Smart environment for smart cities: Assessing urban fabric types and microclimate responses for improved urban living conditions

Urban areas are particularly vulnerable to the impacts of climate change; they are also the chosen living environment of a significant majority of Europe‘s population. Global warming increasingly influences the urban climate and affects the future health and well-being of the urban population. The urban climate is mainly influenced by the urban form and the open space structure, which significantly modify the regional climatic conditions, and thereby directly affect the (thermal) comfort of the citizens. At the same time, urban open spaces are generally becoming more important as a result of their role in helping to support sustainable urban development from an ecological, social and economic point of view. Thus the future quality of life within cities is highly dependant on the “smart” treatment of its open space structure. The objective of the present study within the ACRP 3rd call was to better understand the way in which the small scale structure of the urban fabric contributes differentially to heat island effects and other urban climate phenomena, and to use this information to develop specific strategies for counter-acting and mitigating these effects on a local basis. A major focus has been laid on the urban morphology and in particular the urban landscape, and on understanding its interaction with urban microclimate. The aim was to identify climate sensitive urban patterns – using the example of Vienna - and to suggest concrete open space design measures to counteract the overheating effect during hot summer days. On the basis of a grid used by Statistik Austria (quadrants of 500 m x 500 m) an urban fabric typology for the city of Vienna has been generated taking into account aspects of urban climate and urban structure with regard to terrain, open space and built structure, which influence the microclimatic conditions and parameters. The derived “urban fabric types” have been analysed, characterised, and a sample of the most critical types formed the basis for further investigation of potential open space design measures aimed at counteracting the overheating. This was undertaken using the microclimate simulation programme ENVI-met 4.0. The evaluation of the data generated has focused on thermal comfort and on its most relevant climate factors and has taken the form of maps, mean values and diurnal variations. Based on the evaluation of the simulation results and with regard to results of a previous project, a general catalogue of open space design measures has been compiled. Representative packages of measures have been defined for each sample quadrant, highlighting their specific conditions based on their open space patterns and climate sensitivity, and focused at obtaining the optimal influence on thermal comfort amelioration

Understanding the whole city as landscape. A multivariate approach to urban landscape morphology

The European Landscape Convention implies a requirement for signatory states to identify their urban landscapes which goes beyond the traditional focus on individual parks and green spaces and the links between them. Landscape ecological approaches can provide a useful model for identifying urban landscape types across a whole territory, but the variables relevant for urban landscapes are very different to those usually addressing rural areas. This paper presents an approach to classifying the urban landscape of Vienna that was developed in a research project funded by the Austrian Ministry for Transport, Innovation and Technology: ‘Urban Fabric and Microclimate Response’. Nine landscape types and a number of sub-types were defined, using a multivariate statistical approach which takes account of both morphological and urban climate related variables. Although the variables were selected to objectively reflect the factors that could best represent the urban climatic characteristics of the urban landscape, the results also provided a widely plausible representation of the structure of the city’s landscapes. Selected examples of the landscape types that were defined in this way were used both to simulate current microclimatic conditions and also to model the effects of possible climatic amelioration measures. Finally the paper looks forward to developing a more general-purpose urban landscape typology that allows investigating a much broader complex of urban landscape functions

Understanding the whole city as landscape. A multivariate approach to urban landscape morphology

The European Landscape Convention implies a requirement for signatory states to identify their urban landscapes which goes beyond the traditional focus on individual parks and green spaces and the links between them. Landscape ecological approaches can provide a useful model for identifying urban landscape types across a whole territory, but the variables relevant for urban landscapes are very different to those usually addressing rural areas. This paper presents an approach to classifying the urban landscape of Vienna that was developed in a research project funded by the Austrian Ministry for Transport, Innovation and Technology: ‘Urban Fabric and Microclimate Response’. Nine landscape types and a number of sub-types were defined, using a multivariate statistical approach which takes account of both morphological and urban climate related variables. Although the variables were selected to objectively reflect the factors that could best represent the urban climatic characteristics of the urban landscape, the results also provided a widely plausible representation of the structure of the city’s landscapes. Selected examples of the landscape types that were defined in this way were used both to simulate current microclimatic conditions and also to model the effects of possible climatic amelioration measures. Finally the paper looks forward to developing a more general-purpose urban landscape typology that allows investigating a much broader complex of urban landscape functions

Comparison of thermal models for ground-mounted south-facing photovoltaic technologies: a practical case study

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Application of the model ‘Heat Source’ to assess the influence of meteorological components on stream temperature and simulation accuracy under heat wave conditions

Stream temperature is one of the most important factors for aquatic organism, but also regulates drinking water quality, which are both threatened by temperature rises. Atmospheric heat fluxes are primary drivers of stream temperature changes, all of them dependent on the rivers' openness to sky.To be able to simulate stream temperature in rivers of complex terrain and shaded by riparian vegetation a deterministic model including all shading processes was used and validated for the application for Eastern Austrian lowland rivers during summer and the heat wave 2–8 August 2013. The global radiation was included as direct input, which lead to an improvement. It is shown, that both net short wave radiation and evaporation are the most influential components under heat wave conditions and that both are subject to the influence of shading by topography and vegetation. The forward propagation of measurement imprecisions of atmospheric input parameters on simulated water temperature was calculated. The total model imprecision caused by measurement errors of sky obstructing elements (+1.24/−1.40 °C) exceeds the error caused by measurement errors of meteorological input parameters (+0.66/−0.70 °C). The most important sky obstructing elements are vegetation height and vegetation density. A total model imprecision caused by measurement errors of meteorological and shading input parameters is calculated with +1.90/−2.10 °C. While the errors caused by meteorological input are expected much smaller under normal conditions, sky view reducing errors are realistic or even underestimated

The influence of riparian vegetation shading on water temperature during low flow conditions in a medium sized river

Stream water temperature limits the growth and survival of aquatic organisms; whereby riparian shading plays a key role in inhibiting river warming. This study explains the effects of riparian shading on summer water temperatures at a pre-alpine Austrian river, during heatwave and non-heatwave periods at low flow conditions. A vegetation-shading index was introduced for the quantification of riparian vegetation effects on water temperature. For maximum water temperatures, a downstream warming of 3.9 °C was observed in unshaded areas, followed by a downstream cooling of 3.5 °C in shaded reaches. Water temperature directly responded to air temperature and cloudiness. For an air temperature change of 2 °C we modelled a water temperature change of 1.3 °C for unshaded reaches, but lower changes for intensively shaded reaches. Similar daily variations at shaded reaches were up to 4 °C lower than unshaded ones. This study gives clear evidence that for a medium-sized pre-alpine river, restoration practices should consider that discontinuity of riparian vegetation should be less than 6000 m; with more than 40% dense vegetation in order to minimize water temperature increases due to unshaded conditions

Thermal conditions during heat waves of a mid-European metropolis under consideration of climate change, urban development scenarios and resilience measures for the mid-21st century

In this study we produce two urban development scenarios estimating potential urban sprawl and optimized development concerning building construction, and we simulate their influence on air temperature, surface temperatures and human thermal comfort. We select two heat waves representative for present and future conditions of the mid 21st century and simulations are run with the Town Energy Balance Model (TEB) coupled online and offline to the Weather Research and Forecasting Model (WRF). Global and regional climate change under the RCP8.5 scenario causes an increase of daily maximum air temperature in Vienna by 7 K. The daily minimum air temperature will increase by 2–4 K. Changes caused by urban growth or densification mainly affect air temperature and human thermal comfort locally where new urbanisation takes place and does not occur significantly in the central districts. A combination of near zero-energy standards and increasing albedo of building materials on the city scale accomplishes a maximum reduction of urban canyon temperature achieved by changes in urban parameters of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaptation measures show that insulation of buildings alone increases the maximum wall surface temperatures by more than 10 K or the maximum mean radiant temperature (MRT) in the canyon by 5 K. Therefore, measures to reduce MRT within the urban canyons like tree shade are needed to complement the proposed measures. This study concludes that the rising air temperatures expected by climate change puts an unprecedented heat burden on Viennese inhabitants, which cannot easily be reduced by measures concerning buildings within the city itself. Additionally, measures such as planting trees to provide shade, regional water sensitive planning and global reduction of greenhouse gas emissions in order to reduce temperature extremes are required

The influence of vegetation drought stress on formaldehyde and ozone distributions over a central European city

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