Some of my work was referenced on the front page of the Waikato Times earlier this week:
Towns between Hamilton and Auckland are crying out for more land and houses for the decades ahead, as population is set to rapidly climb.
Waikato District, between Hamilton and Auckland, will need nearly 9,000 new houses by 2031, as up to 19,000 more people are projected to move there.
Pōkeno has already transformed from a sleepy settlement to a sprawling town, while Ngāruawāhia, north of Hamilton, is in demand for its new housing developments...
Waikato University associate professor of economics Michael Cameron told Stuff there had been “rapid” growth in Waikato District in the last 10 years, which he expects to continue.
In the last decade, the population grew by 27 per cent, or 18,647 people.
“In relative terms, Waikato has been one of the districts experiencing the fastest population growth in New Zealand.
“We’ve projected growth faster than Statistics NZ, and the growth has even overtaken our own projections,” Cameron said.
Most of that growth has been from Aucklanders spilling over the Bombay Hills into Pōkeno, and Cameron tipped that town to keep growing faster.
“There’s a lot of emphasis on central Auckland, but a lot of growth and industry is happening in the South.
“You can see it when you drive along the motorway. Drury is growing, Pukekohe is growing and Pōkeno is growing.”
Waikato District is in a bit of a sweet spot, strategically located between two fast-growing cities (Auckland and Hamilton), and not far from one of the fastest growing areas in the country (the western Bay of Plenty). It isn't much of a stretch to project high future growth for Waikato District.
The main challenges occur when trying to project where in the district that growth will occur. Most territorial authorities in New Zealand are either centred on a single main settlement (e.g. Rotorua, or Taupo), or have a couple of large towns (e.g. Cambridge and Te Awamutu, in Waipa District). Waikato District has several mid-sized towns (Ngaruawahia, Huntly, Pokeno, Raglan), and a bunch of smaller settlements that are also likely to attract population growth (e.g. Tuakau, Taupiri, and Te Kauwhata). So, there are lots of options as to where a growing future population might be located.
That makes small-area population projections that are used by planners (such as those that I have produced for Waikato District Council) somewhat endogenous. If the projections say that Pokeno is going to grow, the council zones additional land for residential growth in Pokeno, and developers develop that land into housing, and voila!, Pokeno grows. The same would be true of any of the other settlements, and this is a point that Bill Cochrane and I made in this 2017 article published in the Australasian Journal of Regional Studies (ungated earlier version here).
The way we solved the challenge is to outsource some of the endogeneity, by using a land use change model to statistically downscale the district-level population to small areas (that's what that 2017 article describes). However, that doesn't completely solve the problem of endogeneity, because the land use model includes assumptions about the timing of zoning changes and the availability of land for future residential growth - if those assumptions put that land use change in other locations, or changed the order of the opening up of zoned land, the population growth would follow.
It is possible to develop more complicated models that incorporate both supply and demand of housing in order to project the location of future growth. However, from what I have seen of these approaches, the added complexity does not improve the quality of the projection (however, it might improve the believability of those projections). For now, models based on land use change are about as good as we can get.
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