Photograph by Carsten Peter, Nat Geo Image Collection
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Don't try this at home. A storm chaser plants a weather probe in the path of a tornado over fields in South Dakota.
Photograph by Carsten Peter, Nat Geo Image Collection
The Plate

How to Track a Brutal Cereal Killer: Extreme Weather

It’s no surprise that wildly swinging temperatures, droughts, and floods aren’t exactly good for crops. California’s drought cost the state’s thirsty agricultural sector $1.84 billion in 2015 alone, and the Intergovernmental Panel on Climate Change warns that a warming climate reduces yields of cereals like wheat, rice, and maize.

And with climate change messing with the frequency and intensity of at least some extreme weather events, we may be seeing more trouble for food security to come. But just how bad are these crazy weather patterns for our staple crops?

To get an answer, a team of researchers led by Navin Ramankutty, a professor of global food security and sustainability at the University of British Columbia in Vancouver, took nearly 50 years of data about weather events that disastrously affected the people near where cereal crops are grown and compared it to over 50 years of cereal crop data collected for 177 countries.

By chunking the data sets into the seven years surrounding an extreme weather event, Ramankutty and colleagues Corey Lesk and Pedram Rowhani could figure out how crops fared in the three years leading up to a disaster, the year it hit, and the three years that followed.

They discovered that droughts and extreme heat reduce cereal production by 9 to 10 percent in the countries they strike. By contrast, they couldn’t find much of an effect from floods or extreme cold.

David Lobell, a professor at Stanford University who studies food security and the environment, says that previous studies have assessed how changes in average temperature affect crops, but this study helps tease out “the relative importance of different types of extremes.”

“The nice thing about this study—and the difference between this study and others—is that it draws explicitly the connection between the disaster and the outcome,” says Chris Field, professor of environmental studies also at Stanford and director of the Carnegie Institution’s Department of Global Ecology.

Interestingly, Ramankutty’s team also discovered that droughts have been causing more damage to cereal production recently than in the past, as well as 8 to 10 percent more damage in developed countries than in developing ones.

“This was a little bit of a surprise for us,” Ramankutty says, adding that he can think of a couple of scenarios that might explain his counterintuitive results.

The first is that developed countries’ large-scale monoculture agriculture does great when the conditions are optimal but is particularly sensitive when bad weather hits. In developing countries (and in developed countries in the past), farmers may use better strategies to minimize their risk of crop failure in the face of a weather disaster—because there are fewer resources to fall back on when crops fail.

Plus, if fields in a developed country are already performing at a high level because farmers have optimized fertilizer, reduced pests, and maximized crop productivity, it’s even clearer when those crops suffer an injury.

Lobell analogizes: “If I, for example, had a leg injury, it would matter much less for my basketball performance than for [Golden State Warrior] Steph Curry’s performance, right? Because when he’s healthy, he’s really good.”

Looking toward the future, Ramankutty says that although they didn’t study this, he’s starting to think about what could happen to global food security if weather disasters start hitting more frequently and synchronously around the world. “We are able to move food around to compensate for short-term losses, but if multiple events start to strike important food baskets at the same time, it will be much harder to cope,” he says.

Field says that this more detailed analysis of climate threats to agriculture will help our food systems prepare for that potentially dire future: “Especially in this domain of adaptation, of adjusting cropping management and cropping genotypes in order to get the highest yields, it really does make a lot of difference to know what it is we’re trying to cope with.”

The entire study is published in this month’s issue of the journal Nature.

Rachel A. Becker is a science writer based in Sacramento, California. Follow her on Twitter.