Policy Research Working Paper 7596
Mangroves as Protection from Storm Surges in a Changing Climate
Brian BlankespoorSusmita Dasgupta
Glenn-Marie Lange
Development Data GroupSurveys and Methods Team &Development Research GroupEnvironment and Energy TeamMarch 2016
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Abstract
The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.
Policy Research Working Paper 7596
This paper is a product of the Surveys and Methods Team, Development Data Group; and the Environment and Energy Team, Development Research Group. It is part of a larger effort by the World Bank to provide open access to its research and make a contribution to development policy discussions around the world. Policy Research Working Papers are also posted on the Web at http://econ.worldbank.org. The authors may be contacted at [email protected].
Adaptation to climate change includes addressing sea level rise and increased storm surges in many coastal areas. Mangroves can substantially reduce the vulnerability of the adjacent coastal land from inundation and erosion. How-ever, climate change poses a large threat to mangroves. This paper quantifies the coastal protection provided by man-groves for 42 developing countries in the current climate, and a future climate change scenario with a one-meter sea level rise and 10 percent intensification of storms. The benefits of the coastal protection provided by mangroves are measured in terms of population and gross domestic product at a reduced risk from inundation; the loss of
benefits under climate change is measured as the increased population and gross domestic product at risk. The find-ings demonstrate that although sea level rise and increased storm intensity would increase storm surge areas and the amounts of built resources at risk, the greatest impact is the expected loss of mangroves. Under current climate and mangrove coverage, 3.5 million people and roughly $400 million in gross domestic product of are at risk. In the future climate change scenario, the vulnerable population and gross domestic product at risk would increase by 103 and 233 percent, respectively. The greatest risk is in East Asia, especially in Indonesia, the Philippines, and Myanmar.
MangrovesasProtectionfromStormSurgesinaChangingClimate
BrianBlankespoor1,SusmitaDasguptaandGlennMarieLange
Keywords:mangroves;climatechange;stormsurge;coastalprotection
JELclassification:Q54,Q57
1Authors names are in alphabetical order. The authors are respectively Environmental Specialist,WorldBank;LeadEnvironmentalEconomist,WorldBank;andSeniorEnvironmentalEconomist,WorldBank.
Wewould like to thank Chandra Giri (United States Geological Survey) for providing themangrovepresencedatanecessarytoconducttheanalysis.WeextendaspecialthankstoAnnaMcIvor(Universityof Cambridge) for her insight on the analysis, particularly the formulation of thewave attenuationfunctions.WealsothankMarkSpalding(UniversityofCambridgeandTheNatureConservancy)forhisguidanceonthemangroveresults,EdBarbier(UniversityofWyoming)forhisthoughtfulreviewofthisresearch,PeterMumby(UniversityofQueensland),andMikeBeck(TheNatureConservancy)fortheirinsights on this analysis. We are thankful to Zahirul Huque Khan (Institute of Water Modeling,Bangladesh)forsharingthetechnicalanalysisofmangroveafforestation inHatia island.WealsothanktheparticipantsoftheStateoftheKnowledgeoftheProtectiveServicesandValuesofMangroveandCoralReefEcosystems,organizedbyTheNatureConservancyandtheWorldBankWAVESPartnership,at theUniversityofCalifornia, SantaCruz,United States,December3 4, 2014.We also thank theparticipants of the presentation at the Association of American Geographers Annual Conference,Chicago,US,April25,2015.TheresearchwaspartiallyfundedbytheWealthAccountingandValuationofEcosystemServicesPartnership.
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1. Introduction
Adaptationtoclimatechangewillrequirelivingwithsealevelriseandincreasedstormsurgesin
many coastal areas (IWTC 2006; IPCC 2013; Rahmstorf 2007; ADB 2008; ScienceNow 2008;
Dasgupta andMeisner 2009a;WMO 2010;World Bank 2010a,World Bank 2010b). Coastal
protectionfromstormsurgeandfloodingispartlyprovidedbybuiltinfrastructure(Dasguptaet
al. 2010; World Bank 2010c; Nicholls et al. 2010). Mangroves2 are a form of natural
infrastructure thatalsoprovidescoastalprotection in tropical regions.Theprotective roleof
mangroves and other coastal forests and trees against coastal hazards has received
considerableattentionintheaftermathofthe2004IndianOceantsunami.Thispaperdescribes
the extent of coastalmangrove forests in developing countries with previous exposure to
tropicalcyclones,howmangroveswillbeaffectedbyclimatechange,thegeographicareaand
humanresourcesatriskduetolossofcoastalprotectionfrommangrovesinachangingclimate,
andthepotentialforadaptation.
The idea that mangroves may protect coastal communities from coastal hazards (coastal
erosion,tidalbores,windandsaltspray,cyclones,etc.)iswellknownintropicalcoastalecology
andincreasinglybycoastalmanagers(Chapman,1976;UNEPWCMC,2006;Doneyetal.2012;
Waite et al. 2014). Variousmodeling andmathematical studies have shown thatmangrove
forestscanattenuatewaveenergy(Brinkmanetal.,1997,Mazdaetal.1997,2006;Masselet
al.,1999;Quarteletal.,2007,Barbieretal.2008,Gedanetal.2011;Zhangetal.2012;McIvor
et al. 2013; Liu et al. 2013; Pinsky et al. 2013). However, these studies indicate that the
magnitudeoftheenergyabsorbedstronglydependsonforestdensity,diameterofstemsand
2 Mangroves are salttolerant evergreen forests found along sheltered coastlines, shallowwaterlagoons,estuaries,riversordeltasin124tropicalandsubtropicalcountriesandareas(Tomlinson1986;Ellison and Stoddart 1991).A mangrove has been defined as a tree, shrub, palm or ground fern,generallyexceedingmorethanhalfameterinheight,andwhichnormallygrowsabovemeansealevelin the intertidalzonesormarinecoastalenvironments,orestuarinemargins (Duke1992). The termmangrove describes both the ecosystem and the plant families that have developed specializedadaptations to live in this tidal environment. The mangrove ecosystem represents an inter phasebetweenterrestrialandmarinecommunities,whichreceiveadailyinputofwaterfromtheocean(tides)andfreshwater,sediments,nutrientsandsiltdepositsfromuplandrivers.Mangrovesmaygrowastreesor shrubsaccording to theclimate, salinityofwater, topographyandedaphic featuresof thearea inwhichtheyexist.
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roots, forest floor shape,bathymetry, spectral characteristicsof the incidentwaves,and the
tidalstageatwhichthewaveenterstheforest.Eventhoughadditionalstudiesareneededto
definethespecificdetailsandlimitsofthisprotectivefunction,expertsandscientistsagreethat
coastal forestbelts, ifwelldesignedandmanaged,havethepotentialtoactasbioshields for
theprotectionofpeopleandotherassetsagainst theabovementioned coastalhazardsand
sometsunamis(FAO,2007;DasandVincent,2009;Arkemaetal.2013).
The latestglobalestimatesofthetotalareaofmangrovesrangefromapproximately137,000
sq. km (Giri et al 2010) to 150,000 sq. km (Spalding et al 2010). Over the past century,
mangrove forestcoverhasdeclinedsignificantly.Although figuresarenotavailable forglobal
mangrove forest cover loss over the century, estimates indicate the amount of loss to be
approximately35,600 squarekilometers from1980 (FAO2007;Spaldingetal2010),withan
averageannual loss rateof1.04percent from1980 to2000,and0.66percent from2000 to
2005.Ratesofaverage lossmayhave stabilizedordeclined furtherbetween2000and2012
withafewexceptions,mainlyinSoutheastAsia(HamiltonandCasey2014).3
Most of this loss is a result ofmangrove clearing for aquaculture, tourism, industrial/urban
development, and overexploitation ofmangrove timber. In addition, urban and industrial
pollution has contributed to degradation. (For example, see Tanaka 1995; Primavera 1997;
Wolanskietal.2000;SaitoandAlino2008;Girietal.2008;FekaandAjonina2011;Shahbudin
etal.2012;Munjietal.2014;Nguyen2014.)Whilesignificantlossesduetohumanactionsare
likely to continue in the future, it is projected that stresses onmangrovesmay be further
aggravatedinthe21stcenturyduetoclimatechange.Continuationofthepresentrateofglobal
warmingmay even threaten the survival ofmangroves. Climate change poses a number of
threats to mangroves: rise in sea level, rise in atmospheric CO2, rise in air and water
temperature, and change in frequency and intensity of precipitation/storm patterns due to
climatechange(discussedinAlongi2008).Amongthesethreatsfromclimatechange,sealevel
3Dataforextendedperiodsareavailableforsomecountries.Forexample,coastaldevelopmentinthePhilippineshas ledtomorethana50percent lossofmangrovessince19
