The temperature of urban areas can be significantly higher than that of the surrounding rural areas. This fact is known as the "Urban Heat Island" effect.

Is this Global Warming?

• No, this is a separate phenomenon where cities are 6-8°F warmer than surrounding rural areas. Global warming however could increase the impact of urban island felt in cities in the summer months.

Factors work to promote a heat island.

• Concrete and man made surfaces

• Less water in the soil and environment

• Excess energy from buildings

What is an Urban Heat Island?

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Causes

Difference b/w Black and White Materials

Causes

• The main cause of the UHI effect is from the modification of land surfaces, which use materials that effectively store short-wave radiation. Waste heat generated by energy usage is a secondary contributor. change in the energy balance.

During the day in rural areas, the solar energy absorbed near the ground evaporates water

from the vegetation and soil(evapotranspiration). Thus, causes

evaporative cooling. In cities, where there is less vegetation, the

buildings, streets and sidewalks absorb the majority of solar energy input. UHIs have been

indirectly related to climate change due to their contribution to the greenhouse effect, and

therefore, to global warming.

Tar, asphalt, brick and concrete absorb insolation and release it as heat, rather than

reflecting it (without heat) like soil does.

The principal reason for the nighttime warming is that buildings block surface heat from radiating into the relatively cold night

sky.

Effects of UHI• The extra heat from urban environments can cause

extreme weather and climatic events such as storms, hurricanes, and floods. Warmer air can hold more water and moisture, which results in more precipitation. For every 1°F warming, atmospheric water vapor increases 3-4%. Urban heat islands can cause up to 15°F of warming, which can increase atmospheric water vapor by more than 50%!

Extreme Weather

• Every 1°C increase in air temperature, there is a 5-10% increase in electricity demand this energy demand need more fossil fuels and more pollution.

Heat islands can exacerbate the health risk of heat waves during the summer, difficulty in breathing in olds , heat craps, and heat strokes. Impact on ecosystems, the atmosphere, and people.

Mitigation 1.Building green roof/wall

2.Create more city parks 3.Covers roofs and roads with light colored materials to Increase the Albedo 4.Tree Plantation and Preservation 5. Plant Trees For Energy Efficiency

6. Low Impact Development Techniques

Green roofs can be installed on a wide range of buildings, from industrial facilities to private residences

Green Roof• A green roof, or rooftop garden, is a

vegetative layer grown on a rooftop. It provides shade and remove heat from the air through evapotranspiration, reducing temperatures of the roof surface and the surrounding air. conventional rooftop can be up to 90°F (50°C) warmer.

Green roof Vs. Conventional

Green Walls

Mitigation• By increasing the albedo, or solar reflectance (SR), of

surfaces such as roofs, pavements, and cars, the surfaces absorb less solar heat and thus transmit less heat back into the environment. This process, called "negative radioactive forcing," effectively cools the environment and offsets substantial quantities of greenhouse CO2.

Mitigation

• Tree Strategies for Heat Island Reduction “The net cooling effect of a young, healthy tree is equivalent to 10 room-size air conditioners operating 20 hours a day.” —U.S. Department of Agriculture

• “Trees properly placed around buildings can reduce air conditioning needs by 30 percent and can save 20-50 percent in energy used for heating.” – US Forest Service

Jazzak Allah