V&A Studies on coastal zones: the case of Senegal

3 june 2002 AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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V&A Studies on coastal zones: the case of Senegal

Dr Isabelle NIANG-DIOPDepartment of Geology, Faculty of Science and

TechnologyUniversity Cheikh Anta Diop, Dakar (SENEGAL)

[email protected]


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The Senegal example

Two studies realized (1991 and 1999)

Conditions Results (for a sea level rise of 1 m

by 2100) What to deduce ?


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Conditions

First study Study in

collaboration with USA

All the Senegalese coastline

EPA funding (17,391 – 26,087 US$ )

10 months (may 90 – february 91)

Video recording (AVVA)

Second study Pluridisciplinary

team (11 experts) Case studies : Cap

Vert and Saloum Netherlands funding

(86,000 US$ ) 2 years (97-99) Remote sensing

and GIS


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Methodologies used The Common Methodology (IPCC, 1991),

basis for the IPCC methodology (Carter et al., 1994). The seven steps methodology

Based on scenarios Climate change scenarios

Sea level rise scenarios (used in the 2 studies) Inundation levels Other climate parameters (temperature,

precipitations,..) Socio-economic scenarios

Population growth Economic growth


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Sea level rise scenarios

Sr, t = Sg, t + So, t + V. t

avec Sr, t : relative sea level rise in t years

Sg, t : global mean sea level rise in t

So, t : regional changes in sea level due to oceanic circulation (currents, …)

V : earth movements (m/year) t : number of years considered


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Sea level rise with the SRES

See IPCC Third Assessment Report (2001)


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Inundation levels (Hoozemans et al., 1993)

D = MHW + Sf + Wf + Pf

MHW mean high water levelSf sea level rise

Wf heigth of storm waves of a givenreturn period

Pf rise in sea level due to barometric pressure


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Socio-economic scenario

the discount rate

Controversial question (utilitity, rate)

Multiplicator factorDt = 1 / (1 + r)t

Dt is discount factor in year t and r the discount rate used (2 to 7%)


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Scenarios generation Climate change scenarios

See the training workshop CC scenarios generators (MAGICC-

SCENGEN, regional CC models) Downscaling, national CC scenarios

Socio-economic scenarios National scenarios (to be preferred) United Nations and others scenarios (WB,

UNDP, WRI,…)


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Scenarios used First study

Climate change scenario Sea level rise by year 2100 : 0.2; 0.5; 1 and 2

m Inundation levels

2m1m

0.5m

No socio economic scenario


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Scenarios used Second study

Climate change scenario Sea level rise

2050 : 7, 20, 39 cm 2100 : 20, 49, 86 cm

Inundation levelsThe minimum inundation level by 2100 is calculated for minima values of themean high sea level, mean swell heights and the low estimation of sea level rise.The maximum inundation level considers mean values of the mean high sealevel, storm waves with a 1/100 return period and the high estimation of sea

level rise. Coast north of Dakar : 2 and 8 m Coast south of Dakar and Saloum : 2 and 6m

Other parameters Temperature rise : 1° and 1.9°C by 2050 Precipitation decrease : -1 to –10% in Cape Verde ; -1 to

–15% in Saloum


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Scenarios used Second study

Socio-economic scenario Population growth

Cap Vert : 2.99% Saloum : 2%

Agricultural production growth rateO.41%

Discount rates3 and 6%


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Impacts assessment Biophysical impacts

Land losses due to Coastal erosion Inundation

Salt water intrusion in coastal aquifers Coastal ecosystems Halieutic resources and fisheries


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Impacts assessment Socio-economic impacts

Population at risk Economic value at risk

Buildings Infrastructures Agricultural production


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Coastal erosion induced by SLR

The Bruun rule (1962)

A simple rule but based on a number of assumptions (equilibrium profile)

R = G L s (B + d)

R is the coastal retreat, L the width of the active profile, B the dune heigth, d the depth of closure, s the sea level rise and G a overfill ratio


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The Bruun rule (1962)

Bs

d

L

R

Profile translation


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Coastal inundationIn the second study Inundation levels considered as contour

levels. Digitalization of contour levels Satellite images transformed and land-

use maps Use of a GIS : combination of the two

types of information Generation of areas and types of

inundated coastal zones


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Other biophysical impacts (1)

Salt water intrusion in the coastal aquifers the Ghyben-Herzberg formula : determine the

depth and distance to the coast of the interface sea water / freshwater (see UNEP guidelines)

the FEFLOW model was calibrated and used to determine the evolution of the salt water intrusion in the Dakar aquifer (Faye et al., 2001)

Coastal ecosystems (expert judgement) « niayes » ecosystem : based on the comparison

with historical data Mangroves : analogue study


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Other biophysical impacts (2)

Halieutic resources (expert judgement) Marine resources

Diminution in the intensity of upwellings and surface waters warming

Modification in coastal habitats (mangroves) Estuarine resources

Increase of salinity Increase of the dynamics Disparition of mangroves


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Socio-economic impacts

First study Based on the video recording and

analysis of buildings Types of buildings with value attribution

economic value at risk Rate of occupancy : 1O people in 100

m2population at risk


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Socio-economic impacts Second study

Based on the analysis of inundated areas Population density by zones and growth rate

population at risk Density of inhabitants by house (7.5 in Dakar and

9.6 in the Saloum estuary) habitat at risk Capital and added value by hectare Industrial

value at risk (only for the Mbao industrial zones) Road lengths and types identified, value per km

and type applied road infrastructures at risk area of agricultural production multiplied by

yields and a growth rate agricultural production at risk


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Adaptation assessment

First study Two options considered:

Protection of important areas Total protection (coasts with10 inhabitant per

km2) Two types of protection options

Seawalls : unit costs For a 0.5 m SLR : 0.12 to 2 million US$ per km For a 1 m SLR : 0.33 to 2.30 million US$ per km

Beach nourishment : unit costs : 6 US$ per m3 plus costs of terminal groins


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Adaptation assessment

Second study Protection option

Coastal protection works (seawalls and groins)

Seawalls: 2.2 to 4.6 million US$ per km Dune fixation : unit costs per ha

Other types of measures


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Vulnerability assessmentvulnerability classes (Nicholls,

1995)Categories of impacts Vulnerability classes

Low Middle High Critical

Populations at risk (in % of total population) Economic value at risk (in % of GDP) Land losses (in % of total area) Loss of wetlands (in % of total area) Costs of protection/adaptation (in % of GDP)

< 1%

< 1%

< 3%

< 3%

< 0,05%

1 – 10%

1 – 3%

3 – 10%

3 – 10%

0,05–0,25%

10 – 50%

3 – 10%

10 – 30%

10 – 30%

0,25 - 1%

> 50%

> 10%

> 30%

> 30%

> 1%


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Results of the first study(for a 1 m SLR)

Land losses - Inundation - Erosion

5,987 km2

55 – 86 km2

Population at risk 112 000 –183 0001.4 – 2.3 % 1990

population

Economic value at risk 499 – 707 millions US$12 – 17 % PNB 1990

Protection costs (important zones)

255 – 845 millions US$


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Results of the second study(for a 1 m SLR)

Cap Vert(1597 km2)

Saloum(4309 km2)

Land losses - Inundation - Erosion

57 – 398 km2

2.9 – 4 km2

1,690 – 2,911 km2

0.8 – 4 km2

Population at risk (in 2100)

730,249 - 4,787,828

847,191 to 11,807,410

Economic value at risk (with a 3% DR)

4.4 – 29.7 milliards $

4 – 55.3 milliards $

Protection costs (with a 3% DR) 0,004 – 0,026 M$ 0.06 M$


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Mangrove estuaries


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Comparison of the 2 studies(for a 1 m sea level rise)

1st study : Sénégal

2nd study: Saloum

Land losses by:InundationCoastal erosion

5,987 km2

55 – 86 km2

1,690 – 2,911 km2

0.8 – 4 km2

Population at risk

112,000 –183, 000 847,191 -11,807,410

Economic value at risk

0.5 – 0.7 milliard US$

4 – 55.3 milliards $

Protection costs 0.3 – 0.8 milliards$

0.06 milliard$


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Results of the second study

1. Other impacts

Lowering of piezometric levels and salinization of numerous coastal aquifers

Risks of disparition of the guinean vegetation typical together with apparition of halophyte species in the « niayes » and modifications of mangrove. The risks are less till a 0.5 m SLR

Diminution of the halieutic production and of landings. Changes in the species composition. Health problems, conflicts, employment


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Results of the second study 2. Other adaptation options

Need for ICZM Better management of coastal and

marine resources (water, halieutic and estuarine resources, ecosystems)

New institutional, legislative measures Promotion of technical measures

(recuperation of salted soils, creation of a CC research center)

No quantification of these measures


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The example of Sénégal : conclusions

Don’t expect to have more than you invest Big differences in the results depending on

the methods used specially for population and economic value at risk

Confirmation of the high vulnerability of the country (south coast and estuaries in particular)

Importance of monitoring, sustainable management of resources, …

But how to take these issues in the development agenda of the country?


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The example of Sénégal : conclusions

It is not finished! New scenarios, models are coming Still limitations in the studies : biophysical

impacts to be quantified, economic valuation of mangroves, consideration of other sectors

And how to take these adaptation options in the development agenda of the country?


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THANK YOU !

Documents

V&A Studies on coastal zones: the case of Senegal