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The new study reports that the amount of irrigated land could in fact increase to as high as 1.8 billion hectares (4.4 billion acres)

Expansion of irrigation to cater for future population ‘greatly underestimated’

Image credit: Wynand Uys on Unsplash

New research suggests that the amount of farmland that will need to be irrigated in order to feed the global population by 2050 could be up to several billion acres, far higher than scientists currently project.

According to the international study, this growth would result in a far greater strain on aquifers, a body of permeable rock which can contain or transmit groundwater, as well as the likely expansion of agriculture into natural ecosystems as farmers search for water.

Existing irrigation models – which are widely used to define policies on water and food security, environmental sustainability, and climate change – suggest that the amount of agricultural land requiring irrigation could extend between 240 million and 450 million hectares (590 million to 1.1 billion acres) during the next 30 years.

However, those projections likely underestimate growth in population – estimated to reach around 9 billion by 2050 – and too confidently assume how much land and water will be available for agriculture without having to find new sources, according to researchers from Princeton University, the University of Reading, and the University of Bergen in Norway.

The quantity of irrigated land could, in fact, increase to as high as 1.8 billion hectares (4.4 billion acres), the researchers said. “Policymakers should acknowledge that irrigated areas can grow much more than previously thought in order to avoid underestimating potential environmental costs,” they wrote in the journal Geophysical Research Letters.

Arnald Puy, a postdoctoral researcher in ecology and evolutionary biology at Princeton, said that an expansion of irrigation of this magnitude would have dramatic effects on the environment and other sectors of society. He worked alongside Samuele Lo Piano of the University of Reading and Andrea Saltelli of the University of Bergen on the research.

According to experts, irrigation is currently responsible for about 70 per cent of freshwater withdrawals worldwide. Around 90 per cent of water taken for residential and industrial uses eventually returns to the aquifer, but only about one-half of the water used for irrigation is reusable. Meanwhile, evaporation, evapotranspiration from plants, and delivery losses such as from leaky pipes forever remove the rest from the water cycle.

“Much larger irrigated areas might mean extending agricultural land toward new ecosystems or non-cultivated areas with the consequent loss of biodiversity, which might also be larger than expected,” Puy said. “At the same time, needing more water for irrigation means less water for other sectors and therefore more stress on water resources than expected.”

Puy added that there could also be a much higher amplification of climate change, which current climate models do not account for.

Previous research has shown that irrigation may influence climate by altering surface temperatures and the amount of water vapour in the atmosphere, both of which are critical components of climate modelling. These factors have an impact on cloud formation and the amount of solar radiation that is either contained within the atmosphere or reflected back into space, experts have said.

The climate effects of irrigation also include greenhouse gases released through producing and operating irrigation machinery. Moreover, the most common modern equipment consists of centre-pivot systems consisting of wheeled tubes outfitted with spray guns or dripping faucet heads that rotate around a central water source.

“Much larger irrigated areas means that predictions of agricultural gas emissions might also be much lower than they will be in reality,” Puy explained. “More irrigated areas means investing on irrigation machinery and energy consumption, leading to the consumption of fossil-energy reservoirs and the release of CO2.”

Irrigated agriculture also increases soil total nitrogen and carbon due to the addition of fertilisers and manure. Nitrate leaching can taint groundwater and ammonia can be volatilised from fertilisers, limiting the availability of potable water, Puy said.

By drawing attention to the underestimation of irrigated land by current models, Puy, Lo Piano and Saltelli hoped to increase the accuracy of all studies that rely on those estimates to project how the climate and environment could be affected by the challenge of feeding everyone on Earth – while investigating how the state of the environment could shape the outcome of that effort.

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