b'MUDD 24 URBAN NETWORKS|URBAN GATEWAYSThere is a need to develop more efficientnatural soil decreases the evaporation400 major cities around the world. mitigation technologies able to furtherprocesses and results in higher ambientWestern Sydney suffers from a serious decrease the ambient temperature andtemperatures. overheating problem during summer. Data counterbalance local climate change. Thiscollected from a network of 25 meteorological goal may be achieved either by developing(b) Anthropogenic heat released bystations operated by UNSW in combination materials able to present and keep theirheating systems, air conditioning, cars,with the existing Bureau of Meteorology (BOM) surface temperatures below the ambient, orindustry and the other combustionstations, reveal that the intensity of urban by large scale dissipation of the excess urbansystems. overheating may exceed 9-10C compared heat to a low temperature heat sink, or throughto the Eastern Suburbs. During the peak technologies combining both principles. (c) Radiative Geometry of Canyons.summer period, ambient temperatures in Because of the specific geometry of theWestern Sydney may be 7-8C higher than UHI is the most documented phenomenon ofurban canyons, the infrared radiationat Observatory Hill and the airport. A recent climate change. It was reported for the first timeemitted by buildings, streets andanalysis, of the relevant climatic data (Figure at the beginning of the 19th century in Londonpavements cannot escape. It is reflected2) shows that during the peak summer period (Howard 1833, pp.2-3). It is related to theand absorbed by the canyon surfacesthe daytime ambient temperature in Western development of higher ambient temperaturesand contributes to a more positive thermalSydney may be 1 to 10C higher than at the in the dense central urban zones comparedbalance in the canyons. In parallel,reference climatic station at Observatory Hill. to the surrounding suburban and rural areasbecause of the multi-reflections in the (Figure 1).canyon, a high part of the initially reflectedHigher ambient temperatures in Western solar radiation is absorbed increasing theSydney persist during the whole summer. This surface temperature of the vertical wallsis clear once the distribution of the cooling and the other surfaces. degree days is calculated for the various zones of Sydney. As shown in Figures 3 and (d) Urban Greenhouse Effect. Because4, the annual cooling degree days in Western of the high concentration of atmosphericSydney are almost 80-100% higher than at pollutants, part of the emitted infraredObservatory Hill or in the coastal area. Such radiation from the ground surfaces isa tremendous increase in cooling degree days reflected back to the earths surface,has a very significant impact on the cooling while the emitted infrared radiation by theenergy demand in the area, imposing a serious Figure 1. Urban Heat Island: Ambient Temperaturepollutants is higher.penalty on the local population. The recent Profile in Urban, Suburban and Rural Areas. study by the Cooperative Research Centre Source: Royal Meteorological Society (e) Reduced Turbulent Transfer of Heatfor Low Carbon Living and of Sydney Water, from within streets. shows that due to substantial overheating, the The phenomenon is the result of the positiveenergy consumption of typical commercial and energy balance of the urban areas that(f) Reduction of Evaporating Surfacesresidential buildings in Parramatta is almost increases the ambient temperatures. Severalin the urban environment that decreases50-70% higher than in the coastal area of the parameters influence and determine thethe latent and increases the sensible heatcity. magnitude of the phenomenon. Oke (1997)load.has summarised the most important factors 9 influencing Urban Heat Island development:Higher urban temperatures increase energy (a) Thermal Properties of the Materialsconsumption for cooling, deteriorate the in the Urban Environment. Most of theoutdoor and indoor thermal comfort conditions, materials used in buildings and openraise the concentration of harmful pollutants spaces present a high absorptivity to solarlike the tropospheric ozone, have a serious radiation. This results in higher surfaceimpact on human health and well-being, and temperatures and important heat storageincrease the ecological footprint of cities. To in cities. The stored heat is then releaseddocument the amplitude and the characteristicsFigure 2. Urban Heat Island measured at the Olympic to the atmosphere through convectionof the Urban Heat Island, measurements haveVillage, City of Parramatta as a function of day time and radiation processes. In parallel, thebeen performed in hundreds of cities, theambient temperature, compared to Observatory Hill, replacement of the vegetation and of thephenomenon is fully documented in more thanSydney.MUDD 24 - Urban Gateways | Urban NetworksINTRO 8pt.indd 10 26/11/2019 4:11:24 PM'