Understanding and Improving Irrigation Efficiencies

Water is the lifeblood of agriculture, yet a significant portion of it never reaches the crop. From the moment water is stored in a reservoir to the point it is absorbed by plant roots, losses occur at every step. Irrigation efficiency is the measure of how much of that water actually serves its intended purpose – supporting crop growth. Understanding and improving this efficiency is one of the most practical strategies available to farmers and water managers for producing more food with less water.

What is irrigation efficiency? 🔗

Irrigation efficiency is defined as the ratio of water used to meet the consumptive requirements of a crop – plus the amount needed to maintain a favourable salt balance in the root zone – to the total volume of water diverted, stored, or pumped for irrigation. Any water applied that is not made available to plant roots is considered wasted, and directly reduces efficiency. The key insight is that efficiency is not a single number but a chain of three inter-linked components: reservoir storage efficiency, water conveyance efficiency, and water application efficiency. Each component has its own loss pathways, and weaknesses in any one of them drag down the overall result.

Reservoir storage efficiency 🔗

The journey of irrigation water begins at a storage structure – a farm pond, tank, or reservoir. Reservoir storage efficiency measures how effectively water is retained in storage before it is even released for irrigation. It is expressed as the ratio of water actually stored in the reservoir to the water that should have been stored during a given period. Losses at this stage occur due to evaporation from the water surface, seepage through the reservoir bed and embankments, and operational spills. These losses can be substantial, especially in shallow reservoirs in hot, dry climates where evaporation rates are high.

Improving reservoir storage efficiency involves good reservoir design and management – including adequate storage depth to reduce the surface area-to-volume ratio (which limits evaporation), lining or compacting the base to reduce seepage, and regular monitoring of sediment accumulation that reduces usable storage capacity over time.

Water conveyance efficiency 🔗

Once water leaves the reservoir, it travels through a network of canals, channels, and pipes before reaching farm fields. Water conveyance efficiency (Ec) is the ratio of water delivered to the farm or field to the water diverted from the reservoir or source. Mathematically:

Ec = (Water delivered to the field ÷ Water diverted from the reservoir) × 100

The difference between the two figures represents seepage into canal banks, evaporation from open water surfaces, operational spills, and leaks in pipelines. According to FAO, conveyance efficiency depends heavily on canal length, the permeability of canal bank soils, and the condition of the canal infrastructure. Longer canal systems in sandy soils without lining can lose a very large fraction of water before it reaches farmers. When canals are lined with concrete, brick, or plastic, losses drop dramatically.

Sources of conveyance losses 🔗

Water losses in irrigation canals arise from several causes: evaporation from the water surface, deep percolation to soil layers below the canal, seepage through embankment bunds, overtopping of bunds, bund breaks, and even damage from burrowing animals. Among these, seepage through unlined earthen channels is consistently the largest source of loss. Conveyance losses are much lower for closed conduits and buried pipelines, which is why shifting from open earthen channels to piped distribution systems is one of the most effective interventions for improving conveyance efficiency.

Water application efficiency 🔗

Water application efficiency (Ea) measures how much of the water delivered to a field is actually stored in the crop root zone and made available to plants. It is expressed as:

Ea = (Water stored in root zone ÷ Water delivered to the field) × 100

Losses at this stage include surface runoff from the field, deep percolation below the root zone, evaporation from the soil surface and from sprinkler droplets in the air, and drift losses in windy conditions. For surface irrigation systems, deep percolation and surface runoff are the dominant losses and can reduce application efficiency to below 50% if the system is not managed carefully. Sprinkler and drip systems reduce – but do not eliminate – these losses.

Application efficiency by irrigation method 🔗

The choice of irrigation method has the single largest influence on application efficiency. Traditional flood and furrow irrigation typically achieves application efficiencies in the range of 40-60%, as large volumes of water run off the field or percolate below the root zone before the soil is adequately wetted. Sprinkler systems perform better, generally in the 60-80% range depending on design and management. Drip and subsurface drip irrigation systems achieve the highest application efficiencies, typically 85-95%, by delivering water slowly and directly to the root zone, minimising evaporation, runoff, and deep percolation.

Overall or scheme irrigation efficiency 🔗

When reservoir storage efficiency, conveyance efficiency, and field application efficiency are combined, the result is the overall or scheme irrigation efficiency. It represents the fraction of water pumped or diverted at the scheme inlet that is actually used beneficially by crops. The scheme irrigation efficiency (E) is calculated as:

E = (Ec × Ea) ÷ 100

As a benchmark, a scheme irrigation efficiency of 50-60% is considered good, 40% is reasonable, and 20-30% is poor. In practice, major irrigation projects in India report overall efficiencies between 35-40%, which points to enormous scope for improvement – and partly explains the gap between the irrigation potential created and the area actually irrigated productively.

Water distribution efficiency 🔗

A related concept is water distribution efficiency (ηd), which measures the uniformity of water penetration across an irrigated field. Even if the right total volume of water is applied, uneven distribution means some areas are over-irrigated while others remain under-watered, reducing both crop performance and water productivity. Distribution efficiency is highest when water penetrates to a uniform depth across the entire field. Techniques such as land levelling, properly designed furrow lengths, and careful flow management improve distribution uniformity.

Why improving irrigation efficiency matters 🔗

Agriculture accounts for roughly 70% of global freshwater withdrawals, and in many developing nations this share is even higher. Improving irrigation efficiency means more crop production from the same water supply – not necessarily reducing total withdrawals, but extracting far more value from every litre used. Studies suggest that improvements in irrigation efficiency alone could meet half of the projected future increase in agricultural water demand, making it one of the most cost-effective responses to growing food and water stress.

Practical strategies for improving irrigation efficiency 🔗

Lining canals and upgrading conveyance infrastructure 🔗

One of the most direct ways to improve conveyance efficiency is lining open earthen channels with concrete, brick, or plastic. This reduces seepage sharply. Going further and replacing open channels with buried pipelines is even more effective, as pipelines eliminate both seepage and evaporation losses entirely. Shifting from gravity-fed open channel systems to pressurised piped delivery is now widely recommended as a foundational upgrade for irrigation modernisation.

Adopting efficient irrigation methods 🔗

Upgrading the field application system is often the highest-impact investment. Drip irrigation delivers water directly to the soil at the base of each plant, eliminating losses from wind drift, evaporation, and surface runoff that affect sprinkler and flood systems. Research confirms that under water-scarce conditions, drip irrigation maintains crop yields while using significantly less water than other methods. Subsurface drip irrigation goes further by burying the drip lines below the soil surface, reducing surface evaporation and encouraging deeper root growth.

Irrigation scheduling and timing 🔗

When irrigation is applied matters almost as much as how it is applied. Irrigating during the hottest part of the day leads to significant evaporative losses. Scheduling irrigation for early morning or evening, when temperatures are cooler, reduces these losses. Precision or climate-smart irrigation – using soil moisture sensors, weather-based advisory services, and automated systems – ensures that water is applied only when crops genuinely need it, in the right amount, at the right time.

Deficit irrigation 🔗

Deficit irrigation – supplying water at below full crop-water requirements at carefully chosen growth stages – is another approach for raising water productivity. While it requires detailed knowledge of crop-water stress responses, it has been shown to increase the yield of crop per unit of water consumed, particularly for drought-tolerant varieties. This is a deliberate strategy to improve water use efficiency rather than simply maximising applied water.

Regular maintenance and monitoring 🔗

Many irrigation systems underperform not because of poor design but because of poor maintenance. Cracked canal linings, worn pipe joints, blocked emitters, and unrepaired bund breaks all create losses that accumulate over time. Regularly measuring water inputs and comparing them against the water actually stored in the root zone reveals where the biggest losses are occurring and directs maintenance resources where they will have the most impact.

The bigger picture 🔗

Irrigation efficiency is not a fixed characteristic of a farm – it is the outcome of a series of decisions about infrastructure, technology, scheduling, and management, made at every stage from the reservoir to the root zone. Each incremental improvement in storage, conveyance, or application efficiency compounds into a meaningfully higher overall efficiency. In a world where freshwater resources face growing pressure from population growth, climate variability, and competing uses, lifting irrigation efficiency is one of the most direct paths to producing more food without withdrawing more water.

What do you think? Given that overall irrigation efficiency in many large projects remains below 40%, where do you believe the most urgent improvements should be made – in conveyance infrastructure, field application methods, or management practices? And how realistic is it for smallholder farmers to adopt high-efficiency systems like drip irrigation without stronger policy and financial support?

References

1. https://ecoursesonline.iasri.res.in/mod/page/view.php?id=124852
2. https://lgpress.clemson.edu/publication/the-basics-of-irrigation-reservoirs-for-agriculture/
3. https://www.fao.org/4/t7202e/t7202e08.htm
4. https://passel2.unl.edu/view/lesson/bda727eb8a5a/8
5. https://www.saiplatform.org/uploads/Modules/Library/sai-technical-brief-15-drip-irrigation-and-water-scarcity-2.pdf
6. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/irrigation-efficiency
7. http://ecoursesonline.iasri.res.in/mod/page/view.php?id=124852
8. https://www.journals.uchicago.edu/doi/full/10.1093/reep/reaa004
9. https://www.mdpi.com/2624-7402/7/4/106
10. https://climate-adapt.eea.europa.eu/en/metadata/adaptation-options/improvement-of-irrigation-efficiency
11. https://www.smsfoundation.org/what-is-a-drip-irrigation-system-and-how-does-it-help-to-save-water/
12. https://www.mdpi.com/2073-4441/15/9/1733