China's farming calendar 'out of step' with global warming

Yidong Gong in SciDev.net: The traditional Chinese farming calendar, still used by millions of farmers to guide their farming activities, should be adapted to reflect global warming, say scientists. The 24 'solar terms', a set of timings reflecting the seasonal cycle, were laid down 2,000 years ago as a supplement to the traditional Chinese calendar. They are marked on the calendar under specific dates — two terms per month — and refer to agricultural activities.

The terms, which mark seasonal transitions and indicate the stages crop growth, include 'great cold', 'great heat', 'rain water', 'waking of insects' and 'grain in ear'. They are used alongside modern agro-meteorological data to plan agricultural activities. In rural areas, many proverbs and songs associated with the terms are also used.

But now, Chinese meteorologists say the traditional divisions no longer apply because they do not take climate change into account. The researchers collected air temperature data from 549 meteorological stations across the country from 1960 to 2008 to determine how the mean temperatures indicating seasonal transitions have changed.

They found that the mean temperature in China has risen substantially, with spring and summer starting earlier, and autumn and winter having a later onset. Summer has lengthened by 15 days, while winter has shortened by the same amount. Such a dramatic change means the farming practices associated with the solar terms need to be adjusted, they say. The number of cold days for 'great cold' has reduced by 56.8 per cent over the past ten years compared with the 1960s, for example, whereas the number of hot days for 'great heat' has increased by 81.4 per cent....

A harvest in China, shot by Steve Evans, Wikimedia Commons, under the Creative Commons Attribution 2.0 Generic license