Understanding coastal hazard risks from climate change is the first step in talking about how we can adapt to them.


Our rising sea levels and sinking land 

Sea levels have risen around 15 centimetres over the last 30 years in Ōtautahi Christchurch, and we expect to see a further 14 to 23 centimetres by 2050, and between 38 centimetres and 1 metre by 2100.  

As this happens, low-lying areas will experience deeper flooding more often. The water may also stay around for longer as groundwater levels rise and it gets harder for surface water to drain away into the soil. Areas at risk of erosion are also likely to lose land at a faster rate as sea levels rise, because tides and waves will reach further inland.  

Some parts of our district are also sinking due to a process called vertical land movement. Where this is happening, it's been more pronounced following the Canterbury Earthquake Sequence, with some areas sinking faster than 7 millimetres a year. 

Read more about the three main coastal hazards made worse by climate change and sea-level rise below, or, if you'd like a summary, read our coastal hazards fact sheet [PDF, 1 MB].

Coastal flooding is a natural event that happens when normally dry, low-lying land is flooded by the sea. 

Coastal flooding normally happens during storms, when low-pressure weather systems, large waves driven by strong winds, and tides combine to raise water levels. The worst flooding happens when larger-than-normal high tides and storms with heavy rainfall arrive at the same time.

Rising sea levels can also lead to ‘sunny-day flooding’, which is when high, spring and king tides cause flooding without a storm.  

As the level of the sea rises, land that currently floods during storms or extreme high tides may flood more often and deeper. Slightly higher areas or low-lying areas further inland may also begin to flood over time.

Coastal erosion is a natural and ongoing process that happens when the sea wears away the land. Some coastal areas undergo short-term periods of erosion but then recover, while others keep eroding with no cycle of recovery. 

The rate of erosion depends on the: 

  • Ocean conditions, like waves, tides, storm surge, and currents, which are all impacted by climate change.
  • How abundant the supply of sediments, like sand, is to a location.
  • How the land is moving up or down through a process called vertical land movement.
  • How sea levels are rising as a result of climate change.
  • The landscape type – for example, beaches and rocky cliffs are impacted by erosion in different ways and to different extents.  

Over years and decades, depending on the landscape type and the balance of short-term erosion events and recovery periods, some coastlines grow out towards the sea, some stay about the same, and some retreat landward.  

Erosion is more likely to happen as sea levels rise and storms become more frequent and severe. Our coastlines are also less likely to have time to recover between erosion events. This means that, in most cases, the growth of our coastlines will slow or stop, and they'll then start to erode more quickly. 

Groundwater is the word used to describe the water that exists beneath the land's surface. Groundwater is much closer to the surface in some areas than others, particularly in low-lying areas around rivers, estuaries, and the sea.  

Groundwater levels naturally change over days, weeks, seasons, years, and during different tides. This connection between the sea and groundwater means that we expect climate change and rising sea levels to cause groundwater to rise closer to the surface in low-lying coastal areas.  

Changing weather patterns as a result of climate change may also cause less frequent, but more intense, rainfall. High groundwater makes it harder for rainwater to soak into the ground, which increases the likelihood of flooding during these rainfall or storm events. It also means the flood waters may stick around for longer, known as ponding. 

We have a big network of groundwater monitoring stations that help us see what's happening beneath the surface and identify areas that are at risk of rising groundwater levels. In general, areas that are most at risk from high groundwater are the same areas that are at risk from coastal flooding.

High groundwater tables also exist in other parts of the Christchurch district, further inland from the coast, but groundwater in these areas is not expected to be significantly impacted by sea-level rise.

Vertical land movement is generally caused by movements in the Earth’s crust. These upward or downward movements can be very fast, like during an earthquake, or slow and gradual. Local land movements can happen from other processes too, like liquefaction, which we've seen here in Ōtautahi Christchurch. 

A recent study by GNS Science [PDF, 1.6 MB] has shown that sea-level rise in some parts of Christchurch is happening up to twice as fast as previously thought, as a result of increased land subsidence following the Canterbury and Kaikoura earthquakes.

This means the impacts of sea-level rise – flooding, coastal erosion, and rising groundwater – will happen sooner, reinforcing the importance of planning for them now. 

It's common for land to keep sinking after large earthquakes. While there's no sign that subsidence has slowed down in Christchurch over the last decade, evidence from other parts of the world tells us that, eventually, the speed of vertical land movement will return to normal; however, it might take another few decades and will depend on whether we experience more large earthquakes.

Tsunamis can be classed as local, regional, or distant, depending on where they originate and how long it takes them to reach our coastal areas. 

A tsunami large enough to cause flooding of the land in Ōtautahi Christchurch could come from any of these sources.

Distant source tsunamis from around the Pacific Ocean pose the most frequent tsunami threat to Ōtautahi Christchurch.

Our Christchurch coastal hazards interactive map(external link) lets you explore how different areas across the Christchurch District may be affected by coastal hazards.

Or watch these easy-to-understand videos of why Christchurch and Banks Peninsula are at risk of coastal hazards and what we might expect to see happen over the next 20, 50 and 100 years as sea levels rise.

Coastal hazards

Information on coastal hazards was developed in collaboration with representatives from community groups with interests in technical hazard information and environmental issues. The assessment was completed by Tonkin + Taylor in 2021 and peer reviewed by Jacobs.

If you are interested in more detail, you can read the full report [PDF, 4.8 MB] and the summary report [PDF, 1 MB]. If you want to explore how coastal hazards will impact the district, check out our interactive online maps(external link).

Council has commissioned several coastal hazard assessments over the years. You can check out past assessments.

Vertical land movement

GNS Science completed studies in 2023, 2024 and 2025 on vertical land movement before, during and after the Canterbury Earthquake Sequence. These studies were jointly commissioned by Christchurch City Council and Environment Canterbury.

Check out our factsheet [PDF, 1.6 MB].

Technical reports

Understanding these hazards and how our district is at risk is an important part of adaptation planning. We have a range of technical reports and information about these hazards that we use to help inform the planning process.