Developing integrated models by coupling together existing models; land use, economics, demographics and transport in Wellington, New Zealand

Abstract Economics, demographics, land use change, and transport interact in complex and dynamic ways. To inform urban policy decision-making it is important to develop tools that incorporate the interactions of these systems in meaningful ways. Historically, models of these systems have been developed in isolation, and many agencies have already invested large amounts of time and money into developing these independent models. It is thus often desirable to couple existing models, rather than to develop a completely new integrated model. Coupling together independently developed models introduces many challenges including dealing with different spatial and temporal scales, base datasets and levels of aggregation, as well as bringing up deeper questions around the underlying paradigms, assumptions and limitations of the models. This paper describes the key challenges encountered when coupling an existing integrated model of land use change, economic activity, and population (the ‘Integrated Scenario Explorer’ model) with an existing transport model (the ‘Wellington Transport Strategy Model’) for the Wellington region in New Zealand. The case study results show that the coupling produces substantial differences in the urban land use change looking forward to 2041, specifically it affects the location of the urban intensification. The paper summarises the important considerations for modellers when coupling independently developed models, highlights the importance of understanding the underlying theories of the component models, and emphasises the need to develop pragmatic solutions that are guided by the intended use of the resulting integrated model.