Natural Barriers to Natural Disasters

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    Natural Barriers to Natural DisastersAuthor(s): ALEXANDER M. KERR and ANDREW H. BAIRDSource: BioScience, 57(2):102-103. 2007.Published By: American Institute of Biological SciencesDOI:

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  • Viewpoint

    Coastal forests, according to var-ious reports, ameliorated the deathtoll and damage caused by the Decem-ber 2004 tsunami in the Indian Ocean.Many organizations have therefore ad-vocated the replanting of forests as anatural barrier against tsunamis. For example, the World Conservation Union(IUCN) is promoting Mangroves forthe Future, a $62 million program thataims to build natural barriers of man-groves in 12 countries in Asia and Africa.Discussions to date within the conser-vation community have concentratedon how to make these replanting pro-grams successful. A far more importantconsideration, however, is whether ornot these barriers will be effective againstfuture tsunamis.

    The science upon which these coastalreforestation projects are based is un-convincing; nearly all of the primary accounts supporting a mitigating rolefor vegetation during the 2004 tsunamiare anecdotal. Quantitative support forthe mitigation hypothesis has beenmixed. For example, Danielsen and col-leagues (2005) concluded that coastalforests in Tamil Nadu, India, attenuatedtsunami-induced waves and protectedshorelines against damage. However, areanalysis of data from the same area(Kerr et al. 2006) found no relationshipbetween human mortality and the ex-tent of forests fronting coastal hamletswhen controlling for differences in ele-vation and distance from shorenotsurprisingly, more vegetation can front ahamlet lying farther inland than one ad-jacent to the coast. Furthermore, more re-cent work, including data from 57 sitesthroughout the Indian Ocean, concludedthat the distance the tsunami penetratedwas best explained by distance from theearthquake epicenterthat is, waveheight at the coastand features of near-shore bathymetry (Chatenoux and Pe-

    duzzi 2007). Most important, coastal veg-etation had no mitigating effect on in-undation distance. We do not argue thatsuch an effect does not exist; more dataand more powerful approaches may wellfind an association. Certainly, the pro-tection afforded by a shoreline of densetrees appears substantial for typicalstorm-generated waves (Massel et al.1999); however, it decreases monotoni-cally with increasing wave energy. Forexample, the tsunami following the 1883

    eruption of Krakatoa penetrated 8 kilo-meters of full-canopy rainforest (Simkinand Fiske 1983).

    Natural Barriers to Natural Disasters


    102 BioScience February 2007 / Vol. 57 No. 2

    Alexander M. Kerr (e-mail: works at the Marine

    Laboratory, University of Guam, Mangilao,

    Guam 96913. Andrew H. Baird (e-mail: is with the Australian

    Research Council Centre of Excellence for Coral

    Reef Studies, James Cook University, Townsville,

    Queensland 4811, Australia.

    View looking northwest from the bridge in the village of Lhoknga, Aceh, Indonesia. Top: November 2000.Bottom: March 2005. Almost all coastal vegetation up to 4 kilometers inland was destroyed by the tsunamiof 26 December 2004.












  • This lack of quantitative support forthe mitigation hypothesis has not damp-ened the enthusiasm with which envi-ronmental organizations, governments,and some scientists are promoting theefficacy of green belts and bufferzones in averting future catastrophes.Government enforcement of these bufferzones is a cause of major social injusticeinvolving the eviction of people fromthe coast and the failure to provide financial support for those wishing torebuild their homes within these zones( We are concernedthat promoting green belts as barriers,particularly in preference to tsunamiearly-warning systems, as suggested bysome scientists (e.g., Dahdouh-Guebas etal. 2005), may lead to substantial loss oflife in a future event. As we argue above,these barriers have yet to be proven effective, and therefore may encourage afalse sense of security.

    Consequently, these schemes directtime and money away from more effec-tive measures, such as well-coordinatedearly-warning systems, community ed-ucation, and emergency planning. In-credibly, more than 18 months after theIndian Ocean tsunami, the Indonesiangovernment has yet to deploy an early-warning system south of Sumatra. Thetsunami of 17 July 2006 in Java demon-strated the tragic consequences of thisoversight. Tremors from the earthquakethat preceded the tsunami were felt, andthe trough of the tsunami reached thecoast before the crest, causing a telltaledrawdown (a seeming drop in the sealevel), yet many people did not think torun. Government officials were givenprecise warnings of the likelihood of thetsunami and failed to act. Clearly, ed-ucation efforts in Indonesia have been inadequate.

    Coastal vegetation, such as mangroves,can provide coastal communities withmany valuable goods and services, andthe protection and rehabilitation of theseecosystems is an endeavor we whole-

    heartedly support. However, in the absence of adequate studies, the signifi-cance of vegetation in ameliorating mor-tality and damage from future tsunamisremains an open question, and thus anyrole the hypothesis plays in environ-mental advocacy and in formulating pol-icy could prove disastrous.

    References citedChatenoux B, Peduzzi P. 2007. Impacts from the

    2004 Indian Ocean tsunami: Analysing thepotential protecting role of environmentalfeatures. Natural Hazards 40: 289304.doi:10.1007/s11069-006-0015-9

    Dahdouh-Guebas F, Jayatissa LP, Di Nitto D,Bosire JO, Lo Seen D, Koedam N. 2005. Howeffective were mangroves as a defence against

    the recent tsunami? Current Biology 15:R443R447.

    Danielsen F, et al. 2005. The Asian tsunami: Aprotective role for coastal vegetation. Science310: 643.

    Kerr AM, Baird AH, Campbell SJ. 2006. Com-ments on Coastal mangrove forests mitigat-ed tsunami by K. Kathiresan and N. Rajen-dran. Estuarine, Coastal and Shelf Science 67:539541.

    Massel SR, Furukawa K, Brinkman RM. 1999.Surface wave propagation in mangroveforests. Fluid Dynamics Research 24:219249.

    Simkin T, Fiske RS. 1983. Krakatau 1883: The Volcanic Eruption and Its Effects. Washington(DC): Smithsonian Institution Press.

    doi:10.1641/B570202Include this information when citing this material.

    Viewpoint February 2007 / Vol. 57 No. 2 BioScience 103

    View looking south over the villages of Lhoknga andLampuuk Aceh, Indonesia. Top: November 1987.Bottom: December 2005. Almost all coastal vegetationwas stripped away by the tsunami of 26 December 2004, and every structure in both villages was entirelydestroyed, with the exception of the mosque (not visible).







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