Uploaded on 2016-03-01 by EttoreMurabito

The temperature differences between urban areas and their surrounding are shown below for five American cities. These cities have been chosen as representative of different areas and climates in the United States. The three numbers provided for each cities represent the following quantities: - Highest difference between city and nerby rural area. - Average difference in summer temperature between city and nearby rural area. - More days above 90° F each year, than rural areas (Note: Temperatures are provided in Fahrenheit) 1. Tampa - 12° F | 1.4° F | 11 days 2. Tucson - 16° F | 0.42° F | 12 days 3. Los Angeles - 27° F | 2.4° F | 5 days 4. Boston - 15° F | 1.3° F | 5 days 5. Chicago - 21° F | 2.2° F | 8 days **2. Which are the main UHI effects that you can identify in your area?** The two image below shows the Google Earth map of Manchester Urban Heat Island on the 6th of March 2009 between 6 and 8am UTC. In Fig.1 one can see the apparent difference in temperature between the wide Greater Manchester urban area and its more rural surrounding. Fig.2 shows differences *within* the urban area of Greater Manchester. One can see clear ‘hot spots’ in central Manchester and central Stockport. Even more interestingly, there is a clear relationship between temperature and land use (Fig.3). Although there are large error bars, it is clear that some land uses, such as storage and manufacturing, are considerably warmer than low density residential areas and farmland. ![HUI][1] [1]: https://edxuploads.s3.amazonaws.com/14568346515687121.png **Figure 1** - Urban Heat Island in Greater Manchester. Difference in temperature between the wide Greater Manchester urban area and its more rural surrounding. ![HUI][2] [2]: https://edxuploads.s3.amazonaws.com/14568346758008052.jpg **Figure 2** - Urban Heat Island in Greater Manchester. Difference in temperature *within* the urban area of Greater Manchester. ![Error bars][3] [3]: https://edxuploads.s3.amazonaws.com/14568346873548052.gif **Figure 3** - Relationship between temperature and land use. **3. Which are the measures you would propose?** There are different measure that one could put in place to reduce the UHI effect. Examples are provided below: 1. *Use of high albedo coatings on roofs and walls* - Application of albedo coating (cool coatings) on roofs of high rise buildings could mitigate glare and effect of reflected radiation experienced by lower storey buildings. 2. *Green roofs and green walls* - Green walls would be an excellent means to shade the walls and mitigate storage of heat in such building elements of high thermal mass. Green roofs may also result in sky gardens / green area that the micro-community of the building can enjoy. 3. *Creation of void decks* - Enhancing wind flow in urban canyon would create better urban ventilation. Creation of void decks at ground level and/ or at mid height of high rise buildings could provide unhindered movement of wind through buildings and urban canyon. 4. *Urban greenery* - Introducing urban greenery in the form of parks or planting trees along the roadside or near buildings can provide excellent shading and reduce heat gain by the building fabric. 5. *High albedo pavements* - High albedo pavements (for example, white concrete pavements) can be implemented which would mitigate high sensible heat buildup in case of otherwise dark asphalt pavements. 6. *Orientation, shape of building and effective wind paths* - Studies would be implemented to assess what are the factors in the shape and orientation of buildings that allow for a better ventilation and minimize the heat stored within the structures. **4. Is UHI effect concerning policy making in your area?** I am not aware of any policy in the area of Manchester that specifically addresses the UHI effect. There exist however studies showing how Green Infrastructure (GI) would ameliorate the effects of the UHI in Greater Manchester. In particular Gill et al. (2007) suggested that increasing the area of GI in Greater Manchester by 10% (in areas with little or no green cover) would result in a cooling by up to 2.5° C under the high emissions scenarios based on UKCP02 predictions. The study suggested that GI could reduce the impact of higher temperatures in different ways: - Trees and shrubs provide protection from both heat and UV radiation by direct shading (both of buildings and outdoor spaces). - Evapotranspiration reduces the temperature in the area around vegetation by converting solar radiation to latent heat. - Lower temperatures caused by both evapotranspiration and direct shading lead to a reduction in the amount of heat absorbed (and therefore emitted) by low albedo man-made urban surfaces (Dimoudi and Nikolopoulou, 2003). A more recent pubblication (Kazmierczak, 2012) reports on a risk-response case study for heat and social vilnerability in Greater Manchester. As for today, however, no specific policy have been implemented to address the UHI effect.