Cn 2 th14_inida_assessment of land degradation_baptista


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Cn 2 th14_inida_assessment of land degradation_baptista

  1. 1. Assessment of land degradation indicators in an insular sahelian mountain region – case study of the“Ribeira Seca” watershed J. Tavares; I. Baptista; A.Ferreira; L.Varela; J. Bentub and COA Coelho
  2. 2. Content • Introduction (background and justification and objectives) • Country data • Factors contributing to land degradation • Soil and water conservation techniques • Materials and method – The study site – Methodology • Results and discussion • Conclusion
  3. 3. Introduction • Cape Verde, as a sahelian country, has been severely affected by the desertification phenomenon, although extreme efforts are being made to reverse the process • Desertification is a major issue in Cape Verde and directly influences the livelihoods of local farmers • Several techniques were implemented throughout the last decades to halt the desertification process – Efficiency has hardly been accessed.
  4. 4. Introduction • To combat desertification, integrated approaches are to be sought, combining social and biophysical viewpoints, and linking local and scientific knowledge • The first step is to assess the problem using an integrated approach, to identify variability and worst cases, as basis of strategy and actions to be defined • Indicators are very useful in this context
  5. 5. Indicators • Environmental and socio-economic indicators play an increasingly important role in supporting development policies for combating desertification • An indicator is a measurement that reflects the status of social, economic or environmental systems • They can be used to track changes in complex systems and monitor progress towards pre- determined goals • Their role is to simplify the complex interrelations of the socio-economic and environmental reality and convey them in an unambiguous way
  6. 6. Some country data • Location: West African coast • Surface area: 4033 km2 • Composed of 10 islands and 5 islets • Population: 430 000 • Arable land: 10% of total land area (42000 ha) • Dryland agriculture: 38 000 ha (>90%) • Irrigated land: 3000-5000 ha (<5.0%) • Climate: dry tropical w/2 distinct seasons: dry season (November to June) and the rainy season (July to October) • Mean annual rainfall: 230 mm with great spatial-temporal variability • Terrain: steep, rugged, rocky and volcanic • Contribution of agriculture to GDP: 12 %
  7. 7. Objectives • Goal: To improve the knowledge on desertification risks related with land use • Specific objectives: 1. assess the indicators applied in the various land use type 2. analyze the main drivers of desertification and their impact on social, economic, natural capital, ecological and economic functions
  8. 8. Factors contributing to land degradation • Heavy rainfall events ⇒ Flash floods (Soil erosion by water) • Low, insufficient and irregular rainfall (space and time) • Frequent droughts • Soil fertility decline (no nutrient replenishment) • Low soil OM content • Cultivation of very steep slopes • Inadequate rain-fed farming practices • Overexploitation of ground water ⇒ Water and soil salinization Land degradation and desertification
  9. 9. Soil and water conservation techniques • To deal with land degradation (erosion and drought), CV governments have implemented several SWC techniques – in field (mechanical and biological structures) • Terraces, stone walls, contour ridges • Vegetation live barriers (green belts) – off field • water harvesting (large dams, reservoirs, etc) • check dams, etc.)
  10. 10. Contour ridges combined with leucaena leucocephala Contour stone wall combined w/ agroforestry species Contour stone walls combined w/ Furcraea gigantean Stone walls combined with aloe vera
  11. 11. • Contour stone walls in corn/bean production system (left) • Terraces built on slope, planted with rainfed crops - corn & beans (right)
  12. 12. Contour ridges on very steep slope for peanut production in-field (contour stone wall w/ vegetation barrier) and off-field (check dams) SWC techniques contour stone wall Aloe vera barriers
  13. 13. Off-field SWC techniques Gabion check damsMasonry check dam
  14. 14. Water harvesting Large Dam construction for rain water retention (Poilão Dam) Large Reservoir (São Jorge)
  15. 15. Materials and Methods
  16. 16. Study site characteristics • Location: East-central side of the Santiago island • Population: 14 343 • Main activity: agriculture • Drainage area: 71.50km2 • Land use: 83% rainfed agriculture; 5 % irrigated land; 4% forest; 1% rock outcrop; 7% other • 4 bioclimatic zones: 11% humid; 20% sub humid; 49% semiarid; 20% arid • Main dryland crops: maize and beans • Irrigated crops: banana, sugarcane, roots and tubers and vegetables • Average slope: 8.6%
  17. 17. The study site: Physiographic indices Sub basin / basin Area Length river Alt. max Alt. min Gravelius Index (Kc) Shape form (Kf) River slope Basin slope Km2 Km m m - - % % Longueira 4,18 3,45 1126 239 1,31 0,35 26 33,0 Grande 4,86 4,98 750 130 1,33 0,20 12,4 15,9 Godim 5,01 5,30 570 145 1,37 0,20 8,5 24,0 Seca 24,94 18,0 642 0 2,47 0,07 7,2 6,3 Ribeira Seca 71,50 18 1394 0 1,31 0,22 7,20 8,60
  18. 18. Methodology • 103 points were surveyed in the watershed following WB2 methodology • The indicators used are based in the DPSIR framework • Classes were assigned using existing classification systems such as the European geo- referenced soil data base, or existing research data • The various classes of indicators were organized according to the importance to land degradation and desertification risk DRIVER S Efficiency/Descr iptive Indicators Performance Indicators RESPONSES Risk Assessment PRESSURES Descriptive Indicators STATE IMPACTS Descriptive Indicators DPSIR elements and related indicators
  19. 19. Flow chart of the process
  20. 20. Results and Discussion
  21. 21. Physiographic characteristics
  22. 22. Desertification risk
  23. 23. Mitigation techniques
  24. 24. Desertification risk map • Almost 90 % of the study area is sensitive to desertification • This situation reflects the particular geo- morphological characteristics of the watershed: low lands, high population density, and lack of soil cover
  25. 25. Conclusion • The indicators used to assess the desertification risk at the Ribeira Seca catchment revealed to be a very practical and useful tool: – Allowing direct comparison between different realities, rank the desertification risk, – Identifying the more detrimental practices and – Pinpointing the locations at higher risk of desertification • They allow perception of different realities within a same area, and to evaluate the performance of different conservation strategies, practices and techniques.
  26. 26. Thank you for your attention and inputs