3. Assess Environmental and Socio-economic Impacts
Irrigation and drainage projects invariably result in many far-reaching environmental and socio-economic changes. Some of these benefit human population, while others threaten the long- term productivity of the irrigation and drainage projects themselves as well as the natural resource base. Negative changes are not limited to increasing pollution or loss of habitat for native plants and animals; they cover the entire range of environmental components, such as soil, water, air, energy, and the socio-economic system.
Irrigation and the Environment
Irrigation makes possible the expansion and intensification of agriculture. Yet, without appropriate management, irrigation development can have significant negative environmental impacts.
At basin level, irrigation schemes can negatively affect the hydrology. Large irrigation projects which store or divert river water have the potential to cause major environmental disturbances, resulting from changes in the hydrology and limnology of river basins. Reducing the river flow changes flood plain land use and ecology and can cause salt water intrusion in the river and into the groundwater of adjacent lands. Diversion of water through irrigation further reduces the water supply for downstream users, including municipalities, industries and agriculture. A reduction in river base flow also decreases the dilution of municipal and industrial wastes added downstream, posing pollution and health hazards.
Groundwater irrigation can increase the risk of over-abstraction, resulting in groundwater depletion, land subsidence, decreased water quality, and saltwater intrusion in coastal areas.
Moreover, it is important to understand how water quality is affected through irrigation development. The quality of water entering the irrigation area is influenced by upstream land uses, particularly when it comes to the sediment content (for example from agriculture-induced erosion) and chemical composition (for example from agricultural and industrial pollutants). The use of river water with a large sediment load may result in canal clogging. Polluted return flows, containing harmful concentrations of salts, organic wastes, agrochemical residues or other substances, lead to the degradation of downstream ecosystems. Increased nutrient levels in the irrigation and drainage water can result in algal blooms, proliferation of aquatic weeds, and eutrophication in irrigation canals and downstream waterways.
At field level, there is a great risk of waterlogging and salinization. Irrigation-induced salinity can arise as a result of the use of saline water, irrigation of saline soils, and rising levels of saline groundwater combined with inadequate leaching. Salinity reduces plant growth and soil productivity. Salt-affected soils are more fragile and prone to erosion. In the case of sodic soils, the loss of organic matter leads to weakened soil structures, increased carbon dioxide emissions, and decreases water infiltration due to surface sealing. This inevitably affects agricultural productivity, yields, and farmers’ incomes.
Irrigated lands, especially areas with high water tables, typically require drainage to avoid waterlogging. Because groundwater drainage is a complex and expensive operation (often more expensive than the initial development of irrigation itself), there is a temptation to start new irrigation projects while ignoring the need for drainage or delaying its installation until it is urgently needed. However, by the time the need for drainage becomes inescapable, the cost of implementing it may be prohibitive.
Monitoring water tables by means of observation wells (piezometers) as well as groundwater quality is crucial. This can provide an early warning of the danger of salinization and groundwater depletion.
Table 1: Potential negative impacts of irrigation schemes
| Increased evaporation in the scheme
| Degradation of irrigated land
- Increased groundwater recharge, waterlogging and drainage problems
- Soil acidification
- Soil compaction
- Soil erosion
| Poor water quality
- Reduction in irrigation water quality and leaching
- Water quality problems for downstream users caused by irrigation return flow quality
| Groundwater depletion
- Drying up of drinking and irrigation wells
- Saltwater intrusion along coasts
- Reduced base flow
| Reduced downstream river discharge
| Ecological degradation
- Reduced biodiversity in irrigated and surrounding area
- Damage to downstream ecosystems due to reduced water quantity and quality
| Negative impacts on human health
- Increased incidence of water-related diseases
Can Solar-powered Irrigation Help Improve Water Use Efficiency?
The introduction of solar technology can be coupled with more water efficient irrigation methods that can help improve the water application efficiency in the field. Nevertheless, there is a risk that instead of saving water, this may actually lead to increased water consumption in situations where no barrier exists to encourage or incentivize efficient water use. Farmers may (i) apply more water in the field overall (for example, when shifting from deficit to optimal irrigation), (ii) expand the area of land under irrigation, (iii) shift to higher value, but often more water-intensive crops, (iv) sell water to neighbouring farmers and communities. This is particularly an issue in areas where groundwater resources are already overexploited and recharge rates are slow.
It may be important to distinguish between the following concepts:
Water Use Efficiency represents the ratio between effective water use and actual water withdrawal. It characterizes, in a specific process, how effective the use of water is. Efficiency is scale and process dependent.
Irrigation Efficiency: The ratio or percentage of the irrigation water requirements of crops on an irrigated farm, field or project to the water diverted from the source of supply.
Scheme Irrigation Efficiency: The scheme irrigation efficiency (in %) refers to the water pumped or diverted through the scheme inlet, which is effectively consumed by the plants.
The scheme irrigation efficiency can be sub-divided into:
- The conveyance efficiency, which represents the efficiency of water transport in canals. It mainly depends on the length of the canals, the soil type or permeability of the canal banks, and the condition of the canals.
- The field application efficiency, which represents the efficiency of water application in the field
Unintended Consequences of Efficiency
It is often argued that SPIS in combination with drip irrigation will ensure that water is efficiently used at field level. Drip and sprinkler systems allow farmers to improve the timing and distribution uniformity of irrigation, which can enhance crop yields, such that transpiration per hectare increases. The prospect of higher returns per hectare, however, will encourage some farmers to expand planted area or to switch to higher-value, more water-intensive crops (Berbel and Mateos, 2014). Assuming drip irrigation will automatically lead to water savings at the farm level is a fallacy.
Water efficiency at field or farm level can also have implications at basin level. Water resource systems are highly integrated, and apparent gains (in terms of water use efficiency) in one part of the system can be offset by real losses in other parts of the system. Rainfall, surface water, groundwater, soil moisture and rates, and processes of evaporation from different land uses are all part of the same hydrological cycle and cannot be regarded as separate. Changes in water use in one domain may lead to unintended or undesirable consequences locally or downstream.
The main objective of irrigated agriculture is to increase agricultural production and consequently improve the economic and social well-being of the people using it. However, changing land use patterns due to irrigation may have other socio-economic impacts too such as land tenure, water tenure, and changes in labour inputs for construction, operation, and maintenance.
Small plots, communal land use rights, and conflicting traditional and legal land rights all create difficulties when land is converted to irrigate agriculture. Traditional land tenure arrangements are likely to be disrupted by major development and rehabilitation works (e.g. building of dams, reservoirs, and canals). The most significant impact would be the resettlement of people. This can be particularly disruptive to communities and requires sensitive project development and adequate compensation. Land use change such as new irrigation development can also negatively affect those using the land for other purposes as well as the local biodiversity. Other uses of land such as hunting, grazing, collecting fuel wood, charcoal making, or growing vegetables are negatively impacted if the same land is then used for irrigated mono-cropping agriculture. Women, migrant groups and poorer social classes have often lost access to resources and gained increased workloads. Conversely, the increased income and improved nutrition from irrigated agriculture may benefit women and children in particular.
Similar problems can arise as a result of changes to water access and infrastructure. Such developments often increase inequity in opportunity. For example, land owners benefit in a greater proportion than tenants or those with communal rights to land.
These socio-economic impacts need to be assessed and taken into account in the planning processes of irrigation schemes or their modernization. This may be less relevant for individual pumping units or projects using community-led design, planning and management. It should ensure that the needs of local communities and users are met and potential challenges are foreseen with mitigation measures in place should they arise.
Potential Health Impacts of Irrigation
The risks of water-borne or water-related disease increase in areas that lack adequate drainage of canals and soil, have unlined canals and unchecked vegetation growth, or are left with stagnant water (e.g. pits, but also on rice or sugar cane fields). For diseases, such as malaria, bilharzia (schistosomiasis) and river blindness (onchocerciasis), vectors proliferate in the irrigation waters.
Other irrigation-related health risks include those associated with increased use of agrochemicals, deterioration of water quality, and increased population pressure in the area. The reuse of wastewater for irrigation has the potential, depending on the extent of treatment, to transmit communicable diseases. The population groups at risk include agricultural workers, consumers of crops and meat from the wastewater-irrigated fields, and people living nearby.
Environmental Assessment Tools
Wise management of the environment requires an ability to forecast, monitor, measure and analyse environmental trends and assess the capabilities of land and water at different levels, ranging from a small irrigated plot to a catchment. Adoption of environmental impact assessments (EIAs) will enable countries to plan water and land use in an integrated manner, avoiding irreversible environmental damage.
The PROMOTE & INITIATE – Impact Assessment Tool, based on the ICID Environmental Check-List to Identify Environmental Effects of Irrigation, Drainage and Flood Control Projects" (Mock and Bolton, 1993) can serve as a starting point.
It is important to systematically study the current status and trends in water supply, demand, accessibility and use (FAO 2012). This is called water accounting. By evaluating return flows, measuring both basin and field efficiencies, and distinguishing between consumptive and non-consumptive savings, water accounting helps to address questions, such as: What are the underlying causes of imbalances in water supply (quantity and quality) and demand of different water users and uses? Is the current level of consumptive water use sustainable? What opportunities exist for making water use more equitable or sustainable (FAO 2016)? This assessment should be made prior to the SPIS, to establish a baseline, as well as periodically after implementation to measure the changes due to irrigation.
When assessing the impacts of solar-powered irrigation on water use efficiency, it is important to distinguish between these different levels of analysis (field/ farm/ scheme/ basin) and to carry out systematic water accounting to understand what options there are for optimising water use overall.
These efforts need to be complemented by appropriate regulation and policies. Subsidies may follow specific criteria (e.g. only in areas where groundwater is not overexploited) or provide incentives to use water, tenders may set standards (e.g. a groundwater metering system will be integrated in the solar pump), regulation may restrict SPIS use at certain times or places. If all this is considered, SPIS has the potential to fundamentally improve the lives of many people. For more information on this please refer to the 2017 FAO report The Benefits and Risks of Solar Powered Irrigation – A Global Overview.
Environmental Management Tools
Many of these negative environmental impacts can be addressed through effective planning and implementing of environmental protection and conservation measures.
Not only can negative impacts be reversed, but with an integrated management approach, further benefits can be reaped. Irrigation, for instance, can play a positive role in land use management. By intensifying food and forage production in the most favourable lands, for example, pressure on marginal lands can be reduced, using them for rain-fed agricultural production or grazing. Dams and reservoirs offer ways to mitigate the potential negative impacts of changes to flood flows but require care in planning to not disrupt the flow to downstream users and environments. Planning irrigation systems with designated flood plains and provisions for natural infrastructure, like wetlands, can improve groundwater recharge and attenuate peak discharge flows.
Further information on sustainable land, soil and water management practices can be found here: http://www.fao.org/land-water/land/sustainable-land-management/slm-practices/en/
Soil Salinity Assessment
Land Degradation Assessment
Socio Economic Checklist
PROMOTE & INITIATE – Impact Assessment Tool
- Understanding of the links between irrigation, the environment, and society
- Understanding of the risks SPIS poses to environmental flows and the options for risk mitigation
- Awareness of efficiencies in solar powered irrigation systems
- Awareness of the impacts on and roles of water rights, land rights,and gender equality in the socio-economic ecosystem
- Awareness of health impacts and delayed costs posed by poorly planned irrigation schemes and lack of adequate drainage
- Understanding of water accounting and the potential policies, subsidies, and governance systems that can produce responsible irrigation systems
- Awareness of tools available for environmental management
- Data necessary for environmental management tools
- Baseline data to monitor the socio-economic and environmental impacts of irrigation (gender data, income data, biodiversity data, employment data, water use, water quality, health data, behavioural data from government interventions, land use change, soil data, etc.)
- Irrigation planners/ system managers
- Policy makers
- Water Resources Management and Licensing Authority
- Irrigation managers, water user groups or farmer organization
- Environmental protection agencies or similar, environmental NGOs
- The far-reaching impacts, both positive and negative, of solar powered irrigation schemes
- The importance of upfront planning for drainage, public health, and inclusive basin wide development
- The need to engage in baseline data collection
- Understand the different efficiencies in SPIS and recognize the potential negative consequences
- Use nature-based solutions as measure to understand the impact of irrigation on land use, biodiversity, and potential climate change mitigation, adaptation, and resilience
- Understand that land rights, water rights, and gender issues interact with land use and agricultural productivity