What’s the difference between Hurricane Katrina and Cyclone Gabrielle? The answer is: wind speed and air pressure. But apart from that, what happened in Hawkes Bay in those deluges around the time of Gabrielle is a carbon copy, already for-shadowed, by what Cyclone Debbie did to Edgecumbe in 2017.
I visited New Orleans 13 years after Katrina and many low-lying parts of the city were still ghettos. The Mississippi is the river that passes through New Orleans, and its stop bank systems have enabled huge areas of flat land to be developed for agriculture and to house those on low incomes. While I was there you could stand on the stop banks and easily see that the river level was above developed ground level when the tide was in. A bit like Amsterdam and its dyke system.
Stop banks are designed to keep the river in its bed, and prevent flooding. While Hurricane Katrina was stronger than Cyclone Gabrielle, most damage was caused by the same combination of high rainfall upstream swelling the Mississippi (and Hawkes Bay rivers) flowing to the coast, and the storm surge pushing upstream from the coast due to very strong onshore winds and the low-pressure weather sucking up the sea level. The net effect being river levels rise sharply, which is not a problem if the stop banks have been engineered to cope.
While there are specifics that differentiate the 2023 Hawkes Bay floods from others - such as the amount of industrial forest detritus that got washed down and caused blockages - the large amounts of silt and the high water levels are what happens with unusually high rainfall intensities. Which are increasingly common in NZ as the Tasman Sea warms and cyclones move further south.
The majority of the loss of lives in Hurricane Katrina was due to flooding caused by fatal engineering flaws in the flood protection system, called the levee, around the city of New Orleans. 80% of the city was flooded for weeks. The flooding also destroyed most of New Orleans's transportation and communication facilities, leaving tens of thousands of people who did not evacuate the city prior to landfall with little access to food, shelter, and other basic necessities.
Like Cyclone Gabrielle, Cyclone Debbie formed over the Coral Sea, but instead of tracking to New Zealand, tracked to Queensland first. The storm caused A$3.5 billion in damage and fourteen deaths across Australia, primarily as a result of extreme flooding. This made Debbie the deadliest cyclone to hit Australia since Fifi in 1991. While Debbie lost energy in Australia, it headed back out to sea, building some energy and gathering water from the warm Tasman Sea, tracked to New Zealand, and made landfall.
It tracked from Taranaki, through Waikato to Bay of Plenty. Following heavy rain from Cyclone Debbie remnants, the stopbank protecting Edgecumbe from the Rangitaiki River breached on the morning of 6 April 2017. The town was rapidly flooded, giving residents barely minutes to escape from their homes. Insurance claims totalled more than $90 million.
The Federal Emergency Management Agency (FEMA) is an agency of the USA whose primary purpose is to coordinate the response to a disaster that has occurred in the United States and that overwhelms the resources of local and state authorities. It has been in existence for almost 200 years and arose in response to fire and flooding primarily. Its role in New Orleans during and after Katrina was widely criticised leading to significant changes.
New Zealand’s equivalent is the Earthquake Commission – or EQC – which as far as I am aware has no involvement in the coordination of responses to cyclones and flooding.
I think New Zealand authorities need to recognise the increasing occurrence of damaging cyclones, their randomness, their unpredictable tracks, and their devastating impacts when and where they hit land, and change New Zealand’s national, regional and local planning and flood protection infrastructure systems appropriately.
Highly funded post disaster recovery systems may be necessary, but they are no longer sufficient.
