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The first thing to be observed is the contrasting levels of heat in relation to urban features. Large concrete buildings and roads due to their thermal capacity store and emmit greater heat than the lighter surfaces and vegetation. From the image within Tokyo it becomes clear that we should also expect a temperature gradient along a rural-urban transect.
This temperature gradient is known as the Urban Heat Island Effect.
The Urban heat island effect is caused by a number of factors but primarily the nature of the building materials.
Building material have vastly different physical properties to soils and plants. Concrete and bitchamin warm up rapidly in the day time in contrast to waterways and parks. Due to the nature of the surface its albedo is lower.
Much more heat is absorbed and conducted through the material. This heat is then slowly released during the night, adding warmth to the urban atmosphere. This keeps urban climates relatively high and the contrast between the urban environment and the rural fringe is greatest at night.
Building materials therefore have heat storage capacities. Another factor that leads to an urban heat island effect relates to the amount of pollutants in the atmosphere. Cities are home to industry and many homes, that remain heated through winter months, people are mobile and vehicle combustion is also a huge factor of consideration.
Research shows that on Manhattan Island, in the average January, the amount of heat produced from combustion alone is greater than the amount of energy from the sun by a factor of 2. In summer this ratio is only 0.
The urban surface energy budget can be seen in the diagram below. The two diagrams above show a rural-urban transect from the rural urban fringe through to the high-rise characteristics of the central business district and back to the rural-urban-fringe.
A number of observations can be made. Firstly, the urban temperatures are at their highest in the mid-afternoon over the the CBD. Also secondary nodes or peaks of high temperature apppear over significantly built-up areas such as that seen over the suburban residential areas.
A second observation tells us that at night temperatures are significantly lower than day time temperature. Although the temperature range from rural to city centre is often greatest at night due to the high heat storage capacity of building materials compared to vegetation.
The graph to the left shows two sections. Section A shows the contrast in cooling between urban and rural areas. Both surfaces begin to cool several hours before sunset but rural areas cool rapidly compared to urban area that retain heat better.
Rural temperature during calm atmospheric conditions are also seen to fall lower than urban temperatures. Section B shows the heat island intensity growing mid-late afternoon and at its highest a few hours after sunset. The isotherm map below shows lines of equal atmospheric temperature for a hypothetical city.
The second diagram shows the differences in evapotranspiration and run-off. This difference contributes to higher surface area temperatures.
Reducing Urban Heat Island Effects. Urban Canopy and Urban Boundaries When discussing the urban heat island effect a number of distinctions should be made.
Firstly there are three types of heat islands: The urban canopy layer UCL is the layer of air closest to the surface in cities, extending upwards to approximately to the mean building height as shown in the diagram.
Above the urban canopy layer lies the urban boundary layer UBL. This may be 1km or more in height during daytime, but as little as a few hundred meters at night.Why cities can be the solution to climate change. City mayors are directly accountable to their constituents for their decisions, and are more nimble than state and national elected officials to take decisive action—often with immediate and impactful results.
What our cities do individually and in unison to address climate change can set the. The application of urban climatic mapping to the urban planning of high-density cities: The case of Kaohsiung, Taiwan as characterized by their compact urban fabric and large urban populations (Kraas, Most German cities have developed their own UCMaps (Ren et al., ).
Sep 27, · Most of the world's major cities today have been important cities for several hundred years, so they became important cities before the development of motorized transport (and later refrigeration) that reduced cities' dependence on their surroundings for food .
Climate on a local scale: urban climates Human activity has a big influence on the climate of an urban area. Climate is the long term behaviour of the atmosphere in a specific area, with characteristics such as temperature, pressure, wind, precipitation, cloud cover and humidity etc.
Cities have emerged as key partners in the fight against climate change, but their impact goes beyond the numbers. It hasn’t happened overnight, but today more and .
Large cities commonly create their own climate and weather this weather that they create is known as the ‘urban climate dome’, within which the weather is different from the surrounding rural areas.