urban heat islands Flashcards
What are the three main factors that contribute to the formation of urban heat islands?
Decreased albedo, reduced atmospheric circulation, and the waste heat from urban processes.
How does decreased albedo in urban areas affect the energy budget and temperature of these areas compared to rural areas?
The relative dark surfaces of an urban landscape absorb and store significantly more solar radiation than surrounding rural areas, which causes urban concentrations of roads and buildings to heat more than suburban and rural areas during the day.
This cause a change in the energy budget of the urban area, often leading to higher temperatures than surrounding rural areas.
Why is the lack of evapotranspiration in urban areas a significant contributor to the urban heat island effect?
Lack of evapotranspiration due to the lack of vegetation in urban areas. With a decreased amount of vegetation, cities also lose the shade and cooling effect of trees, as well as the removal of CO2.
How do tall buildings in urban areas contribute to increased urban temperatures?
The tall buildings provide multiple surfaces for the reflection and absorption of sunlight, increasing the efficiency with which urban areas are heated.
In what way does the blocking of wind by buildings in urban areas affect cooling and pollution?
Another effect of buildings is the blocking of wind, which also slows cooling by convection and prevents pollution from dissipating.
How does waste heat from various sources contribute to the urban heat island effect?
Waste heat from automobiles, air conditioning, industry, and other sources also contributes to increased urban temperatures.
How can high levels of pollution in urban areas exacerbate the urban heat island effect?
High levels of pollution in urban areas can also increase the urban heat island effect, as many forms of pollution change the radiative properties of the atmosphere.
What is the typical temperature difference between the centre of a city and its surrounding rural areas at night?
Many cities that exhibit a heat island effect have the largest temperature differences at night. The typical temperature differences is several degrees between the centre of the city and surrounding areas of rural and natural vegetation.
The difference in temperature between an inner city and its outer suburbs can be seen in daily weather reports. The annual mean air temperature of a city with one million people or more can be 1 degrees to 3 degrees warmer than its surroundings. In the evening, the difference can be as high as 12 degrees
How does the urban heat island effect relate to the increasing rates of urbanization and growth of megacities worldwide?
With increasing rates of urbanisation throughout the world, and the rapid growth of megacities, the urban heat island effect has the potential to impact on significant proportions of the earths population.
Explain the bi-directional relationship between climate change and land cover change due to the urban heat island effect and provide an example of its impact on forests.
The changes in climate as a result of the urban heat island effect exhibit a bi-directional relationship with land cover change, creating another positive feedback loop. As temperature increases and rainfall declines (due to decreased albedo and evapotranspiration with deforestation and the growth of urban settlements), trees become stressed and therefore are more vulnerable to pest attacks.
For example, the bark beetle which has ravaged European conifer forests, and diseases such as Dieback disease which is prevalent in the jarrah forests of southwest western Australia. This subsequently leads to a decline in forest cover, demonstrating how changes in climate, caused by a land cover changes, can affect land cover change in return.
