Prof Tim Naish is one of New Zealand’s foremost climate scientists. He and Richard Levy of GNS Science co-lead a $7 million research program called NZSeaRise. They visited Thames recently to assess sea level rise projections for the township. Prof Naish confirmed that when land subsidence on the foreshore is added, parts of Thames have a very high local sea level rise rate of 14mm per year. The NZSeaRise research will, therefore, focus on Thames (and the Hauraki Plains) because of the acute risks these areas face from rising seas.
Prof Naish sent this tweet after his visit to Thames confirming that the relative or local sea level rise rate for parts of the Thames foreshore is around 14 mm a year. This is made up of approximately 8- 10 mm of land subsidence a year. These are some of the highest rates of subsidence in New Zealand as measured by survey, GPS and InSar (satellite). The other component is sea level rise of around 4mm per year.
Do the maths – 1 decade at 14mm = 0.14 m, 2 decades = 0.28 m, 3 decades = 0.42m. This is without projected future sea level rise.
In this interview in the Otago Daily Times Prof Naish confirmed that around 20 – 30 cm of future sea level rise is built into the system by about 2060, regardless of efforts made to reduce greenhouse gas emissions.
He also points out there are large uncertainties as to how fast the polar ice sheets will melt. Some ice sheet models suggest that the potential contribution of polar ice sheets may have been underestimated by as much as 80 cm in the current IPCC report.
Even with a modest sea level rise added to the very high rate of subsidence on the Thames/Plains foreshore, we are looking down the barrel of half a metre of local sea level rise within just a few decades.
Both Thames and the Hauraki Plains are very similar to Dunedin, (which is another focus of the NZSeaRise study) because sea level rise will likely accelerate groundwater inundation and flooding from overtopping of walls. There is, therefore, the real threat that surface flooding in Thames township due to seawater intrusion into groundwater beneath sea walls and overtopping of sea walls will occur in short order and ever more frequently on high/spring tides. Thames already has “sunny day flooding” in some streets, and scores of houses and businesses were flooded from the sea on Jan 5 2018.
GNS Science has already undertaken a groundwater study of the Hauraki Plains and NZSeaRise have begun discussions with Waikato Regional Council about a groundwater inundation study looking at the influence of future sea-level rise.
NZSeaRise is funded by the Ministry of Business, Innovation & Employment, and involves 35 researchers from Victoria University of Wellington, University of Otago, GNS Science and NIWA.
I have been called a “scaremonger” (and much worse) when in the past few years using official data, I have warned about this combined threat to Thames from land subsidence, sea level rise, and groundwater flooding. Now that this major research project led by our best NZ scientists is going to focus on Thames and the Lower Firth of Thames can we please stop the name-calling, the denial of climate science and start to give these issues the serious attention they deserve.
As Tim Naish says in his tweet — what are the adaptation options for Thames? With an annual 14mm of relative sea level rise already happening in some parts of the Thames foreshore and much more global sea level rise to come, there are some tough decisions to make.
This an emergency. We need to treat it as such. For a start, the Mayor and District Council must stop pretending that they lead the way on climate change when they are dragging the chain. They must end the farce of refusing to say whether humans cause climate change as a smokescreen for outright climate science denial. They need to be honest with the people of Thames about the multiple hazard threats the town faces. And they must urgently commit more resources in tandem with NZSeaRise and the Regional Council into research and adaptation options.