As man’s ingratitude

RNZ has a report on the purported costs of weather warnings for (ex-)Cyclone Vaianu a few weeks ago.

Northland spending was down 48 percent. Auckland’s was down 46.5 percent, Waikato was down 52.58 percent, Bay of Plenty down 68.32 percent, Gisborne down 51.6 percent and Hawke’s Bay was down 56.34 percent.

That’s at least two more decimal places than I would want to use, but let’s assume the numbers are correct.  There are still a few issues with the attribution to weather warnings.

First, we can’t easily distinguish the effects of the warnings, the effects of the forecast, and the effects of the storm.  Presumably no-one is suggesting that weather forecasts should be edited to make approaching storms look less scary, but some of the reduction in spending would have been a response to the heavy rain and strong winds in the forecast, regardless of a specific warning.  Even if the forecasts were sanitised, people who remember, say, the Auckland Anniversary Weekend storm or Cyclone Gabrielle might want to be cautious about the risks of an approaching storm.  The report says the reductions in spending were highest in the areas where the forecast storm was most intense, but that’s what you’d expect if people were reacting to the forecast rather than to the North-Island-wide warning.

Second, there’s an economic issue that should be clear already to people in or near local government, because it’s part of how convention centres, stadiums, and major cultural events are oversold.  It’s much easier to get people to change where and when they spend money than to change how much money they spend.  Suppose you were planning a barbeque for your kid’s birthday on April 12th. You might well have cancelled it because of the storm warning, but that wouldn’t mean your kid didn’t get a birthday this year. You’d have the event some other time.  Similarly, if you wanted to see a movie (Project Hail Mary seems popular) or you needed to buy a new vacuum cleaner or you wanted to see the fireworks and racing at Waikaraka Park you might well not go out that day, but you might well go some other day when you could easily get to the cinema or Briscoes or when the racing and fireworks were rescheduled¹.  The reduction in spending on the day of the storm is a substantial overestimate of the impact of the storm on spending. (In the same way, stadiums collect money, but a lot of it is money that people would otherwise still have spent in the city).

And finally, there’s an important issue about uncertain predictions.  The storm didn’t in fact cause major damage across the North Island, but that doesn’t mean the warning was wrong.  If you play Russian roulette and survive, that doesn’t mean it was a good bet and you should do it again, it just means you got lucky.  The report gives no reason whatsoever to assume that less caution was warranted for this storm than for the two big storms in 2023 (one of which was seriously underpredicted).  It’s not inconceivable that our weather warnings are poorly calibrated, but any decision of this sort should be based on some actual evidence that they are.

1. Last night. Ask me how I know.