Why doesn’t the tool work on a mobile device?

Due to the size and complexity of the data, this tool works best on a laptop or desktop computer. Our apologies, but we are unable to optimise the maps for mobile with the technology available.

Why doesn’t the key show both sea-level rise and vertical land movement?

Each dot on the map represents a measurement of vertical land movement. Dark red represents uplift with a gradient to dark blue representing subsidence. What you are seeing doesn't take into account sea level rise projections, as there’s only about a 10% difference in regional sea-level rise between Northland and Southland. It is vertical land movement that really makes the difference between locations near to each other. Click on the dot to see the combined effect of regional sea-level rise and vertical land movement.

What do the graphs show?

The graph automatically displays the shared socio-economic pathway the world is trending towards at the moment. This is the way the IPCC (Intergovernmental Panel on Climate Change) looks at projected climate change.

The bottom line shows the sea-level rise projection without vertical land movement, the upper line shows it with vertical land movement. You can turn off the projections that do not include vertical land movement and just see the sea-level information. This makes it very clear the difference vertical land movement makes.

You can also play around with the time period displayed on the y axis and the sea-level measurements on the x axis to get a closer look. You can also check out different pathways. We like to add the high emissions scenario and the low emissions scenario to see the range of possible sea-level rise for this location.

Why aren’t there projections for Waiheke, Aotea/Great Barrier, and Rēkohu / Chatham Islands?

Unfortunately, we do not yet have the data for these islands. We acknowledge this is not ideal and will work to provide outputs for all of the coastlines of Aotearoa in our next research iteration. This will include the areas we could not cover in our recent study.

With Waiheke Island, we suspect the projections will be similar to nearby vertical land movement estimates for Auckland (~1 to 2mm a year) which will accelerate sea-level rise by a decade or so. With Aotea/ Great Barrier Island, we suspect the vertical land movement will be relatively low and/or similar to nearby vertical land movement estimates for the top of the Coromandel Peninsula. However, we cannot confirm these conjectures for sure until the analysis has been done.

Because Rēkohu / Chatham Islands are so far away from the mainland we do not have any way to predict vertical land movement. We hope to include these motu in our next round of research.

Why aren’t there projections for lakes and rivers and areas further inland?

The data we had was only available for the coastline of Aotearoa New Zealand, and does not continue up many tidal rivers (e.g. to Dargeville). We are currently working on obtaining a license for an interferometric analyses (InSAR) data set that covers much more of the country.

The Kaikoura coastline rose significantly during the 2016 earthquake sequence, yet the SeaRise map indicates sinking. How can that be?

Our vertical land movement estimates are based on a time series (2003 to 2011) that pre-date the Kaikoura earthquake. However, we have also looked at a longer time series to check how reliable these ‘inter-seismic’ between-earthquake estimates are. The data show that the subsidence we observed before the Kaikoura earthquake resumed within a year after the earthquake (in fact subsidence/sinking rates are much higher). So, while the land generally went up fast during the earthquake, it has since resumed subsiding. The earthqauke reset the coastline datum (instantaneously), but the pattern of long term subsidence continues.

These variations highlight the challenge we face living on a dynamic surface. Overall, however, we are confident that our estimates of the rate and direction of subsidence/uplift are reasonable and appropriate for projections over decadal time scales, as the Earthquake cycle for any particular point on the NZ coastline is about 100 years.

How accurate is the data?

Our vertical land movement estimates have errors associated with them and are included in the error envelope in the sea-level projections.

For example, our data shows where the land is sinking in the Bay of Plenty, which includes areas like Tōrere as well as Matatā and Katikati. Looking at one point of coastline at Matatā, where the land is shown to be sinking by 2.86mm a year, it is projected that in a world with moderate emissions sea level would have risen by almost 20cm from 2005 by 2030.

However, saying that “land is sinking at 2.86mm a year” overstates the certainty – this is a median estimate with error. We actually estimate that the land is sinking at that Matata site by 2.8 +/- 1.5mm a year. So the error is pretty large here. It might be better to say between ~2 and ~3mm a year to emphasise that a single number is unlikely. Unfortunately, this kind of uncertainty is hard to show on a map.

The same is true for our sea-level projections. The sea level at Matatā is likely to reach a height 20cm above where it was in 2005, anywhere between 2025 and 2040 (this is the likely range and accommodates uncertainty in climate drivers and our estimates of vertical land movement). The median is near 2030.

How does this fit in with what the IPCC (Intergovernmental Panel on Climate Change) is saying?

There is a range of sea-level rise estimates by 2100. Depending on greenhouse gas cuts and reinforcing climate feedback loops, marine ice sheet, and ice-face instability we could have 0.5m to 2m of sea-level rise by 2100.

We have included the IPCC AR6 low confidence projections in our work, which specifically include the DeConto and Pollard Antarctic Ice Sheet model and expert judgment projections that include ice sheet instabilities that can cause rapid and large increases in sea level.

For example, these low-confidence, high-impact projections indicate that sea-level rise at Wellington under SSP5-8.5 will be as much as 2.11m by 2100 if you consider the upper bound of the likely range.

What does this mean for other countries?

The bottom line is that our new estimates of local vertical land movement when added to the latest (IPCC AR6) regional estimates of sea-level change driven by global factors (e.g. ice sheet melt, thermal expansion of the ocean, glacier melt, land water storage) increase the rate and magnitude of local sea-level rise in many locations around the coastline of Aotearoa New Zealand. So sea-level rise is faster than the global mean at many locations around Aotearoa New Zealand due to rapid sinking along much of our coastal margin.

The local vertical land movement effect occurs around the world. Anywhere sedimentary basins are sinking or tectonic subsidence is significant will accelerate sea level rise (and vice versa). Until now, estimates of local vertical land movement at relatively high resolution have been limited. Satellite Aperture Radar (SAR) data and interferometric analyses (InSAR) have helped us fill this gap.

What are the next steps for the programme?

If we receive funding, we aim to take into account earthquake risk and improve the resolution of the tool to a scale that encompasses individual buildings. We also want to work on our community engagement and encourage the government to fund a coastal adaptation platform.