Effects of Densification on Urban Microclimate—A Case Study for the City of Vienna

Abstract

Climate adaptation, mitigation, and protecting strategies are becoming even more important as climate change is intensifying. The impacts of climate change are especially tangible in dense urban areas due to the inherent characteristics of urban structure and materiality. To assess impacts of densification on urban climate and potential adaptation strategies a densely populated Viennese district was modeled as a typical sample area for the city of Vienna. The case study analyzed the large-scale densification potential and its potential effects on microclimate, air flow, comfort, and energy demand by developing 3D models of the area showing the base case and densification scenarios. Three methods were deployed to assess the impact of urban densification: Micro-climate analysis (1) explored urban heat island phenomena, wind pattern analysis (2) investigated ventilation and wind comfort at street level, and energy and indoor climate comfort analysis (3) compared construction types and greening scenarios and analyzed their impact on the energy demand and indoor temperatures. Densification has negative impacts on urban microclimates because of reducing wind speeds and thus weakening ventilation of street canyons, as well as accelerating heat island effects and associated impact on the buildings. However, densification also has daytime cooling effects because of larger shaded areas. On buildings, densification may have negative effects especially in the new upper, sun-exposed floors. Construction material has less impact than glazing area and rooftop greening. Regarding adaptation to climate change, the impacts of street greening, green facades, and green roofs were simulated: The 24-h average mean radiant temperature (MRT) at street level can be reduced by up to 15 K during daytime. At night there is only a slight reduction by a few tenths of 1 K MRT. Green facades have a similar effect on MRT reduction, while green roofs show only a slight reduction by a few tenths of 1 K MRT on street level. The results show that if appropriate measures were applied, negative effects of densification could be reduced, and positive effects could be achieved.

Solar Irradiance Reduction Using Optimized Green Infrastructure in Arid Hot Regions: A Case Study in El-Nozha District, Cairo, Egypt

“…The evapotranspiration effect moisturizes the space when trees are well-irrigated and appropriately selected [15], and reduces the temperature by up to 5%. Not only trees, but also grass and other vegetative materials can attenuate the temperature by 3%, when compared to barren areas.…”

A Review of How Building Mitigates the Urban Heat Island in Indonesia and Tropical Cities

“…An intense urbanization process in the 20th century led to pollution-related problems and temperature increases in cities, resulting in a UHI [16]. Urban areas with dense populations and built-up areas are more likely to suffer from climate change, since natural surfaces are mostly replaced by sealed surfaces and construction sites [1,4,19]. Furthermore, UHI intensities are affected by factors such as wind speeds, cloud cover, season, city size, and time of day [4].…”

“…Material in urban areas absorbs solar and infrared radiation, and in turn the accumulated heat is dispersed in the atmosphere, raising the ambient temperature [39]. Specifically, roofs are envelope components that are capable of reducing indoor temperature and providing significant energy savings in air-conditioned buildings by incorporating advanced solutions such as cool roofs and green roofs [19,39]. Approximately 20-25% of the urban surface area is covered by roofs of buildings [39].…”

“…When window areas are not shaded by external shading devices, the window size has a greater effect than thermal mass. A building's height should be considered in relation to shading of south-and west-facing facades through facade greening and trees, shading of rooftop extensions, and the correct orientation of buildings and streets to reduce solar irradiation and improve natural ventilation [19]. Wind directions are to be considered when planning building orientation and design [19].…”

“…A building's height should be considered in relation to shading of south-and west-facing facades through facade greening and trees, shading of rooftop extensions, and the correct orientation of buildings and streets to reduce solar irradiation and improve natural ventilation [19]. Wind directions are to be considered when planning building orientation and design [19]. Evaluation of individual wind comfort and microclimate must be required [19].…”