Scientists in the United States have this week warned that, as the world's drylands become even drier, water will not be the only resource in short supply. On Wednesday, researchers from the Northern Arizona University published a study in the journal Nature warning that levels of soil nutrients are also likely to be affected by climate change, and their imbalance could affect the lives of one-fifth of the world's population.

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Climate change is expected to result in wet regions becoming wetter (for the UK this could mean more rain, falling less often but in more concentrated bursts) and water scarcity increasing in other areas - including Arizona. Last year, global analysis (the results of which were also published in Nature) revealed that demand for water has outpaced supply in many of the world's key agricultural regions – a quarter of the global population lives in these regions. 

The global irrigated area has also reached record levels, putting further pressure on aquifers.

The Arizona researchers' study reveals how soil changes may occur and discusses the implications for those living in drier regions. Co-author Matthew Bowker, assistant professor of forest soils and ecosystem ecology at Northern Arizona University has been investigating the often overlooked issue since 2009. Bowker's project studied 224 locations in 16 countries across every continent except Antarctica.  

Professor Bowker explained that most of the 17 nutrients that plants need to grow to their potential are soil resources, such as nitrogen and phosphorus. The statistical model he helped develop for the study suggests that as the climate becomes more arid, nitrogen will decrease and phosphorus will increase, meaning soils will become more inhospitable for plants.

"Both are essential for plant growth, and both are typical components of fertilizer, but both need to be around in the right quantities for plant growth to proceed most efficiently," he said. "It's like a situation where you're making hamburgers but run out of beef. You can't just slip in another bun and still produce a hamburger."

Drylands cover about 41 percent of the earth's surface. The study suggests that people who depend on those ecosystems for crops, livestock forage, fuel and fiber will find their resources increasingly restrained. In some areas, reductions in plant production could have other side effects, or exacerbate changes such as soil erosion - Bowker used Arizona as an example of where the impacts of climate change could be magnified. Here, he said, reduced production could magnify the impact of dust storms, which have been increasing in recent decades.

"We can probably expect more and more dust in the air," he said.

The Arizona professor worked with colleagues at a number of other institutions to produce his research; he said, "This is a testament to the power of networked science," adding that it would have been "prohibitively expensive" for any one researcher or research group to complete the project.