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Irrigated agricultural ecosystems in Africa
Timothy O. WilliamsDirector, Africa
International Water Management Institute (IWMI)
WLE/IWMI Workshop on Unlocking Value fromPublic Large Scale Irrigation Systems, Negombo, Sri Lanka, 7/4/2015
Presentation Outline
• Introduction
• Review of ecosystem impacts of irrigation
• New drivers of irrigation – opportunities & challenges
• Researchable priorities in ecosystem-inclusive management of irrigation in Africa
Introduction
• Irrigated agriculture, an ecosystem management activity.
• Mosaic of irrigation systems in Africa.
• Diverse irrigated agroecosystems with great variability within and between systems.
Introduction (continued)• Irrigation has been promoted primarily
to meet food security and economic development objectives, with ecosystem concerns considered secondary.
• Poor understanding of linked social-ecological systems that irrigated agroecosystems represent.
• Short-term perspectives of decision makers.
Basin
Irrigation potential (‘000 ha)
Environmental impact hazard
Salinity Health Forest Fishery Wildlife
Senegal River 420 +++ ++ + + +
Niger River 2,817 +++ ++ + ++ ++
Lake Chad 1,163 +++ ++ + ++ ++
Nile River 8,000 +++ + + + ++
Congo/Zaire River
9,800 + + ++ + +
Zambezi River 3,160 ++ ++ + + +
Okavango 208 ++ + + + +++
Limpopo River 295 ++ ++ + + +
Mediterranean Coast
850 +++ + + + +
Environmental impact assessment of irrigation by basin in Africa
Source: FAO, 1997. +++ serious; ++ moderate; + low or nil
Impact category Wonji/Shoa, Ethiopia Finchaa Valley, Ethiopia
Senegal River
Quality of irrigation water
Good, with no risk for irrigation purposes
Good, with no risk for irrigation purposes
Saline water
Hydrology Rising of groundwater table
High surface runoff Sea water intrusion
Change in soil properties
Damage to soil structure and soil crusting
Soil degradation due to sediment deposits from hills
Soils exposed to increasing salinity
Downstream water quality
Affected adversely by agrochemicals used in irrigated agriculture
Affected adversely by agrochemicals used in irrigated agriculture
Increase in water table salinity
Surrounding ecosystems
n.a. Natural vegetation cleared
Proliferation of aquatic weeds; reduced flooding and dikes for irrigation have reduced traditional grazing land
Environmental impact analysis of large-scale irrigation schemes in Ethiopia and Senegal River
Sources: D. Ruffeis et al. (2008); DeGeorges and Reilly, 2006; Dumas et al. (2010)
Impact category Wonji/Shoa, Ethiopia Finchaa Valley, Ethiopia
Senegal River
Quality of irrigation water
Good, with no risk for irrigation purposes
Good, with no risk for irrigation purposes
Saline water
Hydrology Rising of groundwater table
High surface runoff Sea water intrusion
Change in soil properties
Damage to soil structure and soil crusting
Soil degradation due to Soils exposed to increasing salinity
Downstream water quality
Affected adversely by agrochemicals used in irrigated agriculture
Affected adversely by agrochemicals used in irrigated agriculture
Increase in water table salinity
Surrounding ecosystems
n.a. Natural vegetation cleared
Proliferation of aquatic weeds; reduced flooding and dikes for irrigation have reduced traditional grazing land
Environmental impact analysis of large-scale irrigation schemes in Ethiopia and Senegal River
Sources: D. Ruffeis et al. (2008); DeGeorges and Reilly, 2006; Dumas et al. (2010)
Potential environmental impacts of SSISs
• Excessive groundwater extraction leading to land subsidence.
• Gully erosion and desiccation of dambos/fadamas, particularly in intensively utilized dambos in dry areas e.g. Kano Basin in Northern Nigeria and the communal lands in Zimbabwe.
Summary of ecosystem impacts of irrigation in Africa
• Lack of detailed studies and baseline data to rigorously assess ecosystem services associated with irrigation and impacts of irrigation on surrounding ecosystems.
• There is evidence that irrigated agriculture, particularly LSISs, have led to adverse impacts on surrounding ecosystems.
• The confounding effects of natural or other anthropogenic stressors are not often evaluated.
Summary of ecosystem impacts of irrigation in Africa (continued)
• Detailed analysis of impacts of SSISs on ecosystems and ecosystem services still lacking.
• Is there an irrigation scale effect on ecosystem services provided and impact on surrounding ecosystems?
A resurgence of interest in irrigation in Africa
• A World Bank (WB) initiative to increase the area under irrigation in 6 Sahelian countries from the current 400,000 ha to 1million ha by 2020 at a cost of $7 billion • A WB loan of $400 million to revitalize LSIS and transform irrigation management in Nigeria • New private sector commercial LS and MSISs in Ghana, Nigeria, Tanzania and Zambia
A resurgence of interest in irrigation in Africa
Why? Why now?
What are the new drivers, opportunitiesand challenges?
Source: FAO, 2014
Research questions • What are the basic incentives and disincentives for ecosystem-based management of irrigation? • What are the challenges of ecosystem-based management of irrigation for long-term food security, poverty alleviation and economic development?
• What practical and politically feasible policies and strategies are needed to enable transition towards ecosystem-based management of irrigation?
Research will be needed to:
• Improve knowledge of the whole range of ecosystem services associated with irrigation –their values and costs.
• Determine and differentiate the impacts of other natural and anthropogenic stressors from the impact of irrigation.
Research will be needed to:
• Identify economic instruments and innovative financing mechanisms that can allow the application of ecosystem-based irrigation management.
• Monitor long-term changes in irrigated agricultural ecosystems from a basin perspective.
Thank you for your attention
