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In response to excessive water development leading to economically marginal and environmentally detrimental supply-augmentation projects, water demand management (WDM) has acquired wide currency in mainstream policy circles. By virtue of the negative images often associated with large infrastructure, demand management appears as a desirable and consensual softer, cheaper and greener option that nobody is opposing. Many institutions and scientists consider that water demand principles provide "a guide for moving from scarcity to sustainability" and entertain the idea that agriculture, in particular, can (and as the biggest water user, should) produce 'more with less' water. But what has WDM really achieved in practice in the agricultural sector? What is its quantitative contribution to addressing the water crisis and reducing water consumption?

A few years ago, Brian Richter and colleagues (2017) undertook, in their own words, "a comprehensive literature and internet survey" of water-saving strategies in irrigated agriculture. They found that "there is in fact considerable potential to reduce consumptive water use in irrigation systems". (They also looked at cases of reallocation to other uses but since these transfers do not really save water, I am not discussing such cases here). They found 30 cases of water-saving measures, 10 of which being cases of "reduced water application". Examples of reduction in beneficial and/or non-beneficial consumption included cases of non-till farming, mulching, replacing open canals with pipes, irrigating at night rather than during the day, removing invasive and/or aquatic vegetation, and regulated deficit-irrigation. To which they added cases in which shifting from a given crop to a less demanding one would save water (they do not question why this is not happening in practice). Such inventories are welcomed and remind us of the various possible adjustments to scarcity, however marginal. Many are indeed implemented by the users themselves when faced with water shortages.

I feel, however, that the belief that such measures and practices can make a difference and their potential is indeed 'considerable' is very much a question of seeing the glass '20% full' or '80% empty'. Cumulative evidence from studies of closed/overexploited basins and aquifers puts me, however reluctantly, on the side of those who see the glass as 80% empty (at best).

Demand-management measures frequently come with constraints and are therefore not popular with either end-users nor managers and politicians. On the contrary, supply augmentation caters to the private interests of users, water bureaucracies, politicians, construction companies and development banks and is 'hard to beat'. Often unpalatable demand management options (such as pricing) will thus tend to be considered only after supply options are exhausted, and well after water scarcity has built up and overabstraction of surface water beyond environmental flows, and of groundwater beyond its safe yield, has become structural. This means that the basin is already largely closed, aquifer levels are dropping at alarming rates, while return flows, (even when polluted) have long been tapped and (re)used wherever possible, thanks in particular to increasingly cheap pumping devices. This hydrological reality, also recognized by Richter and colleagues, means that the gains that can be expected from measures that reduce the volume of water applied, or even non-beneficial consumption, are often minimal, in both absolute and relative terms.

Indeed, as allocation evolves towards a zero sum game (oftentimes a negative sum game, when heavy groundwater depletion is observed), the benefits derived from consuming water can be reallocated and spatially shifted; but water scarcity and overdraft can, increasingly, only be dealt with through a reduction in evapotranspiration. This is indeed what happens sooner or later: (some) farmers are pumped out or affected by droughts and exit the agricultural sector, groundwater-dependent vegetation dies, and wetlands dry up. Unless it effectively works to reduce evapotranspiration (e.g. through fallowing programmes), demand-management can do little at this stage and the supply-demand gap ends up materializing in dramatic ways.

To avoid the political costs of reducing the water-based stream of benefits to both small farmers and corporate investors, national decision-makers as well as development banks, international institutions, and environmentalists have unanimously promoted technical fixes, which are usually state-subsidized. The most popular ones include wastewater reuse, canal lining and irrigation 'modernization' (e.g., shifting from gravity to pressurized systems). Leaving aside treated wastewater reuse (and glossing over the fact that much wastewater is actually already used[1]), the promotion of drip irrigation and lining is typical of agricultural water demand-management policies mistakenly geared towards reducing the amount of water applied rather than its consumption.

Although drip irrigation does a lot of good things that may make it desirable (it reduces labour needs, increases yields, allows for fertigation, etc), it is by and large 'neutral' in terms of water consumption for any given crop (see a recent review by FAO: Perry and Steduto, 2017). Furthermore, intensification through drip tends to create a 'rebound effect', with expansion of cultivation where land is available, but also higher rates of water consumption per unit of land (diversification to more water-demanding crops, increase in cropping intensity, etc): much the opposite of what it claims to achieve. Where fruit trees expand, demand is made more rigid at the very moment climate variability dictates more flexibility, and risk increases. Likewise, canal lining eases distribution and enhances head-end/tail-end equity but reduced infiltration may further upset the groundwater balance and impact groundwater appropriators.

Arid and semi-arid countries like Australia, Spain, Morocco, Egypt and Iran, to take only a few illustrations, have spent billions of dollars to 'modernize' irrigation while officially (and loudly) claiming to 'save' billions of m3. However, they have critically failed both to control expansion of water use and to reduce evapotranspiration (consumption). These massive subsidies are now coming under scrutiny and being hotly debated in terms of what 'savings' they have actually achieved (see Australia, Spain or Morocco). Meanwhile, the EU has now realized that 'modernization' must come together with control of use in order to avoid perverse effects; and the World Bank has introduced water balance as a mandatory step of water projects (but struggles to implement it).

Irrigation demand management is, yes, needed and does have potential in some specific situations, e.g., where return flows go to saline aquifers or are lost to wasteland, or through the adaptation of crop types or farming techniques. In not-too critical situations, like in some regions of Europe, sustainability can sometimes be restored through a gamut of measures (which more often than not include also some additional storage or transfers). But we should not entertain the hope that WDM will constitute a fix to many deeply unsustainable uses of water, most particularly groundwater. Modernize – if you want – but do not pretend (with some exceptions) that it will 'save water'. Shoddy hydrology associated with wishful thinking can defer (political) costs, but they cannot 'invent new water'.

References

Berbel, J.; Gutiérrez-Martín, C.; Mateos, L. 2019. Effects of the irrigation modernization in Spain 2002–2015. Water Resources Management 33: 1835–1849.

Grafton, Q.; Colloff, M.J.; Marshall, V. and Williams, J. 2020. Confronting a 'post-truth water world' in the Murray-Darling Basin, Australia. Water Alternatives 13(1): 1-27, Abstract | Full Text - PDF

Grafton, R. Q., Williams, J., Perry, C. J., Molle, F., Ringler, C., Steduto, P., Udall, B., Wheeler, S. A., Wang, Y., Garrick, D., & Allen, R. G. 2018. The paradox of irrigation efficiency. Science, 361(6404), 748–750.

Molle, F. and Tanouti, O. 2017. Squaring the circle: impacts of irrigation intensification on water resources in Morocco. Agricultural Water Management 192(2017): 170-179.

Perry, C.J., Steduto, P. 2017. Does improved irrigation technology save water? A Review of the Evidence. Regional Initiative Series No. 4. FAO, Regional Office for Near East and North Africa, Cairo, Egypt.

Richter, B.D.; Brown, J.D.; DiBenedetto, R.; Gorsky, A.; Keenan, E.; Madray, C.; Morris, M.; Rowell, D.; Ryu, S. 2017. Opportunities for saving and reallocating agricultural water to alleviate water scarcity. Water Policy 19(5): 886–907.

Perry, C. 2021. Review of "Dead in the water. A very angry book about our greatest environmental catastrophe… the death of the Murray-Darling Basin". Allen & Unwin, 2021, by Richard Beasley, Water Alternatives, www.water-alternatives.org/index.php/boh/item/211-dead


[1] Which does not diminish the need to treat it of course.