There's an interesting piece in The Economist about the link between rainfall and the rise and fall of Roman emperors.
One such lesson is how drought affected the stability of the Roman empire 1,500 years ago. In a new paper published in Economics Letters, Cornelius Christian of Brock University and Liam Elbourne of St Francis Xavier University identify a strong association between rainfall patterns and the duration in power of Roman emperors. The academics hypothesise that lower precipitation reduced crop yields, leading to food shortages and eventually starvation for soldiers stationed at the empire’s frontiers. As a result, troops were more likely to stage mutinies and assassinate their emperor.
The data, collected from oak tree rings, shows hungry troops peaking in revolts around The Gordian dynasty from 235 AD to 285. Invasions and the economic plight brought on by droughts were also contributors.
The academics combine data on assassinations—some 25 emperors were assassinated, roughly one-fifth of the total—with precipitation data collected from rainfall-sensitive oak-tree rings across the Roman frontier in France and eastern Germany.
Today's natural disasters in California, Greece, and Japan due to heatwaves may not lead to overthrows, but they don't augur well either.
It might be easy to dismiss the lessons from 1,500 years ago. Ancient Rome had little ability to store grain for long periods or irrigate crops. Yet, to this day, dictators rely on an obedient army to retain power. And more broadly, it has been long established that adverse weather causes economic shocks that lead to unrest, and even to civil war.