Droughts in China have historically been more likely to trigger peasant revolts than floods, according to research by Professor Ruixue Jia, published in the March 2014 issue of the Economic Journal. Her study finds that while both kinds of ''weather shock'' significantly raised the prices of grains (wheat and rice), the price effect of droughts was nearly three times that of floods. The introduction of sweet potatoes, a drought-resistant crop from the Americas, led to a considerable reduction in civil conflict.
To what extent did weather shocks cause civil conflict in past societies – and to what extent did the historical introduction of drought-resistant crops mitigate these effects? Professor Jia investigates these questions using data on more than two hundred prefectures in China over four centuries (a much longer span of than related studies using modern data on periods of 20 to 30 years).
She examines the effect of the introduction of sweet potatoes, a drought-resistant crop that survives bad weather better than wheat and rice and also provides more calories per unit of land. The availability of sweet potatoes translated into greater agricultural production, especially in bad weather conditions. What''s more, the link between droughts and peasant revolts became weaker in regions that adopted the new crop.
Before the introduction of sweet potatoes, exceptional droughts increased the probability of peasant revolts by around 0.7 percentage points, which translates into a probability of revolt in drought years that is more than twice the average probability of revolt. After the introduction of sweet potatoes, exceptional droughts only increased the probability of peasant revolts by around 0.2 percentage points.
In recent years, historians, climatologists and economists have found evidence of a link between weather-induced economic decline and conflict based on case studies or cross-country data. Historical China provides a good testing ground for this link as there is detailed information on abnormal weather conditions and the occurrence of peasant revolts – a proxy for civil conflict – at the prefecture level going back to the 15th century.
Professor Jia comments:
''My findings are based on historical data, but they may shed light on the modern world. Sweet potatoes stabilised historical China because they constituted a low-cost technology that benefited the poor.
''Some recent studies suggest that foreign aid may increase the chance of armed conflict in African countries. One can imagine that the effect of technical aid that benefits the poor might be very different from that of monetary aid.''
''Weather Shocks, Sweet Potatoes and Peasant Revolts in Historical China'' by Ruixue Jia is published in the March 2014 issue of the Economic Journal. Ruixue Jia is an assistant professor at the School of International Relations and Pacific Studies, University of California, San Diego.