Another month, another flood
AGAIN the heavens opened and the rain came thundering down.
Hundreds of New Zealanders are out of their homes this weekend following evacuations over the past few days. Houses and properties lie damaged by slips, rockfalls and fallen trees; roads, bridges, freshwater pipes and other essential infrastructure have been wrecked by raging rivers; and communities have been torn apart.
Our national catalogue of disasters continues to grow at alarming pace. This time it was Nelson and the Tasman region’s turn to be hardest hit, with destruction in places where it has not been seen for decades.
The Nelson City Council declared a state of emergency on Thursday, with Mayor Rachel Reese warning that the widespread effects of the rainstorm will take not just months but years to fix.
Yesterday, residents of the top of the South Island got some relief from the rain. Instead parts of the North Island, including Northland, Taranaki and Wellington, had to cope with the deluge and further slips and flooding.
While Nelson and Tasman folk have had an awful few days, with 200mm or more of rain falling in some spots, people not far away across the ranges in Buller are breathing sighs of relief that, perhaps, with about half that amount, they missed the worst of it.
Westport remains in recovery mode from the recordbreaking floods of July last year and more flooding in February. Some of the homes damaged then are still being fixed or waiting for work to be started.
Mopping up after yet another flood event would have been the last thing anyone there wanted to do.
The “atmospheric river” of tropical air responsible for this week’s heavy rain was wellsignalled by meteorologists this time last week. MetService warned it was going to cause flooding and significant damage, and Niwa, not the Government’s official forecaster for severe weather, chipped in with its own views of where the worst weather would be.
You didn’t need a weatherman to know which way the wind was blowing (with apologies to Bob Dylan) on this occasion.
It was clearly going to be an exceptional event across several days which would affect a great many people.
We rely on MetService forecasters’ experience and expertise, and the fearsome power of computer modelling, to pinpoint the nuances of broadscale severe weather, to allow residents and local councils and emergency managers to make the best decisions in the hours ahead.
Yet were the people of Buller and of NelsonTasman wellserved by the official warnings this time? There is no doubt there was plenty of notice that stormy, hazardous weather was on the way for parts of the upper South Island. But there is a feeling that perhaps MetService failed to nail the likely outcome as well as it could have.
Weather forecasting is a highly specialised science, and making decisions which affect thousands of people is extremely difficult.
If MetService is considering issuing a rare toplevel “red warning”, reserved for the most extreme weather which requires an immediate response to save lives and livelihoods, it does so in consultation with regional council hydrologists.
On this occasion, it seems its original red warning for Buller overpredicted the amount of rain that would fall and could have been left as a regular orange warning.
However, the reverse is the case for Nelson. MetService upgraded its heavy rain warning from orange to red on Wednesday afternoon, by which time the Maitai River flowing through the centre of the city had already burst its banks.
Forecasters of course cannot also be expected to be experts in hydrology, and this is where the input from council hydrologists is crucial to the success of the red warning system.
Nobody is going to complain if they don’t get as much flooding rain as was predicted, but it is still vital the forecasts are as spot on as they can possibly be.