At the beginning of the 21st century, the phenomenon of shrinking cities was widely discussed across Europe. Most European countries saw an increasingly ageing population and an internal migration from underdeveloped to more competitive locations. Since the turn of the century, and in contrast to the past, a great deal has been written about the causes and impacts of shrinkage, as well as about policies and planning strategies. However, the state of knowledge in a cross-national comparative perspective is rather poor because, to date, studies have basically analysed large cities and empirical evidence hardly shifts attention to the contextual influence on local dynamics. Against this background, this paper fills the gap between macrotheoretical conceptualisation and empirical observation by testing a heuristic model of urban shrinkage encompassing the whole range of cities in Europe. The paper questions to what extent urban shrinkage represents a broader trend in Europe in terms of both duration and distribution, and aims to investigate the influence of economic and demographic drivers on the non-linear evolution of shrinking cities in Europe. Thereby, the spatial distribution of different trajectories of shrinking cities in urban Europe in the period from 1990 to 2010 will be presented in a comprehensive survey which reveals that 20% of European cities experienced shrinkage between 1990 and 2010, whereas 883 cities face recent shrinkage.

After several decades, an increasing number of European cities have been experiencing population growth after a longer phase of decline. This new growth represents not just a quantitative phenomenon but also has qualitative implications for the urban space and the built environment. A juxtaposition of re- and de-densification, as well as changes in land use, in the form of a small-scale spatial mosaic, can be observed. A crucial factor for estimating the relationship between the built environment and demand for it is population density. Increasing population densities may put pressure on sustaining a certain quality of life and on ecological recovery spaces. In this vein, an indicator concept for re- and de-densification will be applied to the city of Leipzig, one of the most illustrative examples of a regrowing city, in order to shed light on the complex relationship between changing human housing demands and their impact on land use. The concept involves measuring population density. Our study has demonstrated that, although similar density changes can be observed in different periods in different parts of the city, they are dominated by different drivers, leading to the formation of different spatial patterns. The results of our study emphasise that regrowth should be understood as a distinctive process because it is distributed very heterogeneously within the city area, with a variety of spatial effects and impacts. The concept allows us to draw conclusions about processes that mitigate, drive or reinforce regrowth, and therefore contributes to a better understanding of this phenomenon and its implications for land use.

Urban growth in and around European cities affects multiple aspects of the environment including green spaces. On the one hand, many cities struggle with environmental problems, overcrowding and overuse resulting from high population densities. On the other hand, high densities result in better access to public green spaces, effective public transport, or less demand for resources. Consequently, finding a balance between density and high liveability in a green and sustainable urban environment is a major challenge for urban planning. Although many studies report and discuss the provision of green spaces in European cities, they fail to relate green space provision to the potential demand by urban dwellers, and to the extent differences can be detected between types of green. Against this background, this paper develops a systematic understanding of green space supply and its relation to the residential density of cities. In so doing, it detects turning points of green space supply in 905 European cities. The results show that green space supply is sensitive to the type of green space, population size and location of cities. Particularly the relation between residential density and the supply with urban green spaces covering parks, public gardens or cemeteries, indicate turning points: at certain residential densities the urban green space supply is decreasing. At a certain residential density, the urban green space supply is highest and cities have a high potential to optimize the balance between sustainability and liveability. However, there is no single optimal residential density. Rather, turning points are different between cities of different density and location in Europe and between different types of neighborhoods within cities. Therefore, different optimum values need to be defined sensitive to these characteristics. For most of the European cities, a decrease of population or built-area cannot be expected in the future. In this situation, the approach to identifying the turning points for green space supply as presented in this paper can be used as a comparative method. This informs green space policies for defining acceptable densities of urban development and corresponding standards for the provision of urban green space.

Changes in urban residential density represent an important issue in terms of land consumption, the conservation of ecosystems, air quality and related human health problems, as well as the consequential challenges for urban and regional planning. It is the decline of residential densities, in particular, that has often been used as the very definition of sprawl, describing a phenomenon that has been extensively studied in the United States and in Western Europe. Whilst these studies provide valuable insights into urbanization processes, only a handful of them have reflected the uneven dynamics of simultaneous urban growth and shrinkage, using residential density changes as a key indicator to uncover the underlying dynamics. This paper introduces a contrasting analysis of recent developments in both de- and re-concentration, defined as decreasing or increasing residential densities, respectively. Using a large sample of European cities, it detects differences in density changes between successional population growth/decline. The paper shows that dedensification, found in some large cities globally, is not a universal phenomenon in growing urban areas; neither the increasing disproportion between a declining demand for and an increasing supply of residential areas nor actual concentration processes in cities were found. Thus, the paper provides a new, very detailed perspective on (de)densification in both shrinking and growing cities and how they specifically contribute to current land take in Europe.