"In about 1900 the four places were not that much different, but there has been this divergence and Auckland has become way above the rest," he said.
By 2031, Wellington is projected to have 499,300 people, Christchurch 538,200 and Dunedin 134,700, a total of 1.17 million or about 59 per cent of Auckland's projected tally. The new projections are based on slightly higher birthrates, longer life expectancy and higher net immigration over most of the next 20 years than in the last update in February 2010.
The migration numbers are the least predictable. The projections incorporate a much lower net inflow than previously expected between 2007 and 2016, but assume a net inflow of 12,000 a year from 2016 onwards, up from 10,000 a year in the previous projections.
Statistics NZ demographer Kim Dunstan said this was based on the long-term average net inflow of 11,690 a year over the 22 years to June.
"There is uncertainty about it but we know our immigration goes up and down," he said. "It would be tempting in a period when there is a net outflow to say this is a new average, but as demographers it's important to take a longer-term perspective."
The upward revision has lifted expected 2031 populations for all regions except Canterbury, which was hit by earthquakes, and Bay of Plenty and Wellington, where growth rates in the "retirement belts" of Tauranga and the Kapiti Coast have been revised downwards.
Dr Douglas Fairgray, of Auckland-based Market Economics, said finance company collapses in the recent recession had wiped out the savings of many elderly people, which might be forcing more of them to keep working and stay where they were. However, the Bay of Plenty and Canterbury are still projected to post the second-highest average growth rates over the whole period from the last Census in 2006 to 2031.
Canterbury's population of 560,800 in June last year was 11,000 less than projected before the earthquakes. But it is expected to recover to 580,600 by 2016 and grow to 649,200 by 2031, posting growth rates faster than the pre-quake projections but still below the national average.
Victoria University geographer Philip Morrison said Auckland's growing dominance was good for the national economy.
"There is growing evidence that agglomeration increases labour productivity, including chances of employment and expected incomes," he said. "The larger Auckland gets, the greater the economies of scale and the possibility of greater economic returns. What we have to be careful of ... is that the advantages of increasing size do not get negated by reductions in quality of life."
