Our cities will feel the heat in a changing climate (7831)
Cities are generally warmer than their rural surrounding. The Urban Heat Island phenomenon is responsible for this. The urban heat island (UHI), is a result of the high heat storage capacity of concrete and bitumen as well as the generally low albedo of urban surfaces. Vegetation in contrary stores much less energy and additionally reduces temperature due to evaporative cooling during transpiration. The urban heat island effect contributes towards increasing energy for cooling in cities, however in winter it can reduce energy consumption due to less heating demand. An increase in energy use from fossil fuel sources leads to increased GHG emissions, so any means of reducing the strength of the UHI in times of cooling demand has important energy and climate ramifications.
The current state of the temperature distribution in the Adelaide Central Business District (CBD) and its surrounding parkland belt is evaluated by the deployment of 20 temperature sensors since 2010. The observations exhibit a maximum temperature difference between CBD and parkland of 6°C with an average of 1.5°C. The maximum occurs around sun rise. The UHI is more intense in winter than in summer. The effect is most pronounced during clear and calm nights and the observed temperature difference vanishes above wind speeds of 8m/s for both clear and cloudy conditions. Daytime differences sharply decrease at temperatures above 17°C,. At night, even in cases with ambient air temperature more than about 27°C, the parks are cooler by about 2°C on average.
A micro-scale urban model was employed to study the individual street level variations due to surrounding building height and the effect of green spaces. The study of hot spot locations in the city with current and future temperature distributions and building height variations displays changes in the wind tunnel effect at street level, heat storage over the day and heat release from surface and buildings during night time. The change in temperature depending on the height variation is in excess of 1°C. This in connection to the projected temperature increase due to climate change has major implications to energy use and carbon emissions in the future. Green spaces clearly augment the temperature field in the vicinity. Depending on the synoptic situation UHI mitigation can be achieved by placing green spaces close to hot spot locations.