A globally cited statistic about the role of irrigation for food security that has formed foundational evidence for policy making and scientific research is used on a 'hearsay' basis and is based on weak evidence, according to a new study.
In a new paper published in PNAS Nexus, a team of researchers from the University of Birmingham has analysed the use of widely cited statistics, that irrigation agriculture produces 40% of global crops and withdraws 70% of global freshwater resources. These statistics have appeared in more than 3,500 documents including research and policy documents for more than 50 years, but the origins, dissemination and robustness of the 40% and 70% figures have remained unknown.
The team have found that that only 1.5% of the documents citing these statistics contain original data, and that most documents cited for evidence of the 40:70 figures either lacked evidence or did not even mention the numbers at all.
Dr Arnald Puy, Associate Professor at the University of Birmingham and lead author of the study said: "Our study indicates that the 40 and 70% numbers have spread through hearsay, probably due to their capacity to elicit a strong emotional response and to permit a seemingly simple understanding of complex, ambiguous challenges. However, real-world challenges at the food-water interface often resist characterisation with single digits and attempting to do so risks leading us astray.
"As we approach COP30 in Brazil, the time is ripe for us to critically analyse the quality of water use data at the heart of the policy debate on food security."
Significant variability
The study also shows that, according to current data, irrigation's role in global food and water security is highly ambiguous: it could be as low as 18% or as high as 50%, while its share of global freshwater withdrawals ranges from 45% to 90%. And these are just conservative estimates of the uncertainty.
Seth N. Linga, a PhD researcher from the University of Birmingham and co-author of the study commented: "The wide variability in data on the link between irrigation and food security means that irrigation can be seen either as having only a minor role in feeding the world or as being absolutely central, and likewise as highly inefficient in its water use or remarkably effective. All possibilities are supported by available data."
Carmen Aguiló-Rivera, a PhD student at the University of Birmingham and co-author, added: "Our research suggests that effort should be put into designing policies for food and water that remain solid regardless of an accurate determination of global water and food quanta. A way forward is to work with local stakeholders and communities in order to find common ground to boost crop production and save water, independently of benchmark-based calculations."
The University of Birmingham is leading research to help mitigate and adapt to the risks and impacts associated with climate change. The University has been awarded UNFCCC Observer Status which means that its experts can contribute to the vital discussions taking place at COP30.
Research at Birmingham addresses the reality of climate change through transforming health, environment, and society – sustainably supporting people and planet. Its researchers work with industry, academic and policy partners to accelerate progress on UN Sustainable Development Goals (SDGs) towards the 2030 Agenda.
