Taking Stock of Built Environment Stock Studies: Progress and Prospects.

Built environment stocks (buildings and infrastructures) play multiple roles in our socio-economic metabolism: they serve as the backbone of modern societies and human well-being, drive the material cycles throughout the economy, entail temporal and spatial lock-ins on energy use and emissions, and represent an extensive reservoir of secondary materials. This review aims at providing a comprehensive and critical review of the state of the art, progress, and prospects of built environment stocks research which has boomed in the past decades. We included 249 publications published from 1985 to 2018, conducted a bibliometric analysis, and assessed the studies by key characteristics including typology of stocks (status of stock and end-use category), type of measurement (object and unit), spatial boundary and level of resolution, and temporal scope. We also highlighted the strengths and weaknesses of different estimation approaches. A comparability analysis of existing studies shows a clearly higher level of stocks per capita and per area in developed countries and cities, confirming the role of urbanization and industrialization in built environment stock growth. However, more spatially refined case studies (e.g., on developing cities and nonresidential buildings) and standardization and improvement of methodology (e.g., with geographic information system and architectural knowledge) and data (e.g., on material intensity and lifetime) would be urgently needed to reveal more robust conclusions on the patterns, drivers, and implications of built environment stocks. Such advanced knowledge on built environment stocks could foster societal and policy agendas such as urban sustainability, circular economy, climate change, and United Nations 2030 Sustainable Development Goals.

Sinks as limited resources? A new indicator for evaluating anthropogenic material flows.

Besides recyclables, the use of materials inevitably yields non-recyclable materials such as emissions and wastes for disposal. These flows must be directed to sinks in a way that no adverse effects arise for humans and the environment. The objective of this paper is to present a new indicator for the assessment of substance flows to sinks on a regional scale. The indicator quantifies the environmentally acceptable mass share of a substance in actual waste and emission flows, ranging from 0% as worst case to 100% as best case. This paper consists of three parts: first, the indicator is defined. Second, a methodology to determine the indicator score is presented, including (i) substance flows analysis and (ii) a distant-to-target approach based on an adaptation of the Ecological Scarcity Method 2006. Third, the metric developed is applied in three case studies including copper (Cu) and lead (Pb) in the city of Vienna, and perfluorooctane sulfonate (PFOS) in Switzerland. The following results were obtained: in Vienna, 99% of Cu flows to geogenic and anthropogenic sinks are acceptable when evaluated by the distant-to-target approach. However, the 0.7% of Cu entering urban soils and the 0.3% entering receiving waters are beyond the acceptable level. In the case of Pb, 92% of all flows into sinks prove to be acceptable, and 8% are disposed of in local landfills with limited capacity. For PFOS, 96% of all flows into sinks are acceptable. 4% cannot be evaluated due to a lack of normative criteria, despite posing a risk for human health and the environment. The examples demonstrate the need (i) for appropriate data of good quality to calculate the sink indicator and (ii) for standards, needed for the assessment of substance flows to urban soils and receiving waters. This study corroborates that the new indicator is well suited as a base for decisions regarding the control of hazardous substances in waste and environmental management.

Site-specific dataset of mining and metallurgical residues for resource management.

This geospatial dataset provides a compilation of findings from an evidence-based review of site-specific resource assessments of mining and metallurgical residues. Information pertaining to location, target material, geological knowledge, extractability, resource classification and stakeholder perspectives was collected from publicly available reports, articles, academic theses, and databases. The dataset includes 44 relevant data attributes from 64 mining and metallurgical sites in 27 countries. Resource classification is available for 38 sites. The dataset can be used by evaluators of recovery projects, authorities that provide permits, as well as by decision makers in support of developing regulatory policies. The dataset facilitates future addition of sites by the research community and can be further used as a starting point to bridge the estimates on recoverable quantities to the United Nations Framework Classification (UNFC). The UNFC is a universally applicable scheme for the sustainable management of all energy, primary and secondary mineral resources. Its use is stimulated by the European Commission and is intended to be adopted by geological surveys to harmonize the data on the availability of primary and secondary raw materials in Europe in future.

Data description of "building age map, Vienna, around 1920".

Building age maps inventory the construction dates of buildings. While many cities routinely map the construction dates of present building stocks, building age maps of the distant past are mostly not available. An exception is the building age map of Vienna around 1920. It covers about 80% of the building footprint area within the city boundary in 2020 and is available in analog format only. This impedes spatial analysis of the building stock in the past and the production of time-series data for the spatio-temporal analysis of building stock developments over the last 100 years. To create the digital map, we manually vectorized 80,640 building footprints from 134 historical map sheets and assigned construction dates (i) from the analog building age map by digitizing color-encoded thematic information and (2) from a historical building registry by matching building address. From the analysis of the generated dataset we infer that the total building footprint area was 2,279 hectares. The classification of the building footprint areas by construction date shows that 14% of the buildings were older and 63% were younger than 70 years. The remaining 23% lack construction period assignments due to missing data. The resulting dataset underwent technical quality checks and external data sources were used to validate the building counts, the building presence around 1920 and the construction dates of buildings. During course of validation, we critically discuss data quality and recommend improvements. We see a practical reuse value of the data for the spatio-temporal analysis of urban buildings stocks, which facilitates urban history research as well as resource and environmental management in the city of Vienna.

Building schematic of Vienna in the late 1920s.

Urban archives provide rich information on historical data. To a large extent, these data are not available in machine-readable format and therefore not linkable with other datasets. The "Häuser-Kataster der Bundeshauptstadt Wien" is a building schematic for the city of Vienna for the end of the 1920s. While this schematic was used as a knowledge base for real estate and finance business about 100 years ago, it has been used in the 2000s to manually map the historic building periods by property. We use the analog version and produced a machine-readable version to assign the historic addresses, building periods and number of floors to a building stock model down the road. The dataset has been complemented with codes of cadastral communities from the late 2010s to enable geotagging of the historic building data. To avoid unnecessary duplication of efforts by others and to share the dataset with urban historians and the public, we provide the dataset under creative common license.

Data description of "City boundary and urban district boundaries, Vienna, 1920".

This article presents geospatial datasets for administrative boundaries of the city of Vienna in 1920. One dataset covers the city area and another the urban districts. The boundaries were retrieved from historic analog maps that show the course of the borders at this time. GIS software was used to geocode the analog maps and construct the polygon-features for the city and 21 district areas. These datasets are useful for mapping the spatial coverage of administrative units in the 1920s and to group and analyse further historic GIS data.

The Copper Balance of Cities: Exploratory Insights into a European and an Asian City.

Material management faces a dual challenge: on the one hand satisfying large and increasing demands for goods and on the other hand accommodating wastes and emissions in sinks. Hence, the characterization of material flows and stocks is relevant for both improving resource efficiency and environmental protection. This article focuses on the urban scale, a dimension rarely investigated in past metal flow studies. We compare the copper (Cu) metabolism of two cities in different economic states, namely, Vienna (Europe) and Taipei (Asia). Substance flow analysis is used to calculate urban Cu balances in a comprehensive and transparent form. The main difference between Cu in the two cities appears to be the stock: Vienna seems close to saturation with 180 kilograms per capita (kg/cap) and a growth rate of 2% per year. In contrast, the Taipei stock of 30 kg/cap grows rapidly by 26% per year. Even though most Cu is recycled in both cities, bottom ash from municipal solid waste incineration represents an unused Cu potential accounting for 1% to 5% of annual demand. Nonpoint emissions are predominant; up to 50% of the loadings into the sewer system are from nonpoint sources. The results of this research are instrumental for the design of the Cu metabolism in each city. The outcomes serve as a base for identification and recovery of recyclables as well as for directing nonrecyclables to appropriate sinks, avoiding sensitive environmental pathways. The methodology applied is well suited for city benchmarking if sufficient data are available.

Sustainable resource use requires "clean cycles" and safe "final sinks".

In order to fulfill the objectives of environmental protection, today's focus on quantitative recycling rates must be amended by a more qualitative approach. Because modern products represent a mix of numerous and sometimes hazardous substances, ways must be explored to remove detrimental substances during recycling and to establish "clean cycles". On the one hand, such a "clean cycle" strategy will result in better recycling qualities of secondary products and less dissipation of hazardous substances during further product use. On the other hand, the elimination of hazardous substances during recycling requires sinks for the disposal of the eliminated materials. These topics are presented in general as well as by case studies. In particular, the sink issue is addressed, differentiating between sinks and final sinks and discussing the challenge to supply appropriate final sinks for all materials that cannot be recycled.