DOT helped the Nelson and Tasman councils in New Zealand develop customised population projections to understand how the population of the area would change over the next 40 years. They were particularly interested in understanding population impacts on infrastructure, housing, public services, and community development. The councils needed a bespoke solution that incorporated different potential scenarios.

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DOT developed a customised population projection by working with the councils to understand local factors influencing birth and death rates, migration patterns, and housing trends in their region. Through this collaboration, assumptions about fertility, mortality, migration, and household size were collectively informed by local demographic contexts, past patterns of population change, and wider demographic trends. This generated a set of bespoke model assumptions relevant to each council.

Using the Cohort Component Method, DOT developed a model to project the area’s population by age and sex over the next 40 years as well as counts of dwellings and households. We developed models for each territorial authority (TA) area as a whole and for each neighbourhood (Statistical Area 2) within the TAs. The model generated three different scenarios (High, Medium and Low growth), by taking into account variations in birth and death rates and changes in migration patterns. The model variants are informed by historical variation and anticipated future changes in fertility, mortality and migration trends.

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DOT provided the councils with a comprehensive report and data files of how the area’s population was likely to change over time, focussing on changes in age structure and patterns of population growth. Population ageing was identified as a dominant process, with over 25% of the population projected to be aged over 65 years by the late 2050s. DOT also demonstrated the role of migration in sustaining the number of births and slowing the progress of population ageing in their region. This highlighted the importance of sustaining both the level and age-profile of recent migration if they wished to sustain population growth into the middle of the century. The projections provided the councils with insights that informed long-term plans and resourcing for infrastructure, public services, and community development. 

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