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Climate change and sea-level rise – what can we expect?

Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 01 December 2010

Extract from: Enviroworks – the City of Cape Town environmental newsletter

Due to Cape Town’s extensive coastline, sea-level rise associated with climate change poses a major threat to this prominent coastal city.

Three different scenarios

In order to predict and manage sea level rise, the City of Cape Town uses a computerised model called the GIS Inundation Model. This model uses long-term sea-level records, photographic images, and actual measurements of previous storms to predict the run-up of storm surges over the next 25 years. This model also factors in the gradual rise in the sea level to determine these predictions. Based on this information, the GIS Inundation Model indentifies three potential levels of inundation due to storm surges.

What does this mean for our coast and our city?

The three scenarios may be translated as follows:

Blue: There is a 95% chance that this area will be temporarily inundated over the next 25 years. This will take place along areas of coastline that are sheltered (such as Hout Bay). Within this particular zone, there is approximately R4.9 billion worth of property and infrastructure.

Red: There is an 85% chance that this area will be temporarily inundated over the next 25 years. This will take place along areas of coastline that are exposed (such as Kommetjie). Within this particular zone, there is approximately R20.2 billion in property and infrastructure.

Orange: There is a 20% chance that this area will be temporarily inundated over the next 25 years. This will take place along areas of coastline that are very exposed (such as Sea Point). Within this particular zone there is approximately R11 billion worth of property and infrastructure.

The GIS Inundation Model has also been used to investigate the long-term impacts (100 years into the future) of the complete melting of the polar ice sheets as well as the expansion of the world’s oceans due to global warming. The model identified the following three potential scenarios below:

08m mean sea-level rise

16m mean sea-level rise

20m mean sea-level rise

What can we do to be more resilient to sea-level rise?

Through learning from the past, we must make the right choices now. These choices must be in the best interests of all, as opposed to the interests of only a few. Here are some of the actions needed to manage sea-level rise:

  • The rehabilitation, protection and management of our coast as a functional natural system, as this system is the best protection against the effects of sea-level rise.
  • The establishment of a coastal protection zone to ensure its conservation, and the promotion of a ‘no regrets’ approach to future coastal planning.
  • The building of the City’s coastal engineering and disaster management capacity, and the protection and rehabilitation of natural coastal ecosystem.
  • The monitoring of changes in the coastline; and
  • Ensuring that the private sector, communities and individuals are well informed, accountable and responsible.

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