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.

Global increase of urban population has brought about a growing demand for more dwelling space, resulting in various negative impacts, such as accelerated urbanization, urban sprawl and higher carbon footprints. To cope with these growth dynamics, city authorities are urged to consider alternative planning strategies aiming at mitigating the negative implications of urbanization. In this context, the present contribution investigates the potential of urban densification to mitigate the heat island effects and to improve outdoor thermal conditions. Focusing on a quite densely urbanized district in Vienna, Austria, we carried out a set of simulations of urban microclimate for pre- and post-densification scenarios using the parametric modelling environment Rhinoceros 3D and a set of built-in algorithms in the Rhino’s plug-in Grasshopper. The study was conducted for a hot summer period. The results revealed a notable solar shielding effect of newly introduced vertical extensions of existing buildings, promoting temperature decrease and improved thermal conditions within more shaded urban canyons and courtyards. However, a slight warming effect was noted during the night-time due to the higher thermal storage and lower sky view factor.

Urban agglomerations show different development patterns and stages. Here, we describe, discuss and compare urban agglomerations in different continents. The introduction section gives a general overview of specific issues of urban agglomerations. Different characteristics in Europe, Asia and America are discussed as experienced by the article’s co-authors, living in or working for urban agglomerations in these continents. First, the history of urbanization and agglomeration evolvement is described, then patterns, functional structures and relations, drivers as well as social and demographic characteristics are discussed (e.g. migration, aging, household structure, housing patterns, workplaces, etc.). Transportation infrastructure (roads, public transport systems) is also addressed as trigger for spatial dynamics causing certain effects (floor space, office and apartment rents releasing urban sprawl or hyper-densification), as well as gentrification. Further topics are urban governance and its impact on agglomeration development. Recent state and future trends will be debated, if important. A conclusion section summarizes the comparison of state, dynamics, drivers and trends.

This paper deals with climate change mitigation and addresses waste heat reuse as a measure which is until now considered only to a limited extent. The City of Vienna serves as a case study to explore potentials to improve the urban heat supply using waste heat as an additional energy source. As no observation data about waste heat and detailed heating demand is available, this data is derived from proxy data for estimating waste heat reuse potential and residential heating demand patterns. Heat requirements for manufacturing and service provision is explored and, based on the distribution of the companies within the city, mapped as waste heat sources. Employees per company serves as proxy data to allocate the heat volume. Waste heat share and temperature ranges is reviewed from literature. Heating demand is mapped based on floor space of the buildings by age class and building type. Merging supply and demand maps allows to quantify the residential heating demand coverage through local waste heat in the potential supply areas within different distance ranges and housing density classes. In high density housing areas, only a small share of the demand can be covered by waste heat supply even within 250 m distance from sources due to few companies which could provide waste heat. In medium to low density housing areas in Vienna’s outer districts with more industry, a higher share of residential heating demand near the sources can be covered by waste heat within a 250 m distance. Within a 500 m distance, around half of the residential heating demand can be covered only in low density housing areas near the waste heat sources.