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The Indian Ocean Tsunami and Sea Level Rise: Lessons to be Learned

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  • mtneuman@juno.com
    THE AUSTRALIA INSTITUTE The Indian Ocean Tsunami and Sea Level Rise Lessons to be Learned There has been much recent discussion in the media concerning both
    Message 1 of 1 , Jan 8, 2005

      The Indian Ocean Tsunami and Sea Level Rise
      Lessons to be Learned

      There has been much recent discussion in the media concerning both the
      tragic events
      in the Indian Ocean and sea level rise associated with global warming.
      They are of
      course not directly linked, but there are important lessons to be learned
      from the
      tsunami for coping with long-term sea level rise, especially in low-lying
      regions in the
      Indian and Pacific Oceans.

      One obvious difference between a tsunami and global sea level rise is the
      duration of
      the events. The Indian Ocean tsunami travelled from its source (an
      earthquake off
      Sumatra) to most of the regions it devastated in under three hours. The
      effect on those
      living on the shore was even more rapid - they had only minutes to react
      to the
      oncoming waves. In comparison, the effects of climate change are much
      slower -
      significant changes only happen over decades. However, probably the most
      difference is that, while a tsunami dies down completely in a day or two,
      sea level rise
      will be with us for many centuries.

      Tsunamis may also be much higher than the sea level rise that we expect
      to occur
      during the present century. While the Indian Ocean tsunami was only a
      metre or so in
      height as it travelled across the oceans,1 there are reports of it being
      amplified to many
      metres by the time it reached the land. On the other hand, the
      Intergovernmental Panel
      on Climate Change has estimated that the global sea level will rise by
      0.1- 0.9 of a
      metre by 2100, relative to the level in 1990.2 Although even the higher
      of these
      estimates may sound small, the effect on communities living on low- lying
      land would be devastating as 100 million people live within about one
      metre of the
      present sea level.3

      It is instructive to look at two regions that have previously received
      attention regarding the effects of future sea level rise: Bangladesh and
      the Maldives.
      The populous low-lying land of the deltaic regions of Bangladesh will
      suffer severely
      from sea level rise � it has been estimated that a 1.5 metre rise in sea
      level wo uld
      affect 17 million people.4 So why was the impact of the recent tsunami on
      this country
      so small? There are a number of reasons. Firstly, the wave that
      propagated northwards
      to Bangladesh appears to have been weaker,5 possibly due to the shape of
      the original
      earthquake zone.6 Secondly, much of the energy of the arriving tsunami
      dissipated in the large expanse of relatively shallow water offshore,7
      and thirdly, prior
      to the tsunami some 2000 multi-storied shelters had been installed to
      protect the
      population from cyclones and storm surges.8 Of course, none of these
      factors will be
      any protection against the impending sea level rise due to global

      The Maldives, on the other hand, suffered substantial damage and loss of
      life (around
      70 people perished and 11,000 were displaced).9 The height of the tsunami
      was about
      1 metre10 while 80% of the Maldives are less that one metre above normal
      sea level11
      and the highest point is only 2.4 metres above sea level.12 The resulting
      gives us a much better appreciation of the probable effects of sea level
      rise on such
      low- lying coastal communities.

      While we can learn a little about the likely effects of sea level rise
      from the tragic
      events of the past weeks, there is another vitally important message that
      should not be
      overlooked - that these events offer a unique opportunity. The tsunami
      has cleared
      much of the infrastructure from regions threatened by future sea level
      rise. Rebuilding
      of this infrastructure will need to proceed speedily in order for the
      many displaced
      people to return to more normal lives. There is a danger that
      redevelopment will occur
      on the same sites, with any future tsunami risk being accommodated
      through a
      combination of a warning system and a network of disaster shelters.

      It is, however, of the utmost importance that any rebuilding takes
      account of expected
      future sea level rise.

      Sea-level rise has two effects on a shoreline. On a hard (e.g. rocky)
      shore, the water
      surface simply moves up the sloping beach. However, on sandy shorelines,
      the beach
      and dune system is actually eroded, causing additional shoreline retreat.
      In the first
      case, the position of the new shoreline may be estimated simply from the
      rise in sea
      level, while the second case is far more complicated and requires
      knowledge of the
      way in which the coastal morphology responds. A crude rule of thumb is
      that, for
      every centimetre of sea level rise, the shoreline retreats by one

      Once these processes are reasonably well understood, a sound strategy is
      that of
      managed retreat, whereby development is restricted within a certain
      distance of the
      present shoreline, determined by the expected shoreline movement during
      the life of
      the structure.14 These set-backs may be supplemented by density
      restrictions and
      �rolling easements� that allow development to be pushed back as sea
      levels rise.
      Already some developed and developing countries have adopted suc h
      including no-build zones and set-backs of 50 metres or more.

      The tragic events of the past week therefore offer the opportunity for
      large coastal
      regions in and around the Indian Ocean to be redeveloped in a way that
      appropriate protection from sea level rise during the coming centuries. A
      wide range
      of expertise is required for this, including sea level scientists,
      geomorphologists, risk
      analysts and coastal planners - some of whom could and should be provided
      by the
      region�s richer neighbours.

      1 http://www.pmel.noaa.gov/tsunami/tidegauge200441226.html (Maldives);
      http://www.noaanews.noaa.gov/stories2004/s2358.htm (Cocos Islands)
      2 http://www.grida.no/climate/ipcc_tar/wg1
      3 http://www.marine.csiro.au/LeafletsFolder/45slevel/45.html
      4 http://www.grida.no/climate/vital/33.htm
      5 http://www.ppk.itb.ac.id/aceh/simulasi_tsunami_aceh.htm
      7 http://independent-bangladesh.com/news/jan/01/01012005mt.htm#A5
      8 http://www.guardian.co.uk/worldlatest/story/0,1280,-4703411,00.html
      9 http://en.wikipedia.org/wiki/2004_Indian_Ocean_Earthquake
      10 http://www.pmel.noaa.gov/tsunami/tidegauge200441226.html
      11 http://www.environment.gov.mv/climate.htm
      12 http://www.gesource.ac.uk/worldguide/html/950_map.html
      13 http://www.physicstoday.org/pt/vol-57/iss-2/p24.html
      14 http://www.grida.no/climate/ipcc_tar/wg2/301.htm#663

      7 January 2005
      The Australia Institute
      Innovations Building
      Australian National University
      Canberra, ACT, 0200
      (61) (2) 6125 1270
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