Researchers pour cold water on ideas about irrigation efficiency

Increasing the efficiency of irrigation – it seems – may not save water as common sense suggests it should.

In a Policy Forum published today in Science [open access], Australian and international experts argue that increasing efficiency simply results in more water being used on farms and less being returned to the environment.

The Science Media Centre has asked experts to comment on the article.

The results are reported HERE.

Dr Leanne Morgan, Senior Lecturer (Groundwater), Waterways Centre for Freshwater Management, University of Canterbury, comments:

“This article argues that higher irrigation efficiency does not necessarily equate to water being ‘saved’, as is often assumed. Rather, the article argues, improved irrigation efficiency at the farm scale can lead to increased water use at the basin scale.

“Additionally, the authors argue that improved irrigation efficiency can have a range of unintended consequences. One of these is reduced groundwater levels from reductions in return flows (i.e., reductions in irrigation water moving through the soil zone to groundwater). In New Zealand, there is some evidence of reductions in groundwater levels in parts of the Canterbury Plains arising from a change from low efficiency border dyke irrigation to high efficiency sprinkler irrigation.

“The reduced groundwater levels can impact spring flows and require farmers to lower wells (at considerable cost) to access the now deeper groundwater. Managed aquifer recharge is being considered as a means of augmenting groundwater levels, again at considerable cost. This is an example, additional to those provided by the authors, of the unintended consequences that might arise from irrigation efficiency initiatives designed to reduce water use.

“The authors have outlined five steps designed to assist policy makers assess whether irrigation efficiency measures are in the public interest. These five steps focus on water accounting, caps on water extractions, risk assessment, cost benefit analyses and behavioural economics. It is interesting to note here that the five steps do not explicitly consider the relationship between irrigation and groundwater quality in any detail.”

Dr Brent Clothier, Principal Scientist, Plant & Food Research; Editor-in-Chief, Agricultural Water Management, comments:

“Paradoxically, the increasing drive to increase irrigation efficiency has not saved water. This paradox is discussed in recent paper in Science which is led by researchers from the Crawford School of Public Policy of the Australian National University. The team of authors, from a range of global institutions, are all world leaders in water-resource management and policy.

“Irrigation efficiency (IE) is simply a ratio of the beneficial use of water on the farm, to the total amount of water applied by the farmer. It’s a dimensionless ratio. Nature doesn’t deal in dimensionless quantities. Nature ‘feels and lives’ by quantities – the litres of water. That’s just the denominator of efficiency – the litres of water applied. Not the ratio.

“The IE paradox is that any water saved by the individual farmers does not – global empirical evidence shows – serve to reduce water takes across the entire catchment. More people end up using the water. So, individually, the farmers might well use water efficiently but in sum the total extraction of water by the whole community of farmers across the catchment is not reduced.

“That’s the IE paradox. What’s the solution?

“There must be robust water accounting and water-take measurements. Our Resource Management Act demands there be telemetered measurements of water takes. That’s great!

“The next step in the solution is the hard one. The authors of this Science paper state that there must be a ‘cap on extractions, an assessment of uncertainties, a valuation of trade-offs, and a better understanding of incentives and behaviours of irrigators’.

“To protect our global water resources, the world’s policy people and regulators need to grasp that nettle with a strong hand.”

No conflict of interest.

Professor Troy Baisden, Bay of Plenty Regional Council Chair in Lake and Freshwater Science, University of Waikato; Principal Investigator – Te Pūnaha Matatini Center of Research Excellence, comments:

“The Policy Forum article published in today’s issue of Science highlights that commonly accepted goals of irrigation development, when translated into government policies, can lead to a counterproductive paradox. Worryingly, this paradox is embedded in the United Nation’s Sustainable Development Goals (SDGs) that drive international comparisons, as well as economic aid programmes.

“The target for water use and scarcity (SDG 6.4) focuses on monitoring and improving water-use efficiency associated with irrigation. Improved ‘irrigation efficiency’ sounds like common sense, at least when thinking about a farm. But at the scale of river catchments and aquifers, evidence has accumulated that claimed benefits of improving irrigation efficiency rarely help to ensure water is left over for amenity, ecosystem health, or downstream users.

“The reason for this is that ‘irrigation efficiency’ concept counts water that returns to streams or groundwater as waste, rather than recognising that this water has downstream benefits, which we often call ecosystem services. These benefits include supporting downstream fisheries and wetlands as well as the overall health and amenity of some the ecosystems our society recognises as most valuable – lakes, rivers and estuaries. It’s no good if greater ‘efficiency’ means less water ‘left over’ for these ecosystems, and even worse if smaller flows of water carry even greater concentrations of contaminants.

“When we read international accounts of water scarcity and irrigation, we might think they don’t apply to New Zealand. But this one does, for a number of reasons. Firstly, our drier, irrigated regions have rapidly increased the value of their agriculture and horticulture in recent decades, from dairy to wine and fruit exports. It is widely known that our freshwater available for irrigation is already fully allocated or over-allocated in these regions. Secondly, we need to consider that climate change means better growing conditions in early spring, but more demand for irrigation in summer and autumn.

“Last, irrigation development remains a political issue, with Labour and the Greens largely opposed to support for irrigation schemes in the last election, but the Government providing careful support for some through the Regional Development Fund. Water rights and ‘ownership’, as well as kaitiaki or stewardship over downstream ecosystems is another hot topic for current political debate. The impacts of water removals for irrigation, and water returned from irrigated land on downstream users and ecosystems needs to be valued, so the true costs of water use for irrigation can be considered.

“The decisions New Zealand is making now, as we start to carefully consider water scarcity, have tended to be locked in for generations in other nations. The article provides a timely five-step framework to be applied to assess whether irrigation schemes and new water allocation policies deserve government support.

“When I apply these steps to water issues we face in New Zealand, the value of water comes into focus in two areas, to offer government, councils, industry and NGOs improved clarity on irrigation policy. The first is the quantity and timing of return flows from irrigated land, as part of water that is reserved for the health of ecosystems and fisheries. Ensuring the return flows have quality criteria, and aren’t concentrated sources of contaminants matters too. Second, it could be a fallacy to keep believing that more irrigation means more production and more value. International supply chains may place greater value on the food we produce if we irrigate to maximise the reliability of our production in the face of droughts and climate change. Supply chains, as well as tourism, seem likely to also place considerable value on minimising environmental impacts.

Conflict of interest statement: Chair funded by Bay of Plenty Regional Council.

Dr MS Srinivasan, NIWA Principal Scientist – Catchment Hydrology, comments:

“One definition of irrigation efficiency used in the paper is maximising the beneficial use (i.e. water used only by the crops irrigated). This is already mandated in New Zealand as a part of the resource consent granted to the irrigator. In places like Canterbury, where the majority of the country’s irrigation happens, the regional council Environment Canterbury has started mandating that 80-100% of all applied irrigation should stay within the root zone for crop water use.

“Over the past few years, New Zealand has moved to from flood (‘border-dyke’) irrigation to more efficient spray irrigation systems that use less water to grow the same, or more, crops. However, it is also true this water saving has allowed expansion of irrigated area across the country, as has been highlighted in this paper. IrrigationNZ statistics indicates that the size of New Zealand’s irrigated area has been doubling every 12 years since 1970.

“New Zealand has already been ahead in the game by mandating metering of water takes at farm scale (for takes over 10 litres per second since 2010 and >5 litres per second since 2016). For instance, regional councils mandate measurement of extractions at the source (rivers) as well as at the delivery points (farm gates). This has been a work in progress and its real value is yet to be realised. Water metering has resulted in a large volume of data.

“While we are on the right track, we have got to go a long way in ensuring data quality and usefulness. It is necessary the knowledge gained from this data collection is communicated back to water users to ensure best use of water. Closing this loop is important for behaviour change.

“In New Zealand, irrigation efficiency is not seen on its own – just saving water or not extracting water that is not needed. It is tightly linked to water quality. For example, the good management practice guidelines by Environment Canterbury identify a good water management practice as a critical step to good nutrient management. Thus farmers are mandated to manage irrigation to not only increase efficiency but also reduce nutrient loss from farm to surface and ground waters.

“Increasingly, irrigation schemes that seek consent to extract water out of our rivers are asked to comply with and report on nutrient management practices within the scheme area.

“NIWA’s Justified Irrigation programme is addressing the core of this irrigation efficiency issue at two levels – 1. Enabling farmers to use weather forecasts to schedule their irrigation and nutrient management practices and reduce the irrigation footprint; and 2. Providing farmers an economic incentive by reducing their irrigation costs while maintaining the productivity. The environmental and economic drivers provide farmers and others a business case to use less water in achieving the same, or better, outcome.”

No conflict of interest declared.

These author comments were gathered by the Australian Science Media Centre.

Professor Quentin Grafton is a researcher at the Crawford School of Public Policy at the Australian National University. He is a UNESCO Chairholder in Water Economics and Transboundary Water Governance, is the immediate past President of the Australasian Agricultural and Resource Economics Society, Executive Editor of the Global Water Forum and Convener of the Geneva Actions on Human Water Security

“Contrary to common wisdom, increasing irrigation efficiency frequently reduces the water available for reallocation yet governments around the globe are pouring billions of dollars into making irrigation more efficient, with disastrous consequences for fresh water availability. Together with nine other scientists and economists from eight countries and seven universities, we demonstrate that increases in irrigation efficiency, in general, reduce surface run-off and groundwater recharge to the detriment of people, the environment, and our future.

“When irrigation efficiency increases, such that a greater share of the water extracted for irrigation is used to grow crops, this frequently reduces the volume of water that previously flowed back to streams and to replenish groundwater. Because this water is not consumed by irrigated crops, and therefore does not increase crop yields, it is treated as a ‘loss’ by irrigators.

“The tragedy is that these so-called unconsumed water losses to farmers are actually return flows – water that is frequently recovered and reused elsewhere in a watershed or basin. They have value. The key point, and the paradox, is this: advanced irrigation technologies that increase irrigation efficiency frequently increase on-farm water consumption and groundwater extractions and reduce return flows.”

Quentin has not declared any conflicts of interest.

John Williams is an Honorary Professor in the Crawford School of Public Policy at The Australian National University. He is the  former Commissioner of the NSW Natural Resources Commission, former Chief Scientist in the NSW Department of Natural Resources and former Chief of CSIRO Land and Water.

“Our Science paper provides five key steps to respond to the unfolding global water challenge and look at how to reverse the tide of bad policy. First and foremost, physical water accounts are needed from the farm scale to the basin scale to make transparent ‘who gets what and where’. Second, reductions in irrigated water consumption require decreases in water extractions and limits on the irrigated area.

“The other three steps to avoid a global water tragedy include: valuing water (including in-stream flows) to ensure that the public benefits of irrigation efficiency subsidies exceed the costs; risk assessments of the effects of increases in irrigation efficiency, including uncertainties over inflows and outflows; and a much better understanding of how irrigators’ actions change as their irrigation efficiency increases.”

John has not declared any conflicts of interest.

Source: Science Media Centre

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