Ongoing impact of Canterbury earthquakes reflected in the latest subnational population estimates

This week Statistics New Zealand released subnational population estimates for the year to 30th June 2012. These releases provide estimates of the population at the regional and territorial authority (TA) level. The subnational population estimates are published annually whereas the national population estimates (ERPs) are published quarterly.

The provisional population estimate for New Zealand for the year ending 30 June 2012 is 4,433,100 – an increase of 27,900 or 0.6% from the previous year. The key facts and points of interest from this release will be explored in two blog articles. Firstly, we will look at Christchurch and the Canterbury region.

Population decline in Christchurch

Both the media and public were most interested in seeing how Christchurch and the Canterbury region have changed in the twenty months since the February 2011 earthquake. The Christchurch city TA decreased in population to June 2012 though there was a greater population loss in the period directly after the first large Canterbury earthquake, which was reflected in the 2010-11 ERP. This year’s estimated population decrease of 4,600 is a further loss of 1.2% of Christchurch city’s population. The components of this figure (see table below) are a net migration loss of 6,000 and a positive offset of 1,400 people by natural increase (births-minus-deaths).

Population change of territorial authorities in the Canterbury region by component (Year ended 30 June 2012)

Growth in other parts of Canterbury

On the other hand, while the Christchurch city TA had very large declines when compared to the rest of New Zealand, the territorial authorities immediately surrounding Christchurch showed increases. Five Canterbury TAs grew at a rate higher than the national 0.6%. These were Selwyn, Hurunui, Ashburton, Waimakariri and Mackenzie.

Population change of territorial authorities in Canterbury (June 2011-2012)

Source: Statistics New Zealand

The Selwyn, Hurunui and Ashburton TAs were the fastest growing territorial authorities in New Zealand for the June 2012 year. This pattern in Canterbury is credited to people leaving Christchurch city and relocating in surrounding towns, whether just for the immediate future or as part of a long term plan. Analysis of the “address five years ago” question in the 2013 Census of Population and Housing will be particularly useful in revealing the internal migration patterns of Cantabrians.

Share of population growth in Canterbury (Year ended June 2012)

Source: Statistics New Zealand

Changes in Christchurch’s demographic profile

Over the June 2010-2012 period, Christchurch city experienced significant decreases of young people, families and children (who follow families/guardians) although there were some increases in population for the 20-24 age group which could be representative of incoming students to the city’s University and other tertiary institutions. There was also an increase in males aged 25-29, most likely related to tradesmen and other reconstruction workers who have relocated to Christchurch from around New Zealand for reconstruction work opportunities. For the same age group, females experienced a decline of over 1,000. There is a visible change from decline to growth in the 50-74 age groups and the 85+ age group in Christchurch which would suggest natural ageing into these age groups from younger ones but also the lower likelihood that these people would leave Christchurch and relocate elsewhere at that age. See this for more detail.

In the previous release, population estimates showed that Christchurch city experienced a 1.9 times greater population loss of 8,900 people (2.4%). Without the natural increase offset the net migration loss for that period was 10,600 – a net migration loss of 16,600 people for the two year period. Soon after the February 2011 earthquake, I wrote a blog in which I referred to an ANZ economics and market research newsletter which estimated that 15,000 people may leave Christchurch for good. Whether the 16,600 who left the city will be gone for good is unknown but that original estimate is very close.

Looking forward to the 2013 Census…

Like many of our local government clients, we are eagerly looking forward to the results of the 2013 Census of Population and Housing in New Zealand. As well as the rich information about communities and the nation, the Census data is used to prepare base ERP population, which subsequent year’s estimates are based on. It is well known that data quality of ERP decreases the further out from the base year that we are. We can expect to see some revisions of subnational estimates as part of the usual rebasing process. The ERP of geographic areas in Canterbury are likely to change doe to the high level of population movements recently.

Next, we’ll look at some other key points that have come from this latest release of subnational population estimates for New Zealand.

A special thanks to my colleague Esther for assisting with this blog and the upcoming one.

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