Better Water Management Could Halve Food Gap

"This study is the first to systematically quantify potential contributions of different strategies of farm water management to increase global crop production without increasing pressure on land and water boundaries," 

Jonas Jägermeyr of the Potsdam Institute for Climate Impact Research, Germany toldenvironmentalresearchweb. "While we can reproduce the effect of crop water management demonstrated by case studies, we are in fact surprised to see sizable effects at the global level – without expanding agriculture into forest or using up more water resources."

Jägermeyr and colleagues from Germany, Kenya, Australia and Sweden used the LPJmL dynamic global agro-biosphere model to come up with the results, in conjunction with 20 climate models and four representative concentration pathways, and either allowing for or ignoring any beneficial effects of carbon dioxide on crop growth.

"Locally, the huge potential of crop water management to increase crop yields, food security and climate resilience of agriculture has been demonstrated repeatedly," said Jägermeyr. "But every farming system is different, there is huge heterogeneity across watersheds and across cultures. In addition, upstream–downstream effects along rivers make the assessment of large-scale management implications truly complex."

This means that up-scaling the potential of integrated crop water management to a watershed level and then to the global level is "everything else but trivial". The model employed must be "process-based, coarse enough to allow global simulations, while…sufficiently detailed to represent such complexity and mechanistic dependencies".

Together, an "ambitious" scenario of improving irrigation efficiency and the use of rainwater could boost global crop production by 41% and close the water-related yield gap by 62%, the model showed. Irrigation could be enhanced by employing drip-feeds and sprinkler systems, whilst measures such as mulching, conservation tillage and micro-catchment systems like pitting, terracing and micro-basins could boost the efficiency of rainwater use.

"Despite the fact that many case studies and regional suitability assessments highlight the great potential associated with crop water management, it is still not part of a high-level international agenda and its potential is as yet underestimated at the global level," said Jägermeyr. "The recently renewed 'Sustainable Development Goals' stipulate sustainable agriculture among all nations, but this is based on little evidence of how to achieve it, and they do not focus on crop water management at all. In a recent  Nature  Comment, Johan Rockström and Malin Falkenmark urge [a] focus on rainwater management to achieve sustainable agriculture and call for a global systematic quantification."

More than 800 million people are chronically undernourished, according to a United Nations report published in 2015. A 40% increase in calorie production by 2050 – as potentially feasible with better water management – could be enough to halve the widening global food gap, the researchers believe, assuming that we need 60–100% additional crop calories to eradicate hunger.

"It is beyond the scope of this study to investigate potential intensification of water withdrawals for irrigation above the current level," said Jägermeyr. "In water-scarce regions this would transgress the planetary boundary for freshwater and is thus not advisable. But in many other regions there is still lots of room for expansion, especially in sub-Saharan Africa [where] only 5% of the cropland is currently under irrigation, but at the same time there is huge potential to transform water-limited rainfed systems into irrigated systems by using previously untapped renewable water resources."

But Jägermeyr adds that to achieve this in a sustainable manner, we must quantify local planetary boundaries for freshwater use and define how much water must remain in rivers to sustain their ecosystems. This is what the team will address in future work.

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Taxonomy

• Water Supply
• Water Management