Efficiency Projects

DOES IMPROVED IRRIGATION TECHNOLOGY SAVE WATER?

A REVIEW OF THE EVIDENCE

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS CAIRO, 2017

REPORT – Does Improved Irrigation Technology Save Water?

“The traditional assumption has been that increasing irrigation efficiency through the adoption of modern technologies, like drip irrigation, leads to substantial water savings, releasing the saved water to the environment or to other uses. The evidence from research and field measurements shows that this is not the case. The benefit at the local “on-farm” scale may appear dramatic, but when properly accounted at basin scale, total water consumption by irrigation tends to increase instead of decreasing. The potential to increase water productivity—more “crop per drop”—is also quite modest for the most important crops.

These findings suggest that reductions in water consumption by irrigated agriculture will not come from the technology itself. Rather, measures like limiting water allocation will be needed to ensure a sustainable level of water use.

Improved irrigation technologies include mostly piped delivery systems, laser levelling of fields, conversion to pressurised systems for sprinkler, drip, or sub-surface drip. In each case, the objective is to replace traditional, “inefficient” irrigation with techniques that maximise beneficial water use by the crop, and improve the timing and reliability of water deliveries.

These innovations are expected to generate two major benefits:

• water is “saved” and released to other uses
• more production is achieved per unit of water

Headlines claiming (say) 50 percent water savings through better technology invariably refer to a narrow “local” perspective of water applied to the field, failing to account for return flows that recharge aquifers or contribute to downstream river flows. If the underlying aquifer is saline, or outflow goes straight to the sea, then savings are real, but only a complete set of water accounts will reveal whether real water savings are achieved, so that water can be released to other users with no negative effects.

For a given crop and given agro-climatic conditions, the relationship between water consumed and crop production is linear. The important implication of this relationship is that if yield per unit area increases, then it is likely that water consumption also increases.

On the other hand, if hi-tech irrigation allows the farmer to grow higher value crops, we are interested in another indicator: economic water productivity. Here the evidence is stronger that hi-tech (which often ensures more controlled and better timed irrigation supplies) is one of the various factors that encourages farmers to invest in higher return crops.

Hi-tech irrigation (broadly defined as any technical intervention designed to improve water delivery on farm) has many benefits to the irrigator: water application is reduced, pumping costs are reduced; fertilisers and other chemicals are saved and pollution is reduced; labour costs are often lower (employment drops); and cropping options are wider. Are these benefits, derived from improved irrigation technology, providing also ‘water saving’ at watershed or national scale? The answer to this question is relevant where water is scarce, and especially where aquifers are over drafted and rivers are drying.

In the process of writing this paper, more than 150 experts were addressed with requests for evidence of the impact of hi-tech irrigation on water consumption and water productivity. This review indicates, somewhat surprisingly, that there are rather few examples of carefully documented impacts of hi-tech irrigation, while there are many examples of projects and programmes that assume that water will be saved and productivity increased. Such studies as do exist, are either inconclusive or, more often, show that water consumption actually increased (as science would predict) when irrigation systems were upgraded, and that productivity per unit of water consumed was more or less constant.

The conclusion of this report is that restoring a balance between sustainable supply and consumption of water requires first physical control of the water resource by government or other agencies responsible for sustainable use, followed by interventions to reduce allocations. Within the allocated and controlled quotas, hi-tech irrigation will evolve and spread to the extent that it makes sense for the farmer who wishes to take advantage of the various benefits of hi-tech irrigation. However, introducing hi-tech irrigation in the absence of controls on water allocations will usually make the situation worse: consumption per unit area increases, the area irrigated increases, and farmers will tend to pump more water from ever-deeper sources. This implies that controlled access to water must precede introduction of hi-tech irrigation.

Jevons’ paradox, predicting that improved efficiency of resource use tends to increase consumption and demand for that resource, applies also to water. It cannot be claimed that exceptions to these general conclusions do not exist, and revisions to this paper incorporating such cases will be welcome. Meanwhile, this wide-ranging search for examples suggests that the conclusions stated above should be the default assumption—the null hypothesis—against which project and programme designs should be tested.”