Irrigated agricultural ecosystems in Africa
Timothy O. Williams
Director, Africa
International Water Management Institute (IWMI)
WLE/IWMI Workshop on Unlocking Value from
Public 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.
Environmental impact assessment of irrigation by basin in Africa
Irrigation
potential
(‘000 ha)
420
Salinity
Health
Forest
Fishery
Wildlife
+++
++
+
+
+
Niger River
2,817
+++
++
+
++
++
Lake Chad
1,163
+++
++
+
++
++
Nile River
8,000
+++
+
+
+
++
Congo/Zaire
River
Zambezi River
9,800
+
+
++
+
+
3,160
++
++
+
+
+
Okavango
208
++
+
+
+
+++
Limpopo River
295
++
++
+
+
+
Mediterranean
Coast
850
+++
+
+
+
+
Basin
Senegal River
Environmental impact hazard
Source: FAO, 1997. +++ serious; ++ moderate; + low or nil
Environmental impact analysis of large-scale irrigation schemes in Ethiopia and
Senegal River
Impact category
Wonji/Shoa, Ethiopia
Quality of irrigation
water
Good, with no risk for
irrigation purposes
Hydrology
Change in soil
properties
Downstream water
quality
Surrounding
ecosystems
Finchaa Valley,
Ethiopia
Good, with no risk for
irrigation purposes
Senegal River
Rising of groundwater
table
Damage to soil
structure and soil
crusting
Affected adversely by
agrochemicals used in
irrigated agriculture
High surface runoff
Sea water intrusion
Soil degradation due to
sediment deposits
from hills
Affected adversely by
agrochemicals used in
irrigated agriculture
Soils exposed to
increasing salinity
n.a.
Natural vegetation
cleared
Proliferation of aquatic
weeds; reduced
flooding and dikes for
irrigation have reduced
traditional grazing land
Saline water
Increase in water table
salinity
Sources: D. Ruffeis et al. (2008); DeGeorges and Reilly, 2006; Dumas et al. (2010)
Environmental impact analysis of large-scale irrigation schemes in Ethiopia and
Senegal River
Impact category
Wonji/Shoa, Ethiopia
Quality of irrigation
water
Good, with no risk for
irrigation purposes
Hydrology
Change in soil
properties
Downstream water
quality
Surrounding
ecosystems
Finchaa Valley,
Ethiopia
Good, with no risk for
irrigation purposes
Senegal River
Rising of groundwater
table
Damage to soil
structure and soil
crusting
Affected adversely by
agrochemicals used in
irrigated agriculture
High surface runoff
Sea water intrusion
Affected adversely by
agrochemicals used in
irrigated agriculture
Increase in water table
salinity
n.a.
Natural vegetation
cleared
Proliferation of aquatic
weeds; reduced
flooding and dikes for
irrigation have reduced
traditional grazing land
Saline water
Soil degradation due to Soils exposed to
increasing salinity
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, opportunities
and challenges?
9.5 billion people by 2050
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