Rising Sea Level Due to Climate Change in Playa Grande, Las Baulas National Park, Costa Rica - Drews & Fonseca 2009

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Carlos Drews & Ana Fonseca


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Produced by Communications Department

WWF Central America

2009

Graphic Design:

Jeffrey Muoz

Production:

Zeidy HidalgoMarianne Fish

Carlos Drews

Ana Fonseca

Edition:

Carlos Drews

Ana Fonseca

Translation:

Lucinda Taft

Cover Photo:Aerial photograph of Playa Grande, Las Baulas National Park, taken on May 1st, 2009 .

Carlos DREWS / WWF

Cite as:

Fonseca, A. & C. Drews. 2009. Rising sea level due to climate change at Playa Grande,

Las Baulas National Park, Costa Rica: inundation simulation based on a high resolution, digital elevation model and

implications for park management. WWF / Stereocarto Report, San Jos, pp. 20.


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Summary

Flooding models under dierent sea-level rise

scenarios are needed to better plan or coastal

development and protected areas, in a way such

that both marine turtles and local communities

beneft. Playa Grande, the most important nest-

ing site o the Eastern Pacifc or the critically

endangered leatherback turtle, is located in Las

Baulas National Park, Costa Rica. It is realisticto expect a 1 m sea-level rise by the end o

the century due to climate change. This would

imply a 50 m retreat o the beach landwards.

Additionally, the high-resolution, digital eleva-

tion model reveals that or the most part the

inundation o the Playa Grande area will occur

rom behind. As sea level rises, the water will

advance through the mouth o the Tamarindo

estuary, and into the surrounding wetlands, in-

undating part o the land bordering the current

mangroves. The uture o Playa Grande depends

on its ability to retreat as sea level rises and

at the same time maintain adequate ecological

conditions or the nesting o leatherbacks. This

implies that existing and uture inrastructure

does not hinder the retreat o the beach and that

the buer zone o the national park warrants e-

ective environmental mitigation measures in

the light o the uture locations o the beach

and o the retreat o the mangroves. The law

proposal to rectiy the boundaries o the park

that would reduce its width to a ringe o 50 m

would imply that the park would be underwater

by the end o the century. The beach would be

located inside the proposed wildlie reuge and

turtles and their nests would compete or space

with houses and other inrastructure. Once the

beach retreats against the inrastructure, the

wave action against roads and buildings will

cause erosion and, consequently, loss o nest-

ing area. In relation to rising sea levels, the pro-

posal to rectiy the boundaries o the national

park is shortsighted and not precautionary. It

would compromise in the mid- and long-term

its ecological role as leatherback nesting area,

and as such, the very reason or the creation o

this particular park. Implementation o adapta-

tion measures to counter the impacts o climatechange in turtle nesting beaches is an interna-

tional commitment under the Inter-American

Convention or Marine Turtle Protection and

Conservation, to which Costa Rica is a signatory

party. With the implementation o such mea-

sures, Costa Rica has the opportunity to main-

tain its regional leadership in the conservation

o marine turtles and its status as a world-class

reerence in biodiversity conservation.

Inundation simulation based on a high

resolution, digital elevation model and

implications for park management

Carlos Drews and Ana Fonseca


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Results and discussion

Simulation o the inundation o Playa Grande

One important preliminary step toward the denition

o adaptation measures or sea level rise and globa

warming due to climate change are accurate loca

inundation models that take the greatest number o

atmospheric, terrestrial and oceanographic variables

into account. Inundation modeling is a complex process that involves several analytical stages o the

marine-coastal and atmospheric dynamic. As a rs

stage, a digital land model was generated using LI-

DAR technology, an aerial sensor that scanned the

beach with laser beams, yielding high-resolution data

on topographical elevation. A possible inundation was

simulated statically based on this topography, ortho

photography and dierent sea level rise scenarios (0

to 150 cm)8. These simulations, images and maps are

useul tools or raising awareness and helping gov

ernmental and civil society decision makers plan the

incorporation o sea level rise into protected area and

coastal development management. The next stage o

this project will gather and add data on wave action

tides, bathymetry, currents, tectonics, precipitation

temperature, and more to the topographic data, to

analyze a wide range o vulnerabilities and generate

a more accurate, dynamic model o beach movemen

and inundation due to the impact o climate change

on these beaches.

According to the most recent estimates o a one-meter sea-

level rise anticipated or the end o the century, the beach

at Playa Grande will retreat some 50 meters during this

period 9, as the beach is pushed landwards by wave actio

as the sea level rises. Under this assumption, Figure 9 rep

resents the landward displacement o the beach, relative to

the current tide line. The public zone o 50 meters and the

maritime-terrestrial zone will gradually shit landwards too

I there were buildings in this zone, in the uture nesting

turtles would compete directly or space with houses and

other inrastructure as the beach shited to surround those

buildings. In theory, this could turn out to be the case with

regards to some o the buildings now in existence (Fig. 10)

although it is unknown whether the nesting zone preerred

by the leatherbacks will include these specic stretches o

8 Modications to the littoral zone during the periodcontemplated in the simulation are not illustrated. This

simulation is also known as a bathtub model o sea leve

rise. It does not take the retreat o the beach as sea leve

rises into account.

9 Source: Daz-Andrade, J.M. 1996,Anlisis de la

vulnerabilidad de la zona costera ante el ascenso de

nivel del mar por un cambio climtico global Costa

del Pacfco de Costa Rica, Inorme fnal del Proyecto

Centroamericano sobre Cambio Climtico, Comit Re

gional de Recursos Hidrulicos. San Jos, Costa Rica

ever, we also discuss the management implications o

projections or beach retreat based on published ac-

counts by other authors. A subsequent stage is expect-

ed to generate a dynamic model o the inundation that

also considers bathymetry, wave action and the littoral

zones response in shape and size. The latter will allow

calculation o eventual reorientations o the beach in the

uture and the range o extreme storm surges.

Methodology

Playa Grande beach is approximately 4.3 km long with

white sand, located in Guanacaste province. Its geo-

graphic coordinates are: northern end 10 20 44 N,

85 51 37 W and southern end 10 18 30 N, 85

50 11 W. The beach is protected within Las Baulas

Marine Park that also includes Ventanas, Langosta and

Carbn beaches, the San Francisco and Tamarindo es-

tuaries, and 125 m landward rom the regular high tide

line. Leatherbacks nest mainly in the center o the beach

where there is very little inrastructure at present.

On June 6, 2009, a fy-over o Playa Grande and Junquil-

lal Beach was done in a Piper Azteca PA-23-250 aircrat,

equipped or fights with simultaneous LIDAR and digital

photography technology. Flight hours or Playa Grande

were 08:04 to 08:16 am and or Junquillal rom 08:21 to

08:28 am, which determines the tide level shown in the

photographs. At the time o the overfight on that day, low

tide was at 7.35 h (46 cm) and high tide was at 13.52 h

(265 cm) in Puntarenas as a point o reerence. Thus, the

photographs portray low tide conditions. During the fight

laser data were captured with a LIDAR Leica ALS 50 II

sensor or generating the Digital Terrain Models (DTM,

see Fig. 4) and Digital Surace Models (DSM) rom the

lowest low tide point to 500 m landward, with a resolution

o 4 to 5 points/meter2 and an altitudinal precision o 15

cm. Additionally, aerial photos were taken on a 1:30,000

scale with a medium ormat RCD 105 digital camera that

were then ortho-rectied (Figs. 3, 5-10). The images

were integrated into a tridimensional vision system called

Stereocaptor to produce animations7 o the possible in-

undation o Playa Grande under dierent sea level rise

scenarios (rom 0 to 150 cm, every 10 cm).

The anticipated 50-m retreat o the beach landward has

not been refected in the simulations o simple inunda-tions. In order to illustrate this retreat, the orthophoto-

graph o the uture scenario in Figure 8 was edited us-

ing Adobe Photoshop, moving the beach landward and

maintaining current building locations as points o reer-

ence. In Figures 9 and 10, lines are used to indicate the

modied boundaries o the beach as a consequence o

their eventual uture displacement.

7 These animations are not included in this report

and are distributed by WWF upon request.

sures. This report graphically presents the results o

simple models to simulate inundation due to sea level

rise at Playa Grande and it mentions the implications

o the expected landward retreat o the beach or the

management o the national park.

Purpose and scope o this study

Massive hotel development and the parceling o real

estate or condominiums are exerting major ecosys-tem pressures in Guanacaste province that are most

intensive on the coastal-marine environments, where

aquiers, wetlands and mangroves are being aected.

The main challenge at Playa Grande is to achieve en-

vironmental compatibility o present and uture coastal

development with the ecological unction o the national

park. Some properties are still held within the park

boundaries and the government as per the correspond-

ing legal ruling should expropriate these. A drat law

has been submitted by the Presidency o the Republic

or the consideration o the Legislative Assembly that

proposes a reduction in the width o the park in order

to exclude these properties rom the area o maximum

protection and avoid the extensive costs o the expro-

priation. WWF has expressed its opposition to this drat

law based on considerations o the implications o sea

level rise, arguments that up until now did not gure

in the debate. Furthermore, a technical document rom

SETENA is in preparation about the park buer zone

(500 m wide, see Fig. 9) that will recommend mitiga-

tion measures or the environmental impact on the park

o development. Construction permits have been para-

lyzed in this zone until the Constitutional Court makes a

ruling on SETENAs recommendations. Consideration o

sea level rise is pertinent in these processes because

this will determine the location and condition o the

beach in the medium and long term.

The purpose o this study is to generate inundation

simulations or some scenarios o sea level rise due to

climate change, which can be used to raise awareness

in coastal communities about this problem and aid the

management authorities o protected wildlands in de-

signing inrastructure-ree setbacks that will allow Las

Baulas National Park to ulll its ecological unction in

the long term. We made a tridimensional, high-reso-

lution digital land model o Playa Grande using LIDAR

technology6

. At this stage the study has been limited togenerating a simple bath tub fooding simulation or

the sea level rise projected or the end o the century,

based on detailed topography o the littoral zone. How-

6 LIDAR (Light Intensity Detection and Ranging):

This is an active laser system that works in the visible,

ultraviolet and near inrared spectrum. It has applica-

tions in studies o the atmosphere and as an altimeter

in overfights that generate very accurate digital eleva-

tion models.


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a periodic record should be made o the distance

rom several points on the beach to xed points on the

coast, such as buildings and boundary markers These

records are necessary or designing the inclusion o set-

backs (zones behind the beach with no inrastructure

in land-use regulatory plans as an adaptation measure

to sea level rise. Las Baulas National Park has still not

designed the setbacks that are technically necessary to

compensate or sea level rise, such that the beach can

retreat landward and continue exercising its unction asthe most important nesting site o the Eastern Pacic o

leatherbacks, a critically endangered species.

The setback zone is essential to maintain the integri

ty o the coastal vegetation strip, which will also shi

arther inland; the vegetation unctions as a natura

barrier or mitigating the eects o articial lighting

rom buildings that disorients the turtles, and also

provides shade that can reduce the probability o

nest overheating13. Furthermore, prudent setbacks

must also be established to allow the gradual retrea

o this parks mangroves without harming their eco

logical unction. National parks should be designed

to ull their protective unction long-term. WWF is

preparing to work in coordination with SINAC and the

authorities o Las Baulas precisely to address this

challenge.

International commitment to adaptation to

climate change

In April 2009, during the 4th Conerence o the Par

ties to the Inter-American Convention or the Protec

tion and Conservation o Sea Turtles held in San Jos

the government o Costa Rica (a signatory nation

proposed resolution CIT-COP4-2009-R5 Adaptatio

o sea turtle habitats to climate change, which was

approved by consensus. This trailblazing resolution

urges signatory nations to design, identiy and imple

ment stronger corrective measures and adaptations

to climate change in management plans, regulatory

plans, and programs or the protection and conserva

tion o sea turtles and their habitats, among others

The implementation o corrective and adaptation mea

sures is an international commitment, in which Costa

Rica is already showing clear leadership with regard to

sea turtles, as demonstrated by the conservation proj

ect at Junquillal Beach where adjustments in management are now being implemented on the beach to

mitigate the impacts o climate change. This kind o

initiative is pending or Las Baulas National Park and

the other Costa Rican nesting beaches o regional and

global importance.

13 Measurements made by WWF at Junquillal Beac

indicate that the coastal vegetation strip can reduce in

cubation temperature by 2-3 degrees Centigrade along

the higher elevation stretch o the beach.

ta Rica, spring tides can reach up to 1 m above the level

o ordinary high tides12. This preliminary fooding simula-

tion does not refect that a 1-meter sea level rise by the

end o the century, considered realistic by the scientic

community, would probably also completely inundate the

50-meter strip o the current public zone. Figure 8 re-

constructs the eventual location o the beach by the end

o the century, displaced some 50 m landward, and it

illustrates how some buildings would be immersed on the

beach (also see Figs. 9 and 10). The estimated 50-me-ter retreat o the beach by the end o the century due to

sea level rise means that the current public zone will be

totally submerged by that time (Fig. 9). The drat law or

rectiying the boundaries o Las Baulas National Park11

(in review by the Permanent Special Commission or the

Environment o the Legislative Assembly) would reduce

the park to this 50-meter strip, condemning it to be under

water in the uture and, thus, to disappear by the end

o the century. In addition will be completely within the

proposed wildlie reuge, in immediate confict or space

with buildings and other inrastructure. Under these con-

ditions, the ecological unction o the beach as a leather-

back-nesting site would be seriously compromised.

Figures 8, 9 and 10 are approximations o the possi-

ble impact o the retreat o the beach due to sea level

rise but this estimate could be made more accurate in

a one-to-two year investigation o Las Baulas National

Park10 that would consider the evolution o wave ac-

tion, winds, tides and the topography under climate

change scenarios in a way that would also refect the

intrusion o peak high tides, to generate a dynamic in-

undation model with probability levels or normal and

extreme events. Inrastructure-ree setbacks must be

designed to reduce the vulnerability o the investments

in coastal development to the fooding due to rising

sea level and so as not to block the ormation o new

beach inland, thus maintaining conditions suitable or

nesting sea turtles. Such setbacks are a undamental

tool in sea turtle conservation, particularly in the con-

text o adaptation to climate change12.

Inrastructure-ree setbacks to compensate

or sea level rise

The Manual sobre tcnicas de manejo y conservacin

de las tortugas marinas en playas de anidacin de Cen-

troamrica, published in 2008 by the Inter-AmericanConvention or the Protection and Conservation o Sea

Turtles, o which Costa Rica is a member, indicates that

11 Expediente No. 17.383, Recticacin de Lmites

del Parque Nacional Marino Las Baulas y Creacin del

Reugio de Vida Silvestre Las Baulas de Propiedad Mixta

12 Fish M.R., I.M. Ct, J.A. Horrocks, B. Mulligan, A.R.

Watkinson and A.P. Jones. 2008. Construction setback

regulations and sea-level rise: mitigating sea turtle nesting

beach loss. Ocean and Coastal Management 51:330-341.

the beach in the uture. However, once the beach reaches

the inrastructure, wave action on roads and/or buildings

will cause erosion and loss o beach area. In Bonaire, or

example, it is estimated that 32% o the beach area will be

lost with a sea level rise o 50 cm, due to the inrastruc-

ture and natural obstacles that would impede the gradual

retreat o the beach10. It is essential that the current size

o Las Baulas National Park is maintained and buer zone

measures are dened to compensate or beach displace-

ment so that the park best ullls its ecological unction inthe short as well as the long term.

According to the preliminary simulation or a 1-meter

sea level rise, it is very probable that a large part o the

inundation o the Playa Grande zone would occur rom

behind, as sea level rises and water advances via the

mouth o the Tamarindo estuary and the surrounding

wetlands, fooding some lands adjacent to the current

mangrove area (Figs. 1, 2, 5 and 6). The small estuary

zone o Ventanas Beach will be signicantly inundated,

making the road parallel to the beach and the buildings

in this sector highly vulnerable (Figs. 7 and 10).

A quantitative assessment o the current tectonic ten-

dency in the area is still pending, in order to estimate

the component o sea-level rise due to the subsidence

o the continental platorm. The west coast o the Nicoya

peninsula, on which Playa Grande is located, is subsid-

ing. Observations in Junquillal beach suggest, that in

act, the mean sea level is rising along this stretch o

the coast. It is evident that the ocial landmarks o the

public zone need to be relocated inland, since their dis-

tance to the ordinary high tide line is noticeably less

than 50 meters. The tendency o the relative sea level

in Puntarenas or the period 1941-1978 is a net rise,

with a total increment o 51 mm over that period . The

current high tide level (usually drawn and dened as the

boundary between the maritime and terrestrial domains

or cartographic and legal purposes) is inundated ap-

proximately 8% o the time. However, i average sea

level rises by 1 m, this value increases to 51%, which is

the percentage o inundated time currently correspond-

ing to the mean tide level (mean between the average

low and the average high tide). Unortunately, there is

lack o data series or changes in sea level along the

Pacic littoral o Costa Rica, which have the continuity

and duration needed to estimate with more precision

these tendencies or several locations along the coast(A. Gutirrez, personal communication).

Sea level rise is a gradual process. Extreme tidal action

will increasingly reach those areas that today seem sae

rom inundation. Along the northern Pacic coast o Cos-

10 Fish, M.R., I.M. Cote, J.A. Gill, A.P. Jones, S.

Rensho and A.R. Watkinson. 2005. Predicting the

impact o sea-level rise on Caribbean sea turtle nest-

ing habitat. Conservation Biology 19:482-91.


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Figure 1. Inclined orthophotograph o Playa Grande

illustrating the inundation area corresponding to a 1-meter

sea level rise, probable by the end o the century.

Figure 2.DTM image o Playa Grande topographyillustrating dierences in elevation details in relie with

15-cm vertical resolution and the inundation area

corresponding to 50-cm and 100-cm sea level rises.

Conclusion

Flooding models are needed or dierent sea level rise

scenarios in order to better plan or coastal develop-

ment, in a way that would benet both sea turtles and

local residents. This project aims to contribute case

studies to enhance knowledge o the coastal process-

es associated with climate change on beaches o the

tropical Eastern Pacic that will allow better manage-

ment o the challenges o erosion, territorial manage-ment, conservation o marine-coastal biodiversity and

responsible development. The uture o Playa Grande

beach depends on its capacity to retreat rom rising

sea levels while maintaining ideal ecological condi-

tions or leatherback nesting. This implies that existing

and uture inrastructure must not block this retreat

and that the buer zone o the national park ensures

eective environmental mitigation measures or the

uture landward location o the beach. Due to the ore-

cast retreat o the beach, a rectication o the park

boundaries that would reduce its current width and

allow continued development o inrastructure withinthe 125-meter strip above the current regular high

tide level is neither a precautionary nor a preventa-

tive measure and it would compromise in the medium

and long term its ecological unction as a leatherbac

nesting site, the very reason or which this protected

area was declared. The implementation o adaptatio

measures or climate change on nesting beaches is

an international commitment under the Inter-Ameri

can Convention or the Protection and Conservation o

Sea Turtles, to which Costa Rica is a signatory party

In implementing such measures, Costa Rica has the

opportunity to maintain its regional leadership in seaturtle conservation and as a global reerence in biodi

versity conservation.

Figures

Year 2009

Year 2009 + 50 cm + 100 cm

+ 100 cm

Source:WWF/Stereocarto

So

urce:WWF/Stereocarto

Source: WWF / Stereocarto


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Figure 3. Inclined orthophotograph o Playa Grande, taken

on June 6, 2009.

Figure 4. DTM image o Playa Grande topography

illustrating details o dierences in elevation in relie with

15-cm vertical resolution. Note the low elevation o the

mangrove zone around the Tamarindo estuary and the

estuary behind Ventanas Beach. The beach dune stands

out with an elevation a little higher than the landward

terrain behind it.


Source:W

WF/Stereocarto

Actual sea level


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Figure 5. Comparison o vertical image orthophotographs o the eastern sector o Playa Grande illustrating current

sea level (above) and the inundation area with a 100-cm sea level rise, estimated or the end o the century. This

image does not include the expected 50-m displacement o the beach landward (see Fig. 9).

Source:WWF/

Stereocarto



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Figure 7. Comparison o vertical image orthophotographs o Ventanas Beach, western sector o Playa Grande, illustrating current sea level (above) and the inundation area

with a 100-cm sea level rise, estimated or the end o the century (below). This image does not include the expected 50-m displacement o the beach landward (see Fig. 10).




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Figure 8. Comparison o vertical orthophotographs o Playa Grande illustrating current sea level (above) and a 100-cm sea level rise, estimated or the end o the

century (below). This image recreates the expected 50-m displacement o the beach landward in response to sea level rise. Some buildings would end up on the

beach, subject to the impact o storm surges. Note that the road parallel to Ventanas Beach is highly vulnerable to eventual erosion, as it is situated on a narrow

sand bank, lanked by water on both sides and exposed to the beating o the waves and storm surges (let side o the image).


Source:WWF/Ste

reocarto


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Figure 9. Vertical orthophotograph o Playa Grande, illustrating areas o Las Baulas National Park in this sector, as well as the expected landward

displacement zone o the beach o 50 m in response to sea level rise, estimated using the Bruun rule (see the text).


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Figure 10. Vertical orthophotograph o Playa Grande and Ventanas Beach, illustrating areas o Las Baulas National Park in the northwestern sector, as

well as the expected landward displacement zone o the beach o 50 m in response to sea level rise, estimated using the Bruun rule (see the text).


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Documents

Rising Sea Level Due to Climate Change in Playa Grande, Las Baulas National Park, Costa Rica - Drews & Fonseca 2009