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INTRODUCTION WHAT IS THE URBAN HEAT ISLAND?  CONSIDERATIONS URBAN HEAT ISLAND (UHI) MITIGATION AND ADAPTATION ALBEDO ENHANCEMENT SIMPLIFIED SENSIBLE HEAT REDUCTION SIMPLIFIED CREATING COOL MICRO-CLIMATES  UNSOLVED QUESTIONS 
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INTRODUCTION


The Climate Change is a very abstract, large and remote phenomenon with 50 to 100 year horizon what makes it difficult to act on it with any sense of urgency. In many climate zones, the Urban Heat Island (UHI) is a more immediate, local and palpable challenge, with a 5 to 10 year horizon. Strategies to mitigate and adapt to the Urban Heat Island Effect are almost identical to the challenge of global climate change.


In a sense the UHI can be invoked as an effective motivator and mobilizers of behavioural and physical change in many climate zones of the world. Direct interventions tend to have quicker and more tangible results, so they are typically more satisfying and motivating.


The UHI brings increasingly uncomfortable air temperatures in cities and thereby diminish their appeal. People are likely more encouraged to migrate to suburban and rural areas. This migration of urban residents - with their life styles - to the of suburban an rural areas, will be -in equivalent- more wasteful, energy-consumptive and carbon-intensive.


 

 

WHAT IS THE URBAN HEAT ISLAND?


UHI can be conflated and confused with global CC. There is considerable overlap, but also consequential difference.  UHI is a local phenomenon. And the increase of local  is not from GHGs trapping heat in the atmosphere, but from a local increase in sensible heat.

 

Sensible heat comes from two sources


Both heat sources raise the average urban temperature higher than the surrounding suburbs and rural countryside or wilderness


The rural to urban temperature gradient can be 4 to 6 or more degrees Celsius. During heat waves temperature differences between city center(s) and countryside may double.





CONSIDERATIONS


Why is it desirable for more people to live in cities? Compared to their suburban and rural counterparts, urban residents have smaller energy, carbon and ecological footprints, which is the equivalent area needed to provide the resources they consume and to absorb their wastes.




URBAN HEAT ISLAND (UHI) MITIGATION AND ADAPTATION STRATEGIES


Primarily there are three ways to mitigate and adapt to UHI in order to achieve urban cooling.


1. Albedo Enhancement (lighter-coloured roofs and pavement)

2. Sensible Heat Reduction (hot gases from tailpipes and chimneys)

3. Cool Micro-climates (trees and vegetation to shade, filter, cool the air, etc., while providing scale, beauty and other amenities)


On top of their urban cooling benefits, all three of these Lean strategies are proven antidotes to global Climate Change (CC). They directly adapt to CC by tempering increasing global air temperatures and simultaneously and indirectly helping with mitigating these increases. They are achievable, easily understandable strategies that lend themselves to distributed, by democratic action at the local scale.




ALBEDO ENHANCEMENT SIMPLIFIED


More reflective surfaces, especially horizontal ones like roofs and pavement, are very effective ways to bounce back solar radiation before it heats up the surface and nearby air.


Albedo is measured by the Solar Reflectivity Index (SRI). The SRI indicates the percentage of solar radiation that is bounced back through the earth’s atmosphere into outer space before it heats up any mass or air.


White and light coloured horizontal surfaces with a high SRI – primarily roofs and pavement–

 



SENSIBLE HEAT REDUCTION SIMPLIFIED


Reduce the local production and release of sensible heat into the urban environment, in the form of hot air and other gases. This means decreasing the combustion of hydrocarbon fuels in both motor vehicles, power plants and industrial processes.


A effective way to reduce tailpipe emissions of heat is a better organized and facilitated public transport system that foresees in the need of urban transit.




CREATING COOL MICRO-CLIMATES


This cooling is achieved primarily with plant materials, especially shade trees.

Trees along streets, roads and in parking lots constitute a large and particularly effective urban tree canopy.

The list of the environmental contributions of vegetation is long: trees provide cool shade, evaporation-transpiration that cools and moistens the air, particulate pollution filtration, soil retention, water retention, while absorbing sound and shaping public space.




UNSOLVED QUESTIONS

The direct and indirect relationship between UHI and CC is very complex and not fully understood yet. The interaction between the Urban Heat Island’s  micro climate with that of the surrounding suburbs an rural areas. Complicating factors on determination of the air temperature would be te interaction between albedo-increasing cloud covers and surface cooling rains. And many other parameters.



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MISERY INDEX

Findings and research already indicate that perceived temperature is increasing for most world regions. As a result, higher mortality rate is to expected.

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THE IMPORTANCE OF ATMOSPHERIC CONVECTION


Convection within the troposphere is critical in order to prevent global warming

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ALBEDO SIMPLIFIED


Albedo is measured by the Solar Reflectivity Index (SRI). The SRI indicates the percentage of solar radiation that is bounced back through the earth’s atmosphere into outer space before it heats up any mass or air.


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AIR POLLUTION


Air pollution consist of chemicals, particulate matter or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural or built environment. There is great concern over deteriorating air quality as it can contribute to many health problems in our community……


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MORTALITY

Air pollution is one of the major environ-mental causes of premature mortality.

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THE URBAN HEAT ISLAND

“If you can't take the heat, get out of the city.”