When a drought makes the wells run dry and the crops wither in the field, what can you do? Ask a dragon for help, was the traditional solution in China around the year AD 1000. It seemed to work. In Murcia, Spain, for seven centuries, the Catholic Church has held special prayers. And rain tends to follow.
No wonder, says economist at Yale University. These 鈥渞ain-making鈥� rituals appear effective thanks to how rainy and dry days alternate in those places. In regions where this pattern is different, people tend not to bother invoking supernatural help.
The crucial difference is that in places like Murcia, precipitation becomes more likely with every day it doesn鈥檛 rain. So if there is a long dry spell and a religious leader takes action, there is a good chance that the weather will turn soon after.
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And if it doesn鈥檛, a follow-up ritual some days or weeks later will have an even better chance of seeming to provide relief. In China, the temple of a deity unwilling to bring rain could be desecrated. In Murcia, special masses are followed up by processions.
Esp铆n-S谩nchez and his colleagues compared reports on the customs of 1290 ethnic groups and detailed climate data from where they live, or lived. Among groups with a non-increasing chance of rain, they found, 30 per cent had a rain-making ritual. For groups where it does increase, this was 44 per cent.
The chance of rain after some number of dry days depends on things like feedback between moisture in soil and in air, and the time of year. 鈥淭he central idea, from a statistical perspective, is plausible,鈥� says at the Hamburg University of Technology in Germany, who was not involved with the study.
For a rising probability, he says, there are two distinct mechanisms. 鈥淥ne is true duration dependence: that is, the longer the dry spell lasts, the more likely it is to end. The other is seasonal anticipation: that is, rituals are performed near the end of the dry season, when rainfall would soon become more likely anyway. Both can make rain-making appear successful.鈥�
Esp铆n-S谩nchez also built a mathematical model describing how people will adjust their trust in rituals and in religious leaders based on what happens. It allows for both strategic timing of rituals by savvy priests and pure luck. In both cases, he says, priests that choose the moment shortly before the rains return are more likely to keep their jobs. 鈥淎nd that religion, or that ritual, is more likely to survive,鈥� he says.
The study addresses an important gap in the study of religion, Esp铆n-S谩nchez says, which is the origin of beliefs.聽鈥淔or belief in rituals to make rain, we have a credible mechanism of why this type of belief exists in some places and not in others.鈥�
That sounds right to at the University of Macau. He recently published a study on rain-making in China, which emphasised the role of confirmation bias, where people are more likely to recall and disseminate stories of rain-making successes. 鈥淚f [Esp铆n-S谩nchez鈥檚] results are real, then I might have underestimated the possibility that these rituals may be, in a sense, objectively effective,鈥� he says.
Esp铆n-S谩nchez thinks his model could be applied to rituals for other hardships, 鈥渓ike certain epidemics or diseases that have a similar pattern: sufficiently complex that you cannot really see that it鈥檚 just going to go away on its own, but sufficiently simple that doing something looks like you鈥檙e curing the illness鈥�.
Quarterly Journal of Economics
