With the benefit of apps which show the weather pattern for the whole of the West Pacific it is possible to get a good overview of the what caused the flooding on the West coast of the South Island.
The warm, moisture laden weather originated near the equator and came in a stream down to New Zealand. We have had many tropical storms or cyclones come down from that region and we have been very lucky that most of them miss us but, of course this last event hit Nelson and had devastating results.
Using the website https://earth.nullschool.net/ it is possible to see the satellite information for the whole world in real-time and get an overview of what is happening.
This last storm came down in a narrow line and missed Northland and Auckland by about four hundred kilometres but what if it had hit Auckland which has a population of 1.3 million people?
A quick look at Auckland Councils flood mapping https://geomapspublic.aucklandcouncil.govt.nz/viewer/index.html which is similar to our FNDC flood maps shows that there is an alarming amount of infrastructure, South of the bridge that is susceptible to flooding including Auckland airport, motorways and housing. Spending a bit of time looking at the flood maps with overlays that include flood prone areas, flood plains and overland flow paths I would suggest that thousands of houses will be flooded and this is not sea level rise, which is pretty bad, but rainfall.
The reason Auckland is so important to us is that it is one third of our economy and if it is incapacitated, we all suffer economically.
Damaging floods vary considerably from area to area so that Nelson has devastating floods with 271nn while Kerikeri had 209mm with minimal damage in the same period. This is because Kerikeri is accustomed to heavier rain storms, it is hilly and drains quickly and a major factor in flooding is the rate at which the rain falls.
My website http://climateoutcome.kiwi.nz/ explains how the rate at which rainfall causes floods but if Kerikeri floods at a rate of 25mm and hour I suspect that Auckland would flood at only 15mm an hour because it is so flat and there is nowhere for the water to drain away quickly.
The main point is that we can’t rely on what has happened in the past to predict the future but must build and protect for what is likely to come and, as we are finding, it is becoming very urgent and very expensive if we do nothing.
In the upcoming Mayoral elections, the contenders are talking about making millions from developing the waterfront but nobody is looking at the risks the city is facing.
k here to edit.