Droughts and floods: study measures how cereal harvests have shrunk

The first detailed analysis of global cereal production has shown that harvests of wheat, maize and rice have suffered greater losses since the 1980s from drought and heat compared to previous decades.

The findings question whether increased levels of carbon dioxide in the atmosphere are having a discernible “fertilising effect” on crop production that could outweigh the damaging effect on harvests caused by extreme weather events such as droughts and heatwaves exacerbated by global warming.

An analysis of national production of 16 different cereal crops in 177 countries, and a comparison with the effects of about 2,800 weather disasters between 1964 and 2007, provides a detailed snapshot of how extreme weather has affected overall cereal production globally, scientists said.

The study, reported in The Independent, found that drought and heatwaves reduced cereal harvests by between 9 per cent and 10 per cent on average in the affected countries.

The technically advanced arable farms of North America, Europe and Australia were even more strongly affected than the developing world, with average production cuts of about 20 per cent.

“We found that extreme weather disasters such as droughts and heatwaves substantially reduce crop production, and the impacts are worse in richer countries,” said Pedram Rowhani of Sussex University and a co-author of the study.

“The frequency and severity of these extreme weather events is expected to increase in the future. If we do not adapt our agricultural systems to become more resilient to these shocks we can anticipate even larger losses in the future,” Dr Rowhani said.

The analysis was published in the journal Nature.

It found that losses in average cereal producton caused by more recent droughts had increased in more recent years, with average reductions of about 13.7 per cent compared to losses of about 6.7 per cent prior to the mid-1980s. It also showed that cereal production soon bounced back after a drought year.

“We have always known that extreme weather causes crop production losses. But until now we did not know exactly how much global production was lost to such extreme weather events, and how they varied by different regions of the world,” said Navin Ramankutty, professor of global food security and sustainability at the University of British Columbia in Canada, and senior author.

The suprising finding that advanced countries  apparently are more susceptible to crop losses due to droughts and heatwaves compared to less advanced nations may reflect differences in scale and the farming methods employed in growing and harvesting cereals, the scientists said.

 

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