Climate-related megadroughts built the foundation for the collapse of the Neo-Assyrian Empire (912 to 609 BCE), the largest and most powerful empire of its time, a new study published in the journal Science Advances suggests.

Based in the floodplain of the Tigris River in ancient northern Mesopotamia, now northern Iraq, the Neo-Assyrian Empire emerged during the 10th century BCE from the remnants of the Middle Assyrian Kingdom.

Over the course of the next two centuries, the state expanded rapidly through military campaigns and forced taxation to become the superpower of the Near East.

At its height (670 BCE), the empire stretched from Central Anatolia in the north to the Mediterranean and Egypt in the west, and eastward to the Persian Gulf and western Iran.

However, the empire plummeted from its zenith to complete political collapse (615 to 609 BCE) in just six decades.

“Previous explanations for the empire’s collapse have focused on political instability and wars,” said lead author Dr. Ashish Sinha of California State University and colleagues.

“The role of climate change was largely ignored, in part because of a lack of high-resolution paleoclimate records from the region.”

In the study, the researchers gathered oxygen and carbon isotopic data from two stalagmites found in Kuna Ba Cave in northern Iraq, located 217.5 miles (300 km) southeast of the ancient city of Nineveh, which provide a precisely dated record of precipitation over the last 4,000 years.

“Our team analyzed drip water that got fossilized in two stalagmites in Kuna Ba Cave in northern Iraq,” said co-author Dr. Adam Schneider, a scientist in the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder.

“Because the oxygen and carbon isotope composition in different layers of the cave formations can be used to infer changes in precipitation at a high temporal resolution, we get a much better proxy than anything else we had previously.”

“And because the isotope record went all the way up to 2007, we were able to correlate the stable carbon and oxygen isotope ratios with modern instrumental climate information from the region.”

The records indicate that the interval between 850 and 740 BCE, when the Neo-Assyrian Empire was at its zenith, was one of the wettest periods in 4,000 years, with precipitation levels during the cool season 15 to 30% higher than during the modern 1980-2007 period.

However, the records also suggest that cool season precipitation during a 7th century BCE megadrought may have fallen below the level required for productive farming.

“Since the empire was highly dependent on agriculture, the megadrought would have likely exacerbated political unrest and may have encouraged invading armies that ultimately led to Assyrian collapse,” the study authors said.

“Our data suggest that the recent multi-year droughts, if they were to continue over a century, would constitute the worst episodes of regional drought in the last four millennia.”

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Ashish Sinha et al. 2019. Role of climate in the rise and fall of the Neo-Assyrian Empire. Science Advances 5 (11): eaax6656; doi: 10.1126/sciadv.aax6656