Land-use scenarios for assessing climate risk as a tool for spatial planning: a case study of the Stuttgart Region, Germany

Spatial development, particularly the rapid expansion of urban areas, is increasing disaster risk in city-regions around the world. The planning region of Stuttgart is a growing polycentric region with a high demand for housing and commercial space, and at the same time faced with increasing risk of pluvial flooding and heatwaves. Spatial planning that controls and coordinates urban development is an important tool for ex-ante disaster risk reduction. However, planners face a complex task to weigh up a myriad of development goals of which risk reduction is just one. Decision-making tools for planning practitioners and the public that quantify resilience factors spatially can support the integration of resilience and risk considerations into planning processes. In our research, we investigate the use of land-use scenarios as a way to measure the relevance of land to the hazards of pluvial flooding and the urban heat island effect and thus to risk reduction. We do so with a particular focus on operationalizing such a quantitative assessment for the regional planning level, whose task it is to coordinate the spatial development of the municipalities. Such coordination is particularly important in the context of disaster resilience in urban regions such as Stuttgart, because, for example, the development of land in one municipality can increase water runoff or decrease cooling airflows in a neighboring municipality.

In our contribution to this session, we share our insights from a combined effort by research, modelling and planning practitioners to operationalize land-use scenarios as a way to quantify the effect of urban development on risk. A central aim of our approach was relevance to regional and local planning processes. The land that we considered as potential for urban development was thus based on the current planning law. We constructed two land-use scenarios, in which all land in the region with potential for development was fictitiously used for building housing but in two different ways – one with a building density and height and level of soil sealing typical to the local setting, and the second with a more compact urban form with more green and less impervious surfaces. The aim was, firstly, to measure the effect of urban expansion on hazard exposure and, secondly, to determine if through a compact and climate-sensitive urban form the needs for more housing could be met without increasing hazard exposure. The pluvial flood hazard model and an urban climate model of the two scenarios provided useful results for the first aim, but less so for the second. In our contribution, we will share the methodological challenges of translating the scenarios for two different types of models, and discuss the results and their potential as a tool for use in spatial planning processes.