Major revolts in ancient Egypt may have been triggered by volcanic eruptions that prevented the Nile from its usual summer flooding.

That’s according to research conducted by TCD and Yale University historians who examined evidence from ancient Egyptian writings during the Ptolemaic period, as well polar ice-core records and climate modelling.

The researchers believe that this research, published in Nature Communications can improve understanding of how societies respond to climate shocks.

Egypt’s Ptolemaic era, which ran from 305 BC to 30 BC is famed for its prosperity, cultural and material achievement, rulers such as Cleopatra, and was home to the great city of Alexandria.

The success of Egypt during this glorious period of its history was directly linked with the river Nile, and its annual summer flooding, which provided the water, and irrigation necessary to support the region’s thriving agriculture.

“It is very rare in science and history to have such strong and detailed evidence documenting how past societies responded to sudden hydroclimatic shocks,” said Dr Francis Ludlow, from the TCD School of Histories and Humanities, who jointly led the study.

“To fully understand how sudden environmental pressures could act to destabilise society, the historical context is key, and in this case included pressures from high levels of taxation and ethnic tensions that likely coalesced to trigger revolt at times of agricultural failures from insufficient floodwaters,” Dr Ludlow added.

The researchers were able to show that large volcanic eruptions disrupted the African summer monsoon and reduced Nile river flow. This helped to trigger economic and political instability, in particular to trigger revolts against Ptolemaic rule of Egypt and limiting that state’s ability to wage warfare.

The authors also provided evidence of further social stresses through the increased sales of family-held land following eruptions. This has been documented in the surviving records, and likely to have occurred because families were unable to meet state taxation demands after failed harvests.

The study, according to the authors, also has significant implications regarding how societies will respond to future climate change, and more specifically about how the nations that depend upon the summer flood waters of Nile might manage under the impact from the next big volcanic eruption.