[Radix] Tsunamis and Coastal Tree Barriers

[Ilan Kelman]

To Radix:




A press release was issued about an upcoming publication
that suggests that planting trees along coasts is not a good idea for reducing
tsunami damage.  If that were taken as a
straightforward and definite statement, which would be inappropriate, it could have
significant and detrimental implications for coastal management.




I provide below my full reaction to the press release
followed by the press release itself.  I
hope that this will provide a more balanced view of the topic, rather than
leaping to conclusions.




Best wishes,




Ilan 



----------

 

The press release below on coastal tree barriers and
tsunamis raises numerous concerns which are reflective of the journalistic
nature of the article, not of the science that is being reported.  My points are:

 

1. The statement that "there is, as yet, no evidence
that coastal tree belts can provide meaningful protection against a tsunami or,
for that matter storm surges produced by cyclones" is an
exaggeration.  The scientifically correct
interpretation of the data available is that there is not enough evidence to
prove that statement conclusively.  Yet,
conversely, there is not enough evidence to claim that coastal tree belts do
NOT provide meaningful protection. 
Overall, we do not have enough evidence to make a claim either way and
that is the message that ought to be highlighted.

 

2. The statement "it would be extremely dangerous to
rely on tree planting alone to shield coastal communities in the event of
future tsunami or storm surges" is entirely correct.  That, in fact, is exactly the same message
which has been promoted for decades regarding all forms of flood risk
reduction:  that relying on structural
measures increases flood vulnerability and risk in the long-term http://www.ilankelman.org/miscellany/StructuralDefences.rtf  However, the coastal tree barrier press
release misses the point that coastal tree barriers have the potential for
doing much more than simply address flood risk reduction. Ample evidence
exists, such as from Vietnam, that if appropriately implemented as a
development programme, coastal mangroves can not only reduce flood risk but
also promote sustainable livelihoods. 
That element is missing from the press release:  the debate should not be about flood
protection, but should be about disaster risk reduction, development, and sustainable
livelihoods, all addresses simultaneously to complement each other--as
evidenced by decades of research and practice including much (although far from
all) post-tsunami work.

 

3. Look carefully at the language in the press release:  "barriers", "shield",
"protection".  This is typical
of the technocratic, humanity-against-nature language which is highly
culturally biased yet which dominates much disaster risk reduction discourse,
sending inaccurate messages regarding disaster risk reduction, development,
environmental management, sustainability, and livelihoods.  Instead, it is more helpful and more accurate
to discuss how coastal ecosystems, including those with trees, could be used to
support livelihoods, development, and sustainability, including disaster risk
reduction--with extensive evidence and case studies from research and
practitioner publications.

 

4. The variables quoted as being important are indeed
important, but connections amongst those variables (causations and
correlations) need to be considered too. 
For example, the presence of coastal tree barriers might affect distance
of a village from the shore and hence the height of the village above sea
level.  That is, by planting coastal tree
barriers, it is conceivable, although certainly not definite, that villages
might end up being set back farther from the shore and/or farther above sea
level--or the villages might end up closer to the shore and/or closer to sea
level.  If this speculation is proven either
way, then coastal tree barriers would have a direct link to tsunami and storm
surge damage, either increasing or reduction the damage.

 

5. The "shape of the seabed in concentrating the
tsunami's power" is mentioned but not the fact that most damage from
tsunamis comes from waves that are breaking or that have just broken.  If coastal tree barriers cause waves to break
earlier or cause a significant proportion of the force of the breaking wave to
be spent before reaching human settlements--and these statements are entirely
speculation--then coastal tree barriers would reduce damage.  The issue of where and how the waves break,
and how coastal tree barriers affect that, including resulting debris in the waves, needs to be addressed in more
detail.

 

6. The maximum height of the waves is also important,
especially at the coast. Some places in Aceh apparently experienced tsunami
heights of over 30 metres. Perhaps little could be done to avert damage at the shoreline in such
circumstances. But that says little about the impacts of coastal trees on the
velocity, debris content, breaking characteristics, and inundation zone of
tsunamis or storm surges in cases where the water's height is less than the
coastal vegetation's height.

 

Two more general points:

 

7. It is disappointing that tsunamis and storm surges are
not separated more.  There is far more
evidence for storm surges than for tsunamis and that should be acknowledged.

 

8. This press release focused on "coastal tree
barriers" but there is a danger that this phrase has different meanings to
different people and could be interpreted as any coastal ecosystem, especially
with the press release's inclusion of the phrase "a barrier of trees or
coastal vegetation".  I agree that
the evidence for or against "coastal tree barriers" is particularly sparse,
but (i) coastal tree barriers are only one component of coastal ecosystems with
trees and (ii) the evidence is far more conclusive for a wide range of coastal
ecosystems supporting disaster risk reduction, development, environmental
management, sustainability, and livelihoods.

 

My comments should not in any way be taken as a scientific
statement about Baird et al.'s work.  I
am reacting to the press release, not to the full study which apparently has
not yet been published.  A few years ago,
a similar media article made Baird et al.'s comments look unscientific, but when
I read the full scientific papers, I had no scientific critiques about what was
published in the academic journals. 
Instead, Baird et al. provided insightful remarks based on the evidence
that they had collected.  Similarly, the
critiques in the press release of other work have scientific legitimacy and
ought to be discussed further, but they fail to give the full story or to
account for all the evidence across many studies.  The full report, though, is presumably much
better in doing that.

 

Overall, my concern here is science communication in terms
of the messages being publicised and the scientific evidence being presented.

 

Ilan

 

-------------

 

http://www.igovernment.in/site/Coastal-tree-barriers-cannot-stop-tsunami-Experts/

Coastal tree barriers cannot stop tsunami: Experts

*A team of marine scientists has dismissed claims that
coastal tree barriers

can halt the might of a tsunami as 'false and dangerous'*

 

Published on 1/6/2009 12:40:21 PM

 

*Sydney:* A team of marine scientists has dismissed claims
that coastal tree

barriers can halt the might of a tsunami as 'false and
dangerous'.

 

Shortly after the fourth anniversary of the devastating
Indian Ocean

tsunami, which claimed nearly a quarter of a million lives,
researchers

issued a strong warning against coastal communities and
governments putting

their trust in mangrove and tree barriers erected as a means
of protection,

reports IANS.

 

"Following the tsunami scientific studies were released
which claimed that

the damage to coastal communities had been less in places
where there was a

barrier of trees or coastal vegetation," said Andrew
Baird of the ARC Centre

of Excellence for Coral Reef Studies and James Cook
University.

 

As a result there has been a lot of tree planting in coastal
areas affected

by the tsunami, in the hope it will protect coastal
communities in future

from such events, Baird added.

 

"However, these studies looked only at the presence or
absence of vegetation

and the extent of damage—and did not take account of other
important

variables, like the distance of a village from the shore,
the height of the

village above sea level or the shape of the seabed in
concentrating the

tsunami's power," he said.

 

The study concludes there is, as yet, no evidence that
coastal tree belts

can provide meaningful protection against a tsunami or, for
that matter

storm surges produced by cyclones, such as the surge that
followed Cyclone

Nargis in Myanmar last year which killed over 1.5 lakh
people.

 

As a result it would be extremely dangerous to rely on tree
planting alone

to shield coastal communities in the event of future tsunami
or storm

surges, they warn—and doing so could lead to further
tragedies, an ARC

release said.

 

The findings have major implications for civil defence and
emergency

planning, the cost of restoring affected regions and in
minimising the death

and destruction suffered by some of the poorest communities
in the world,

the team says.

 

Their study is scheduled for publication by the United
Nations Environment

Programme.


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