Sinking cities
Much of the Bay of Plenty will have more time to prepare Sea level rise happens Slower Faster -0.5 0 0.5 m than average by 2100 under high emissions (SSP3-7.0) Parts of Christchurch are sinking while others are rising, but the city is overall more vulnerable to sea level rise Stable or rising land will buy much of the Bay of Plenty more time to prepare for higher sea levels Many parts of Auckland's coast are sinking surprisingly rapidly Sea level rise happens Slower Faster -0.5 0 0.5m The Wairarapa coast is sinking rapidly, doubling the effects of sea level rise than average by 2100 under high emissions (SSP3-7.0) Parts of Christchurch are sinking while others are rising. Some popular beaches are slightly more vulnerable to sea level rise because of subsidence Stable or rising land will buy much of the Bay of Plenty more time to prepare for higher sea levels Many parts of Auckland's coast are sinking surprisingly rapidly Sea level rise happens Faster Slower -0.5 0 0.5m than average by 2100 under high emissions (SSP3-7.0) The Wairarapa coast is sinking rapidly, doubling the effects of sea level rise Parts of Christchurch are sinking while others are rising. Some popular beaches are slightly more vulnerable to sea level rise because of subsidence What am I looking at? The unlucky places are in bright pink . You might think the ocean would rise evenly around our coastline. This map shows how far from the truth that is - and how widely different the experience of sea level rise will be for different parts of the coastline. Unlucky places in bright pink could see an extra half a metre by the end of the century. Fortunate spots in shades of gold will experience less sea level rise than the rest of us, thanks to quirks of their geology. Note: this map is based on high (but plausible) greenhouse gas emissions, well above what countries are aiming for under the Paris Agreement. However, the same geographic pattern applies at lower global heating levels, even though the amounts of sea level rise are smaller. ELOISE GIBSON Climate Editor FELIPPE RODRIGUES Data Reporter You might not notice if youre strolling along the harbour, but much of Auckland is sinking. So is much of Wellington, bits of Christchurch, most of the Wairarapa coast and land around Napier airport. In contrast, much of Tauranga is standing still or even rising gradually out of the ocean. The tiny settlement of Pikowai (between Te Puke and Matata in the Bay of Plenty) is rising fast, in geological terms, while Thames is on a veritable roller-coaster ride. In the space of just 2km of shoreline, Thames goes from rising, to sinking, to rising again. None of these movements is big enough to bother the average resident as they go about their daily lives - they amount to just 0-4mm of movement a year. However, new measurements of these movements - released publicly today, for every 2km of New Zealands coastline - drastically change how long many communities have to prepare for coastal floods. Take Lowry Bay, a narrow, rocky swimming beach in Wellingtons Lower Hutt, around the coast from Petone. This gravelly piece of seaside is sinking up to 3.8mm a year, coincidentally about the same amount (3.5mm) that the sea around New Zealand is rising. Add the two together and you get double the global average rate of sea level rise. Surprisingly, small amounts of sea level rise can have devastating impacts: research for former Parliamentary Commissioner for the Environment Jan Wright found just 30 centimetres higher seas would turn a one-in-100 year flood event in Wellington into an annual event for the capital . Thats the kind of extreme flooding that, today, is considered rare - and its big enough to gouge the citys seawalls. You might expect the oceans around Aotearoa would rise evenly, like a filling bath - and indeed, thats what most of our coastal planning assumes will happen. National guidance published by the Ministry for the Environment projected 0.461.05m of sea-level rise by 2100, depending on how quickly people and governments cut carbon emissions. Like most countries, New Zealand has based its planning mainly on global average projections from the Intergovernmental Panel on Climate Change (IPCC). But as glaciers and polar ice sheets melt and sea water expands with heating, it wont affect every bit of coast evenly. Not only do gravity and local factors, such as the slope and shape of harbours, affect how far the flooding goes - it turns out Aotearoas coast is itself sinking and rising, by wildly varying amounts. Flooding on Tamaki Drive in 2015. Photo: Bevan Read/Stuff Flooding on Tamaki Drive in 2015. Photo: Bevan Read/Stuff The new dataset from the NZ Searise project (which includes scientists from GNS Science, Niwa and Victoria University) shows how these movements affect the entire coastline. The project uses Synthetic Aperture Radar Interferometry (InSAR) data; researchers gather and compare radar pings received back from satellites bouncing off Earth. By comparing radar images of the same location, they measured movement of the ground surface toward or away from the satellite. They then checked the accuracy of their findings by comparing them with nearby GPS readings. Its not perfect. The measurements are spaced 2km apart (meaning they miss some local changes) and some places have more accurate estimates than others. The results are median numbers drawn from a comparatively short time record (2003-2011), and they assume future land movements will be similar. But its the first time New Zealands whole, wobbly, shifting coast has been tracked with this kind of coverage and accuracy. And it shows how out-of-sync with reality our one-size-fits-all approach has been. Where the NZ coast is sinking or rising How to read this: North island Sinking Rising NLD AKL east AKL west WKT west WKT east TAR BoP WLG GIS HWB MAR NEL South island TAS CAN WC OTA SOU Where the NZ coast is sinking or rising How to read this: North island South island Rising Sinking MAR NEL TAS NLD AKL east CAN AKL west WC WKT west WKT east OTA TAR BoP WLG SOU GIS HWB Where Aotearoas coast is sinking or rising How to read this: Rising Sinking North island South island MAR NEL TAS NLD CAN AKL east WC AKL west WKT west WKT east OTA TAR BoP WLG SOU GIS HWB Where Aotearoas coast is sinking or rising How to read this: Rising Sinking South island North island MAR NEL TAS NLD CAN AKL east WC AKL west WKT west WKT east OTA TAR BoP WLG SOU GIS HWB What am I looking at? At first glance, these two ring-shaped graphics might not put you in mind of the North and South Islands. Look closer, however, and they reveal how much the land is rising and subsiding in your region - and the huge variation around our coasts. To find your region, look at the ring representing your island (left is North, right is South). Follow the ring down to move south down and around your island. The west coast is on the left, the east coast on the right, just as they would be on a map. Some regions (such as Auckland and Waikato) straddle both coasts, so youll see their west coasts on one side and east coasts on the other. If the jutting lines are shaded pink and pointing towards the middle of the ring, your region is sinking. Youll see that thats the case for most of the North Island, aside from a few lucky points where the lines jut outwards into the grey-shaded area, indicating rising land. Each jutting line represents a point on the coast 2km from the last one, which is why Northland and Southland, with their long coastlines, seem to occupy so much of their circles. The length of each line represents how much the land at that point is sinking or rising each year. You can see that one region has the most dramatic movements (clue: its also where the politicians live). advertisement Based on current international emissions reduction policies, global sea levels are expected to rise about 0.6m by 2100, says Tim Naish, who co-leads the programme. However for large parts of Aotearoa this will double to about 1.2m due to ongoing land subsidence, he says. We have less time to act than we thought. Back to Lowry Bay, which neatly demonstrates the problem. The sinking of the land there means that instead of 15cm sea level rise over the next 30 years, the area is in line to get 30 cm, says Richard Levy, the Searise projects other co-leader. (All projections in the Searise project are against 2005 levels). If you're planning for that 30cm threshold that turns a 100-year [flood] event into an annual event, you might think you'd have until 2070 until that threshold was breached, if we managed to track along on the Paris [Agreement] and get our emissions under control, says Levy. But with vertical land movement, you bring it forward to 2040. So you lose 30 years of time, he says. Waves smashing over the road at Lowry Bay. Photo: Robert Kitchin/Stuff Waves smashing over the road at Lowry Bay. Photo: Robert Kitchin/Stuff Residents plan their lives around these kinds of projections. Whether theyre investing in coastal buildings or renovations, looking to buy seaside property, or wondering whether their new abode will qualify for flood insurance, they could be looking at flooding risk maps made by councils, using average sea level rise. Councils rely on projections too, for planning and maintaining town centres, roads, airports and water pipes and writing development rules. Even small differences matter: An assessment in 2019 found that for every 10 centimetres of sea level rise, thousands of people and billions of dollars worth of houses - plus more roads, pipes and infrastructure - become exposed to potential flooding during extreme events . Land sinks and rises for all kinds of reasons. There might be an old landfill whose compacted rubble is slowly subsiding beneath the surface (as there is in part of Thames). A town might be built on the slowly-compacting sediment of an old river bed. Or land could be rising due to volcanic activity underneath it, as is believed to be happening to Pikowai. One of our biggest cities (Wellington) is on the edge of a tectonic plate that is slowly being pulled under another plate, dragging the lands elevation down, or pulling down on the eastern side of the North Island, as Levy puts it. That same effect makes Wairarapa, up the coast from Wellington, the fastest-sinking area of the country. It is also the area where some of the most reliable measurements have been taken, says Levy. This gives the Wairarapa coast the dubious honour of having the nations quickest rate of effective sea level rise. The Wairarapa Coast near the settlement of Ngawi. Photo: Robert Kitchin/Stuff The Wairarapa Coast near the settlement of Ngawi. Photo: Robert Kitchin/Stuff If Wellington and Wairarapa were to suffer a huge earthquake along the Hikurangi subduction zone, a faultline which lies off the east coast of New Zealand, the consequences would obviously be devastating. But one upside would be that the resulting uplift would probably stop the coastline sinking and allow the ground to spring back up, stalling the impacts of sea level rise. Thats what happened in the Kaikoura earthquake in 2016, when formerly underwater rock ledges suddenly rose out of the ocean . (The effect was temporary. The area is now sinking again). Pikowai in the Bay of Plenty is rising so fast that it could outpace sea level rise if the world cuts emissions quickly enough, says Levy. Under the most optimistic scenario, Pikowai may see a small fall in sea levels. (Under less-cheery scenarios, when emissions rise more, the rate of sea level rise will outstrip the land movement.) The Searise team brought in the latest sea level science, including recent modelling of the Antarctic ice sheets , adding that to a map of the New Zealand coastline made using InSAR. Layered on top of that is the biggest wildcard of all - planet-heating emissions. Stuff looked at two scenarios - a plausible-but-pessimistic one (where countries dont make much effort and various factors conspire against emissions cuts) and a more likely, middle-of-the-road future (where the world acts faster but still misses the goals of the global-warming-fighting Paris Agreement), to show how much emissions matter to sea levels (with or without the coastline moving). You can read more about this in the text box below. Two possible futures. Climate projections are uncertain because no one knows how much climate pollution people will make from now. The IPCC gets around this by modelling a huge range of social and economic futures - population, technology, education, international rivalry, inequality and more - and combining these with heating models to show a range of scenarios. Weve used two scenarios - middling climate pollution, where countries take some climate action but miss their Paris Agreement target of keeping the heat under 2C, and a pessimistic (but happily less likely) scenario, where collective action fails and global heating reaches 3.8-4.2C. In IPCC terms, these paths are known as SSP2-4.5 and SSP3-7.0 . There are many other possible futures, including much better ones, and nobody knows which one will eventuate. Weve used these to show how much difference it will make if governments rein in emissions. The effects of ongoing climate pollution get particularly noticeable after 2050. Until 2050, our coast will largely experience the effects of what weve already done - pollution weve already created. Sea level rise takes a while to unfold, so the heating already caused by our gases is still working its way through the ocean system. After 2050, though, the paths diverge, depending on emissions. At Lowry Bay, for example, by 2100, the difference from middling to higher emissions adds up to about 20cm - enough to make an impact on those people and assets that would be safe under one future, but not the other. 20 centimetres matters. If we can get on top of climate change, by 2100, we've saved ourselves 20 centimetres, says Levy. The country is on a pick-a-path adventure, where nobody quite knows what they are planning for - only that they may need to plan for it sooner than they previously thought. How do we adapt to a future where sea level is rising, but our land is also constantly evolving. It's tricky, says Levy. We want to build permanent structures on the coast and we expect the land to stop moving and shifting when we've done that. And it's just a bit crazy trying to control and constrain nature. advertisement Tamaki Drive Tamaki Drive sinking profile 0 -3mm per year Cliff Rd Pakanoa point 0.4mm Sinking at 2.7mm per year Tamaki Drive Pakanoa point Port Cliff Road Tamaki Drive sinking profile 0 Auckland port 2.4mm -3mm per year Cliff Road Pakanoa point 0.4mm Subsidizing at 2.7mm per year Tamaki Drive sinking profile 0 Tamaki Drive Pakanoa point Auckland port Port Cliff Road 2.4mm Cliff Road 0.4mm -3mm per year Pakanoa point Sinking at 2.7mm per year Tamaki Drive sinking profile 0 Tamaki Drive Pakanoa point Auckland port Port Cliff Road Cliff Road 2.4mm 0.4mm -3mm per year Pakanoa point Sinking at 2.7mm per year This mini map of the stretch of coast from Aucklands port along the popular beaches of Tamaki Drive shows where the land is sinking and therefore more vulnerable to sea level rise. The chart on the right shows that the rate varies widely even along a small length of coastline - at the port, its 2.4mm a year, while its 2.7mm near the pier at Pakanoa point and just 0.4mm at Cliff Road (which is further west along the harbour, past St Heliers). The seaside road that carries commuters from Mission Bay and St Heliers to the central city already experiences floods today. The Searise researchers arent sure why so much of Aucklands coast is sinking, but the pattern is similar in several other parts of the citys coast. I think a lot of people were surprised to see how much the data suggests that Auckland is actually subsiding... not as fast as the eastern portion of the North Island, but certainly subsiding, says Levy. That subsidence is bringing sea level rise forward by a decade or more, he says. Petone 2.3mm per year 2.8mm -3.8mm Lowry Bay -3.7mm Sinking by 3.8mm Lowry Bay per year Sea level rise projections at Lowry Bay Low emissions SSP2-4.5 High emissions SSP3-7.0 2m sea-level rise 36cm rise happens 25 years earlier with vertical movement 0.5 no movement 2040 2120 2040 2120 2080 2080 Sea level rise projections at Lowry Bay Petone Low emissions SSP2-4.5 2m sea-level rise with vertical movement 2.8mm 2.3mm per year 0.5 no movement 3.8mm 2080 2040 2120 High emissions SSP3-7.0 2m 36cm rise happens 25 years earlier 3.7mm Lowry Bay Sinking by 3.8mm Lowry Bay per year 0.5 2040 2080 2120 Sea level rise projections at Lowry Bay Petone Low emissions SSP 2-4.5 2.8mm 2m sea-level rise 2.3mm per year with vertical movement with vertical movement 0.5 3.8mm no movement 2040 2080 2120 High emissions SSP 3-7.0 3.7mm 36cm rise happens 25 years earlier than expected 2m Lowry Bay Lowry Bay Sinking by 3.8mm 0.5 per year 2040 2080 2120 Sea level rise projections at Lowry Bay Petone Low emissions SSP2-4.5 2m sea-level rise 2.8mm 2.3mm per year with vertical movement no movement 0.5 3.8mm 2040 2080 2120 High emissions SSP 3-7.0 2m 3.7mm Lowry Bay 36cm sea-level rise happening 25 years earlier than expected Sinking by 3.8mm Lowry Bay 0.5 per year 2040 2080 2120 Lowry Bay in Lower Hutt is sinking at 3.8mm a year, coincidentally about the same amount (3.5mm) that the sea around New Zealand is rising. Add the two together and you get effectively double the global average rate of sea level rise. The graphs on the right show sea level projections for Lowry Bay, with and without the land sinking. In both graphs, the bottom line shows how much sea level rise is projected to happen anyway. The top line shows whats projected to happen with the sinking factored in. The gap between the lines represents the difference between how long you would have thought it would take to reach a certain threshold of sea level, based on national average projections, and how long it will actually take, using the land subsidence data. There are two emissions scenarios shown - a world of middling climate pollution, where the world takes some climate action but misses its Paris Agreement targets (top graph). The second is a more pessimistic (but happily less likely) scenario, where collective action fails and global heating reaches 3.8-4.2C. So how much difference does the land sinking make? In the high emissions scenario, it means 36cm of sea level rise (a damaging amount for Wellington) arrives 25 years earlier than would have been expected. The area should expect 6 to 11 extra centimeters of sea level rise by 2100 because it is slowly sinking New Brighton Avon Heathcote estuary Southshore Mount Pleasant New Brighton/Southshore sinking profile 0 -1mm per year Bridge St Marine Pd 0.75mm Sinking at 0.8mm per year Golf club The area should expect 6 to 11 extra centimeters of sea level rise by 2100 because it is slowly sinking New Brighton Marine Pd end Bridge St Southshore New Brighton/Southshore sinking profile 0 Golf club 0.3mm -1mm per year Marine Pd end Bridge St Sinking at 0.75mm 0.8mm per year New Brighton/Southshore profile Golf Club 0 The area should expect 6 to 11 extra centimeters of sea level rise by 2100 because it is slowly sinking Golf club 0.3mm -1mm per year New Brighton Marine Pd end Bridge St Sinking at 0.75mm Marine Pd end 0.8mm per year Bridge St Southshore New Brighton/Southshore sinking profile Golf Club 0 The area should expect 6 to 11 extra centimeters of sea level rise by 2100 because it is slowly sinking Golf club 0.3mm -1mm per year New Brighton Marine Pd end Bridge St Sinking at 0.75mm Marine Pd end 0.8mm per year Bridge St Southshore New Brighton in Christchurch shows some evidence of gradual sinking, but it is much less dramatic than Wellingtons Lowry Bay or even Tamaki Drive in Auckland. This means that the beach is projected to experience roughly the global average sea level rise, with a small amplification from land subsidence. In other words, if the residents were using the standard one-size-fits-all projections from the Ministry for the Environment or IPCC, they wouldnt be too far off. In their case, global heating is driving their oceans higher - without too much of a helping hand from sinking land. This mini-map shows that, even in relatively stable places, there will be local variation, as you can see from the difference between the Golf Club and Marine Parade. Otamarakau beach 5mm Otumoetai 1.3mm Mt Maunganui 1.2mm Tauranga Matata 2.9mm Sea level rise projections at Otumoetai, Tauranga Low emissions SSP2-4.5 High emissions SSP3-7.0 9 extra years to prepare for 50cm rise 1.5m sea-level rise no vertical movement 0.5 with movement 2040 2120 2040 2120 2080 2080 Sea level rise projections at Otumoetai, Tauranga Low emissions SSP2-4.5 1.5m sea-level rise Mt Maunganui no vertical movement Otumoetai 1.2mm 1.3mm 0.5 Otamarakau beach with movement 5mm 2080 2040 2120 Tauranga High emissions SSP3-7.0 1.5m 9 extra years to prepare for 50cm rise Matata 2.9mm 0.5 2040 2080 2120 Sea level rise projections at Otumoetai, Tauranga Low emissions SSP2-4.5 Otumoetai Mt Maunganui 1.5m sea-level rise 1.3mm 1.2mm no vertical movement Otamarakau beach + 0.5 5mm with movement 2040 2080 2120 Tauranga High emissions SSP3-7.0 1.5m 9 extra years to prepare for 50cm sea-level rise Matata 2.9mm 0.5 2040 2080 2120 Sea level rise projections at Otumoetai, Tauranga Low emissions SSP2-4.5 Mt Maunganui Otumoetai 1.5m sea-level rise 1.2mm 1.3mm no vertical movement Otamarakau beach with movement 0.5 5mm 2040 2080 2120 Tauranga High emissions SSP3-7.0 1.5m 9 extra years to prepare for 50cm sea-level rise by 2080 Matata 2.9mm 0.5 The coast of the Tauranga suburb of Otumoetai is fairly stable or rising slightly, meaning that - again - the global average sea level rise rate is about correct for this location. On average land in Tauranga rising slightly, though not as quickly as the ocean. Because of that: You've got a little bit more time to plan because geology has given you a little bit more leeway, says Levy. However Tauranga locations vary. The Port, for example, is sinking, being built on fill. Further along the coast at Otamarakau beach, the data shows one of the fastest upwards land movements in the country, at 5mm per year. As with Lowry Bay, Wellington, the graphs on the right show the preparation gap or how much faster or slower the ocean reaches a certain level. In this case, they show that the suburb of Otumoetai looks set to get some extra time - nine more years before 50cm of sea level rise hits under a high emissions scenario. Westshore beach 2.9mm per year Airport built in a wetland and rapidly, sinking. This area is really vulnerable to sea level rise Napier Airport Sea level rise projections at Westshore beach, Napier Low emissions SSP2-4.5 High emissions SSP3-7.0 2m sea-level rise 36cm rise 3 decades earlier with vertical movement 0.5 no movement 2040 2120 2040 2120 2080 2080 Sea level rise projections at Westshore, Napier Wests hore Low emissions SSP2-4.5 2.9mm per year 2m sea-level rise Airport built in a wetland and rapidly sinking. This area is really vulnerable to sea level rise with vertical movement Napier Airport 0.5 no movement 2080 2040 2120 High emissions SSP3-7.0 2m 36cm rise 3 decades earlier 0.5 2040 2080 2120 Sea level rise projections at Westshore beach, Napier Westhore beach 2.9mm per year Low emissions SSP2-4.5 Airport built in a wetland and sinking rapidly. This area is really vulnerable to sea level rise 2m sea-level rise Napier Airport with vertical movement 0.5 no movement 2040 2080 2120 High emissions SSP3-7.0 36cm rise 3 decades earlier, a 75% increase for 2080 2m 0.5 2040 2080 2120 Sea level rise projections at Westshore, Napier Low emissions SSP2-4.5 Westshore 2m sea-level rise 2.9mm per year with vertical movement Airport built in a wetland and sinking rapidly. This area is really vulnerable to sea level rise Napier Airport no movement 0.5 2040 2080 2120 High emissions SSP3-7.0 2m 36cm sea-level rise happens 3 decades earlier, a 75% increase on what previously expected for 2080 0.5 2080 2040 2120 Much of Napier is built on reclaimed land, making it vulnerable to sea level rise and subsidence. The Searise estimates suggest Westshore, near the airport, is sinking by 2.9mm a year, almost doubling the effects of sea level rise. Again, the graphs on the right show what that does to Napiers preparation time, under both middling and high emissions futures. Under the high emissions scenario, 36cm of sea level rise happens three decades earlier than it would have without that local subsidence. All graphs are based on NZ Searise project ( which includes scientists from GNS Science, Niwa and Victoria University ) data with Stuff analysis. Together, we can keep it that way. Like you, we want a better future for all New Zealanders. We want to know how the Government plans to get to zero carbon, and how the Climate Change Commission's advice will be activated. Our specialist climate desk is committed to covering this global crisis with a unique mix of rigour, reality and resolve. We're asking for your support to ensure this essential work remains accessible to everyone. If you're concerned about the climate, please become a Stuff supporter today. 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