Urban Heat Release

The Heat Wave is a disaster that affects many millions of people worldwide. The higher temperatures experienced in urban areas compared to the surrounding countryside has enormous consequences for the health and wellbeing of people living in cities. The increased use of manmade materials and increased anthropogenic heat production are the main causes of the UHI. This has led to the understanding that increased urbanisation is the primary cause of the urban heat island. The UHI effect also leads to increased energy needs that further contribute to the heating of our urban landscape, and the associated environmental and public health consequences. Pavements and roofs dominate the urban surface exposed to solar irradiation. Asphalt Concrete (AC) is one of the most common pavement surfacing materials and is a significant contributor to the UHI. Densely graded AC has low albedo and high volumetric heat capacity, which results in surface temperatures reaching upwards of 60 °C on hot summer days. Cooling the surface of a pavement by utilizing cool pavements has been a consistent theme in recent literature. Cool pavements can be reflective or evaporative. However, the urban geometry and local atmospheric conditions should dictate whether or not these mitigation strategies should be used. Otherwise both of these pavements can actually increase the UHI effect. Increasing the prevalence of green spaces through the installation of street trees, city parks and rooftop gardens has consistently demonstrated a reduction in the UHI effect. Green spaces also increase the cooling effect derived from water and wind sources. The UHI effect has significant consequences for the liveability in our cities, and is the source of a significant number of environmental problems in urban areas. The warming effect of urbanisation has critical impacts on health and wellbeing, as well as human comfort and the local atmosphere. Various consequences associated with the UHI effect; these include: • Increased cooling energy usage and associated costs; • Significant increases in peak energy demand; • The formation of large amounts of smog and air pollutants, and a resulting degradation in the quality of air; • Increased thermal stress on residents and the public; • Strong impact on urban ecosystems; • A living environment that is significantly degraded; and • A significantly increased level and risk of morbidity or illness due to heat. When heat waves hit, people start looking for anything that might lower the temperature. One solution is right beneath our feet: pavement. Research shows that building lighter-colored, more reflective roads has the potential to lower air temperatures by more than 2.5 degrees Fahrenheit (1.4 C) and, in the process, reduce the frequency of heat waves by 41% across U.S. cities. But reflective surfaces have to be used strategically – the wrong placement can actually heat up nearby buildings instead of cooling things down. Why surfaces heat up All surfaces, depending on the amount of radiation they absorb or reflect, can affect air temperatures in cities. In urban areas, about 40% of the land is paved, and that pavement absorbs solar radiation. The absorbed heat in the pavement mass is released gradually, warming the surrounding environment. This can exacerbate urban heat islands and worsen the effects of heat waves. It’s part of the reason cities are regularly a few degrees warmer in summer than nearby rural areas and leafy suburbs. Location matters But not all paved areas are ideal for cool roads. Within cities, and even within urban neighborhoods, the benefits differ. When brighter pavements reflect radiation onto buildings – called incident radiation – they can warm nearby buildings in the summer, actually increasing the demand for air conditioning. That’s why attention to location matters. Boston’s dense downtown of narrow streets has tall buildings that block light from directly hitting the pavement most hours of the day. Reflective pavement won’t help or harm much there. But Boston’s unobstructed freeways and its suburbs would see a net benefit from reflecting a large fraction of incoming sunlight to the top of the atmosphere. Using models, we found that doubling the traditional albedo of the city’s roads could cut peak summer temperatures by 1 to 2.7 F (0.3 to 1.7 C). Phoenix could reduce its summer temperatures even more – by 2.5 to 3.6 F (1.4 to 2.1 C) – but the effects in some parts of its downtown are complicated. In a few low, sparse downtown neighborhoods, we found that reflective pavement could raise the demand for cooling because of increased incident radiation on the buildings. In Los Angeles, where the city has been experimenting with a cooler coating over asphalt, researchers found another effect to consider. When the coating was used in areas where people walk, the ground itself was as much as 11 F (6.1 C) cooler, but a few feet off the ground, the temperature rose as the sun’s rays were reflected. The results suggest such coatings might be better for roads than for sidewalks or playgrounds. Cities will need to consider all of these effects. Reflective pavements are an elegant solution that can transform something we use every day to reduce urban warming. The full lifecycle emissions of roads, including the materials used in them, have to be factored in. But as cities consider ways to combat the effects of climate change, we believe strategically optimizing pavement is a smart option that can make urban cores more livable. Using Machine Learning the algorithm is developed to prioritise the road and area that requires the Reflective coating to reduce and mitigate the heat waves. This U-Net deep learning model is build using the sentinel -2 Optical Band and Landsat-8 Thermal band Satellite Images. For training the model the hottest city with highest temperature were selected such Houston (August. 2021), San Francisco(September2020), Delhi(June 2019), Sydney (January 2020), Melbourne(January 2019), Penrith(January 2020) and Bhubaneswar (April 2021). The results obtained from the model is to the priority area that should to be targeted to mitigate heat waves. The model is robust so can be applied to other cities to mitigate heat waves.

Built With

• iam
• python
• qgis
• s3
• sagemaker
• tensorflow