Heat Island Definition

An urban heat island means that an urban area or metropolitan area is much warmer than surrounding rural areas due to human activities. In recent years, a number of adaptation measures have been developed to mitigate the damage caused by the urban heat island phenomenon. This book «Adaptation Measures for Urban Heat Islands» helps the reader understand the relative performance of these adaptation measures, methods and analyses in relation to their creation and maintenance, evaluation methods and the role of policy and governance in their implementation. A number of case studies stretch far into the urban heat island literature. This book organizes the three activities the authors worked on in the Osaka Heat Island Countermeasure Technology Consortium; Organization of adaptation measures, study of the specific image of the adaptive city and study of the evaluation method of the adaptive city. Research has been conducted in some areas, suggesting that metropolitan areas are less susceptible to weak tornadoes due to the turbulent mix caused by the heat of the urban heat island. [49] Using satellite imagery, the researchers found that urban climate has a noticeable impact on plant growing seasons, which are up to 10 kilometers (6.2 miles) from the outskirts of a city. Growing seasons in 70 cities in eastern North America were about 15 days longer in urban areas than in rural areas outside the influence of a city. [50] Urban building materials are another reason why urban areas retain heat. Many modern building materials are impermeable surfaces. This means that water cannot flow through surfaces such as a brick or piece of cement as it would through a plant. Without a cycle of water flow and evaporation, these surfaces have nothing to cool them.

Monthly rainfall is heavier downwind in cities, partly because of the ICU. Increased heat in urban centres increases the length of growing seasons and reduces the appearance of weak tornadoes. UHI reduces air quality by increasing the production of pollutants such as ozone, and reduces water quality as warmer water flows into the region`s waterways, putting pressure on its ecosystems. First of all, materials such as asphalt, steel and brick are often very dark colors – such as black, brown and gray. A dark object absorbs all wavelengths of light energy and converts it into heat so that the object becomes hot. In contrast, a white object reflects all wavelengths of light. The light is not converted into heat and the temperature of the white object does not increase significantly. For example, dark objects – such as building materials – absorb heat from the sun. The use of lightweight concrete has proven effective in reflecting up to 50% more light than asphalt and lowering the ambient temperature. [86] A low albedo characteristic of black asphalt absorbs a significant percentage of the sun`s heat, resulting in warmer temperatures near the surface.

By asphalting with lightweight concrete, in addition to replacing asphalt with lightweight concrete, communities may be able to lower average temperatures. [87] However, research on the interaction between reflective walkways and buildings has revealed that solar radiation reflected from light sidewalks can increase the temperature of buildings if neighbouring buildings are not equipped with reflective glass, increasing the need for air conditioning. [88] [89] The urban heat island effect is a significant environmental problem faced by all major urban centres. Local increases in average annual temperature are well documented, as are the costs and environmental impacts associated with increased cooling. There are a number of mitigation measures, which usually involve an increase in surface reflection or albedo and an increase in urban vegetation. The measures described in this chapter are not exhaustive but generally representative of available solutions. Any effective solution will certainly include a combination of measures, including cool sidewalks, cool roofs, an increase in urban forests and green roofs. Figure 1. Schematic representation of an urban heat island: vertical view (top) (cross-section); (bottom) Top view of the corresponding projection. The thick dotted lines show the intensity of the UHI air temperature, which is read from the scale (°C) on the left in the vertical view. The thick arrows show a UHI convection cell advocated by the windwind downwind of the city center.

The boundaries of an urban heat plume (also enlarged in the wind direction) are shown. Other aspects presented are the limits of the surface temperature UHI, the UHI of the canopy and boundary layer, convective clouds, incoming and outgoing radiation beams (A and B) and the urban canyon. One researcher found that high UHI intensity correlates with increased concentrations of air pollutants that accumulate at night, which can affect the next day`s air quality. [66] These pollutants include volatile organic compounds, carbon monoxide, nitrogen oxides and particulate matter. [64] The production of these pollutants combined with higher temperatures in ICUs can accelerate ozone production. [66] Surface ozone is considered a harmful pollutant. [66] Studies suggest that high temperatures at ICU may increase on polluted days, but also indicate that other factors (e.g., atmospheric pressure, cloud cover, wind speed) can also affect pollution. [66] Studies in Hong Kong found that areas of the city with lower urban outdoor air ventilation tended to have stronger urban heat island effects[67] and significantly higher overall mortality[68] than better-ventilated areas. Other causes of ICU are due to geometric effects.

Large buildings in many urban areas offer multiple surfaces to reflect and absorb sunlight, increasing the efficiency with which urban areas are heated. This is called the «urban canyon effect». Another effect of buildings is wind blockage, which also inhibits convection cooling and prevents pollutants from dissipating. depression, dementia, Parkinson`s disease) are more at risk at high temperatures and «need to be very careful»[63], as cognitive performance has been shown to be affected differently by heat[65]. People with diabetes,[63] are overweight,[64] sleep deprived,[64] or have cardiovascular/cerebrovascular disease, should avoid too much exposure to heat. [63] [64] Some common medications that affect thermoregulation may also increase the risk of mortality. Examples include anticholinergics[63], diuretics[63], phenothiazines[64] and barbiturates. [64] Not only health, but also heat can influence behaviour. A U.S. study suggests that heat can make people more irritable and aggressive, and notes that violent crime increased by 4.58 per 100,000 per degree of temperature increase. [66] Caption: These NASA/USGS Landsat satellite images show the cooling effect of plants on the heat of New York. On the left, the dark green areas of the map have dense vegetation.

Notice how these regions correspond to the dark purple regions – the ones with the coolest temperatures – on the right. Photo credit: Maps by Robert Simmon, with data from the Landsat program. There is a myth that urban heat is responsible for climate change. This is not the case. Urban and rural environments around the world are warming because there are more greenhouse gases in the atmosphere. In fact, some of the regions of the world that have warmed the most are in the Arctic, far from the cities. In order to cool urban heat islands, some cities «illuminate» roads. This is done by covering black asphalt roads, parking lots, and dark roofs with a more reflective gray coating. These changes can significantly reduce urban air temperature, especially during the heat of summer. The development and implementation of comprehensive mitigation strategies for urban areas will take a long time. If we start the process, we will eventually reach the desired destinations – a 1000-mile journey starts with what`s under our feet.

Given that huge investments have been made in infrastructure and buildings without considering the consequences in terms of urban heat islands, the final solution requires both a change in current construction techniques and a serious consideration of renovation options, if any. Despite the long-term benefits of driveways and cool roofs, the initial cost of capital is often higher than traditional construction approaches, and certain incentives or regulatory changes will be required to encourage the implementation of these mitigation strategies.