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Study: Heat, drought led to losses of 3 billion tons of world's cereal crops from 1964 to 2007

A new study has found that nearly a tenth of cereal crops have been wiped out due to droughts and heat waves between 1964 and 2007.

While it is no surprise that extreme weather events have an impact on crop production, this study aimed to determine how much and what that will mean in the future.

Navin Ramankutty, a professor at the University of British Columbia and an author of the study, stated that they used two sets of data: a crop area, yield and production data from the Food and Agriculture Organization and approximately 2,800 weather disaster reports from the Emergency Events Database.

The authors looked separately at cereal crops, including maize, wheat and rice, in the study.

"We found that all three [crops] were equally affected by droughts, but only maize had a strong significant impact from extreme heat," Ramankutty said. "This result was a bit perplexing and we had several caveats about it [in the paper]."

They estimated that a loss of more than three billion tons of cereal crop production from 1964 to 2007 due to droughts and heat waves.

"Our estimate is that every drought or extreme heat event reduces current cereal production by roughly 9-10 percent. In the future, it is anticipated that, with climate change, we will have more extreme heat events and potentially more droughts as well [although the latter is a bit more controversial]. So, we can extrapolate that there will even greater cereal production losses in the future," Ramankutty said.

The authors found that crops in developed countries were more affected than in underdeveloped countries.

"Agricultural systems of North America, Europe and Australia suffered most from droughts, facing on average 19.9 percent production deficit compared to 12.1 percent in Asia, 9.2 percent in Africa and no significant effect in Latin America and the Caribbean," as stated in the paper.

The authors gave three possible explanations for this pattern.

"First, it may arise from a tendency among lower-income countries to encompass diverse crops and management across many small fields, which may allow for some fields to resist drought better than others," the study said. "Second, lower-income countries may better resist drought because smallholders tend to use risk-minimizing strategies compared to the yield-maximizing ones prevalent in higher-income countries. Third, the pattern may relate to generally lower fair-weather yields in lower-income countries."

Along with developed countries being affected more than underdeveloped countries, the authors found that more recent droughts (1985-2007) had stronger impact and were more severe on cereal production than earlier ones (1964-1984). However, they were not able to tell whether the increase could have been due to droughts getting more severe or limitations in earlier data sets.