Rainfall, not warming, key to crops

PUBLISHED : Friday, 06 April, 2012, 12:00am
UPDATED : Friday, 06 April, 2012, 12:00am


Rainfall has had a bigger impact than rising temperatures on the mainland's grain harvests in the past three decades, according to research by two Chinese scientists.

The researchers examined data of harvests between 1980 and 2008 and found that rice and wheat yields were both higher and lower during years of higher temperatures, suggesting the direct impact was not significant.

But the effect from higher rainfall was much more dramatic.

When there was more rain, rice yields dropped in more than one-third of cultivated areas, while wheat harvests declined in one-fifth of the cultivated land.

Maize production rose in nearly 45 per cent of land under the crop in years with higher rainfall.

Rice, wheat and maize are the country's three most important crops.

The research challenges the conventional view that rising temperatures lower cereal crops yields on the mainland, by showing that warming had no significant harmful effect on harvests, especially for rice and wheat, during the period examined by the scientists.

However, warming might still play an indirect role by exacerbating drought conditions, the scientists said.

The conclusions were first published in the Journal of the Science of Food and Agriculture last year but highlighted yesterday by research newswire EurekaAlert.

The paper is co-authored by Dr Zhang Tianyi from the Institute of Atmospheric Physics, and Dr Huang Yao from the Institute of Botany, both at the Chinese Academy of Sciences.

The annual mean air temperature increased by 1.1 degrees Celsius between 1951 and 2001, according to the paper. During the period, rainfall increased by up to 15 per cent per decade in western China, where water is abundant, but decreased in the already-dry north.

Projections from climate models suggested the mainland's mean temperature could rise by up to 3.3 degrees Celsius by 2050, while rainfall could increase by 5 to 7 per cent, the paper said.

Zhang projected that national grain output, which has risen over the last eight years, would remain relatively stable in coming years as the government invested more in agriculture but climate conditions worsened.

'Besides climatic variables, 'interventional investment', such as the use of fertilisers, will have a big impact on output,' Zhang said.

'So change in [agricultural] policy is an important factor when estimating the potential output.'

China harvested a record high of 571 million tonnes of grain last year but there have been doubts about the country's ability to keep production up in the face of more natural disasters.

Southwestern areas had their worst drought in a century two years ago, and a prolonged drought hit the middle and lower reaches of the Yangtze River, one of the mainland's major grain-producing areas, last year.