Assessing the impact of green roof on the urban heat island using satellite images: A case study of Washington D.C.
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Changing the urban environment by replacing vegetated surfaces with low albedo materials is one of the reasons for increasing temperatures in the urban environment and consequently is one of the key causes of the urban heat island effect. In urban areas, building roofs occupy a large portion of the surface area and green roofs and cool roofs are claimed to be a key approach to mitigate urban heat. Green roofs could reduce the roof top surface temperature as well as their ambient air temperature. In this study, I used satellite images to analyze the temperature of green roof buildings in Washington D.C. For the first objective of this study, I used Landsat 8 TIRS images to provide the Intra-Urban Heat Island (IUHI) pattern for Washington D.C. and performed a t-test to compare the temperatures of green and conventional roofed buildings. The result of the analysis confirms that green roofs are significantly cooler than conventional roofs. For the second objective, I used 2-way ANOVA to find the month(s) where installing green roofs had the highest impact on ambient temperature. The findings show that green roofs have cooler temperatures than conventional roofs in the warm months of the year. I then used post-treatment analysis to compare the rooftop temperature before (2009) and after green roof installation (2019). The result of this test did not confirm the hypothesis of temperature reduction due to green roof installation over the 10 year period. This may be partly attributable to the small number of green roofs in 2009. Lastly, I made two scenarios of installing green roofs on thousands of buildings citywide. The result of the third analysis shows that after hypothetically green roof installation, the impervious surface temperature in warm months of the year is significantly cooler than before green roof installation. Therefore, this research is one of the first of this kind of study on green roofs and confirms the benefit of installing green roofs in reducing temperature over rooftops.