Those of you who are not particularly aware of the way electorate boundaries are drawn may not be aware that New Zealand actually has a quota for South Island electorates. Basically, regardless of the relative population imbalance, the South Island is always guaranteed to have at least 16 electorate seats. Essentially how they work is that the median electorate size is set to 1/16th the population of the South Island at the time electorates are reviewed, then the North Island seats are divided up relative to this so that they don’t vary by more than 5% from the median size. After that, Māori electorates are “superimposed” over the borders of the general seats in a way that divides them roughly by the Māori electoral roll population, and so that there’s a proper proportion of Māori seats to General seats.
Unless there’s a sudden exodus of North Islanders to the South Island at some point, or a mass immigration to the South Island to get away from Donald Trump, there’s likely to be a long-term issue with that. Why? Because of something I call “list seat parity,” which is the idea that parties with significant shares of the Party Vote, like National, Labour, the Greens, and New Zealand First, should never have overhang seats.
MMP is intended to have a healthy proportion of list MPs- the original ratio was that just above 41% of MPs would be list MPs, presumably with the intention that the ratio would stay around 5 list MPs to every 7 electorate ones. We have added two new electorates to the North Island since we switched to an MMP system, reducing the number of list MPs to 49, assuming no Independents are elected. (independents elected at a general election remove a list seat vacancy rather than creating an overhang so that Parliament doesn’t inflate grossly due to independents being elected, a rule which hasn’t become relevant since like, ever, as every “independent” in our system has either been someone who quit their party, or a lone MP optimistically having their own political party, presumably on the theory that they’ll earn a second seat again sometime in the future. Not happening, Seymour and Dunne, not happening.)
It theory, there’s really nothing wrong with actually having less electorates than we do, but 60%-ish of MPs being electorate MPs isn’t unreasonable and doesn’t hasn’t threatened parliaments much larger than about 125 MPs in the past.
With 70 seats, there’s a reasonable expectation of list seat parity, but it’s not guaranteed. Almost all electorate seats are won by National or Labour. There are only five others likely to be in serious contention in the current political climate, (which as we know, can rapidly change, but this list is actually somewhat on the high side by historical standards) and those are Epsom, Northland, Ōhārui, Waiariki, and possibly Te Tai Tokerau. (As nobody polls for electorates, we have no real clue whether the Māori party agreeing not to stand there will matter enough to unseat Kelvin Davis in 2017. I’m assuming it’s within the realm of possibility until I have good reason to think otherwise) Let’s assume that small parties won’t take more than five electorate seats. That currently leaves 66 currently for Labour and National. Labour, with roughly 27.5% of the party vote, earned 27 seats in 2014.
That’s not currently a problem, but with some small changes to the way our elections work, and a small boost in North Island population, (ie. a few more electorates) it might be.
Imagine for a moment that the Greens start eating into Labour’s party vote but not their electorate vote. Let’s assume in this calculation Labour can hold on to a similar number of electorate MPs- it only takes about a 5% shift to the Green party for Labour to start getting overhang MPs, compared to current polling, and that’s without any extra North Island electorates, and assuming Hone takes back Te Tai Tokerau. A roughly 4% shift to the Greens from Labour will start giving them overhang seats if the 2020 election adds a new electorate seat again. (note the link shows all of Labour’s seats as electorate seats with no overhang, that’s because the Commission’s calculator doesn’t allow for us to award more than the current 71 electorates. I take it you’re capable of using your imagination)
I would much prefer that instead of having a South Island quota, we simply set the number of electorates to 70 in legislation, and the South Island get its share based on how many 70ths of the population live on the South Island and are part of the General Roll. This will limit the chance that either Labour or National (but most likely, Labour) will end up with overhang seats in the future. This should limit the likelihood of overhang seats for Labour in the future, especially as we’re approaching the point where certain Wellington electorates like Wellington Central might actually spontaneously decide to elect a Green candidate even though they’re not campaigning for the electorate vote. (In terms the party vote, most Wellington electorates are three-way races between the Greens, Labour, and National)
If we don’t adjust the South Island Quota, however, we’re in for an interesting problem in the long term. Until relatively recently, about .5% more of the population would live in the North Island every census, but that rate’s actually increased a little bit recently. Assuming that trend continues, it won’t take too long for us to end up with nearly 90 electorates, (it only takes a population growth of just over 1 million in the North Island, if you assume the South Island population stays static) which would make breaking list parity the rule, rather than the exception. (in fact, it was actually one of the potential “reforms” to MMP that Labour had been talking about at the time of the MMP review was to add another 20 or so electorates, because they knew that the party most likely to get overhang seats that way would be Labour) This could actually happen in 20-30 years time, depending on migration numbers, so I hope I’m not the only one noticing that the South Island Quota is a terrible way to determine how many electorate seats we have.