NFP 68 project: Controlling urban sprawl to limit soil consumption (SPROIL)

Since the 1950s, Switzerland has experienced a continued high growth of urban sprawl. Despite this unprecedented growth, some municipalities have very successfully managed to control urban sprawl. Overall, however, the trend has not been successfully stopped. In order to restrict the associated soil consumption, innovative instruments and measures are desperately needed. In order to develop these, it is necessary to better understand the causes and drivers of urban sprawl.

This NFP68 project aims at examining the political, planning and socio-economic factors, the so-called drivers, which have been determining urban sprawl since the 1950s. Data on urban sprawl going back to 1885 will serve as the basis for this analysis. The identified drivers will be used in spatially explicit predictive models. Thanks to these models, it will be possible to estimate future urban sprawl and soil consumption using a range of scenarios. In so doing, both developments that adhere to the principle of “business as usual” and situations that arise through the implementation of financial incentives and new planning instruments will be monitored.

Thanks to this project, it will be possible to draw up risk maps for soil consumption caused by urban sprawl. Further we will derive a set of recommendations to reduce urban sprawl. For selected communities and regions, in-depth analyses will be carried out to analyze the causal relationships between political-administrative and socio-economic conditions, planning and economic steering instruments and urban sprawl.

Methods

Module 1 Economic drivers

In module 1 the economic drivers of urban sprawl were analyzed. Therefore, an evaluation of economic drivers using municipality-level data was conducted. It was particularly the spatial signal in the urban sprawl measures, that was of major interest in the analysis. In addition, it was examined, whether a combination of structural factors and fiscal incentives may explain the structure of urban sprawl in Switzerland.<br/>

Module 2 Political and planning drivers

In module 2, the adoption of local growth-management policies was assessed based on a survey at the municipal level. In addition, it was examined to what extent local comprehensive plans have the potential to effectively steer urban development towards sustainable and compact urban forms. To this end, the policy focus and the analytical quality of 40 plans was examined with content analysis.

Module 3 Spatially explicit predictive models of urban sprawl<br/>

The knowledge from the two previous modules is input into the modeling module 3, which relates sprawl metrics to drivers and predicts sprawl under various scenarios. Building a Swiss-wide regression model at a 1ha resolution was the first task in this module. The second task consisted of a spatially explicit prediction of of urban sprawl by 2035 using allocation models. 

Results

Module 1

At the level of the municipality, soil consumption and urban sprawl is clearly correlated with economic wealth, accessibility and high shares of inbound commuters. Population growth, at least before the year 2000, is only weakly correlated and has not much predictive power. Societal developments such as a higher share of retired people or more single-person households are also rather clearly correlated with urban sprawl.

Over time, correlations between some explanatory variables and the extent of the built-up area become weaker while their correlation with the density of the built-up area grows stronger. This uncovers a temporal aspect of urbanization: municipalities that have grown in the past enter a phase of densification thereafter.

Accessibility does not only exhibit a spatially varying correlation with the extent and the density of the built-up area (that is delineated spatially by metropolitan areas) but it also has an influence on how strongly other aspects, such as tax-burden, for example, are correlated with urban sprawl.

Module 2

According to the survey, municipalities tend to adopt rather traditional and well-established regulatory and conceptual policies. Innovative instruments implemented through negotiation and incentives are less common. The planning capacity of larger municipalities allows them to implement such kinds of incentive-oriented policies more often. However, the analysis also shows that the adoption of incentive-oriented policies by small municipalities increased dramatically since 2010.

According to the analysis of local comprehensive plans, cantonal planning mandates for local comprehensive planning strongly affect the quality of comprehensive plans. They encourage the development of plans that address sustainable spatial development in a coordinated and comprehensive way.

Many comprehensive plans have a low analytical quality, since they do not provide a clear vision of the future development and don't identify the responsible actors or the time-frame for implementation. This casts doubt on the ability of adopted comprehensive plans to steer urban growth towards a sustainable spatial development.

Module 3

Swiss-wide predictive model of urban sprawl at 1ha resolution for three socio-economic scenarios (Trend, A1, A2). Depending on the scenario used urban areas will most likely rise between 3 % and 56 % until 2035. In the most extreme scenario A2 13-15 % of the now existing agricultural areas in Switzerland will be overbuilt. Only in Scenario A1 urban sprawl remains fairly stable due to the fact that almost no new urban areas will be overbuilt. Almost all areas of additional sprawl will occur on soils most suitable for agriculture