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

V&A Studies on coastal zones: the case of Senegal. Dr Isabelle NIANG-DIOP Department of Geology, Faculty of Science and Technology University Cheikh Anta Diop, Dakar (SENEGAL) isabelle@enda.sn. The Senegal example. Two studies realized (1991 and 1999) Conditions

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

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  1. V&A Studies on coastal zones: the case of Senegal Dr Isabelle NIANG-DIOP Department of Geology, Faculty of Science and Technology University Cheikh Anta Diop, Dakar (SENEGAL) isabelle@enda.sn AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  2. The Senegal example • Two studies realized (1991 and 1999) • Conditions • Results (for a sea level rise of 1 m by 2100) • What to deduce ? AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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

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

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

  6. Sea level rise with the SRES See IPCC Third Assessment Report (2001) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  7. Inundation levels (Hoozemans et al., 1993) D = MHW + Sf + Wf + Pf MHW mean high water level Sf sea level rise Wf heigth of storm waves of a given return period Pf rise in sea level due to barometric pressure AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  8. Socio-economic scenariothe discount rate • Controversial question (utilitity, rate) • Multiplicator factor Dt= 1 / (1 + r)t Dt is discount factor in year t and r the discount rate used (2 to 7%) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  9. 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,…) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  10. First study Climate change scenario Sea level rise by year 2100 : 0.2; 0.5; 1 and 2 m Inundation levels Scenarios used 2m 1m 0.5m • No socio economic scenario AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  11. Second study Climate change scenario Sea level rise 2050 : 7, 20, 39 cm 2100 : 20, 49, 86 cm Inundation levels The minimum inundation level by 2100 is calculated for minima values of the mean 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 sea level, 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 Scenarios used AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  12. Second study Socio-economic scenario Population growth Cap Vert : 2.99% Saloum : 2% Agricultural production growth rate O.41% Discount rates 3 and 6% Scenarios used AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  13. Impacts assessment • Biophysical impacts • Land losses due to • Coastal erosion • Inundation • Salt water intrusion in coastal aquifers • Coastal ecosystems • Halieutic resources and fisheries AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  14. Impacts assessment • Socio-economic impacts • Population at risk • Economic value at risk • Buildings • Infrastructures • Agricultural production AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  15. Coastal erosion induced by SLRThe 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 AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  16. The Bruun rule (1962) R L B s d Profile translation AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  17. Coastal inundation In 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 AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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

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

  20. 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 m2 population at risk AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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

  22. Adaptation assessment First study • Two options considered: • Protection of important areas • Total protection (coasts with10 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 AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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

  24. 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% Vulnerability assessmentvulnerability classes (Nicholls, 1995) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  25. Results of the first study(for a 1 m SLR) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  26. Results of the second study(for a 1 m SLR) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  27. Mangrove estuaries AIACC V&A Training Workshop, Trieste, 3-14 june 2002

  28. Comparison of the 2 studies(for a 1 m sea level rise) AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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

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

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

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

  33. THANK YOU ! AIACC V&A Training Workshop, Trieste, 3-14 june 2002

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