abrupt changes in both wind direction and speed, consequently average wind speeds are lower within the city. High rise building significantly disturb airflows over urban areas, they deflect and slow down the upper atmosphere winds, and this can creature strong vortices and eddies. These fast turbulent winds can become funnelled in-between buildings producing a venturi effect this can swirl up litter and make walking down pavements difficult In conclusion urban areas can significantly influence their climate and cause it to be very different compared to surrounding rural areas, urban areas cause numerous amounts of changes in the climate surrounding them and cause higher temperatures, higher precipitation rates, effect the air quality and completely disturb the upper atmosphere wind pattern.

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