Research team members Amy Hessl (top picture) and Neil Pederson study Siberian pine trees in Mongolia to reconstruct a year-by-year record of soil moisture over the past 1,112 years

New Delhi, March 10: A 15-year period of unusually high rainfall in Mongolia fuelled Genghis Khan’s conquest spree across Asia in the early 13th century, planting the seeds for India’s Mughal dynasty some 300 years later, a new study suggests.

American and Mongolian scientists have challenged suggestions by some historians that prolonged droughts may have stirred the Mongols, led by Genghis, to expand their territory and establish “the largest contiguous land empire in the planet’s history”.

For the first time, the researchers have reconstructed a year-by-year record of soil moisture, an indicator of rainfall, at a site in Mongolia over the past 1,112 years.

They have found that the period from AD 1211 to 1225 was persistently wet, though sandwiched between dry periods.

This period coincides with the Mongol expansion under Genghis from AD 1206 to 1227, which influenced the history of central Asia, Russia and India.

Babur, who established the Mughal empire in India after defeating Ibrahim Lodi in the first battle of Panipat in 1526, was --- through his mother --- a descendant of Genghis.

“This prolonged period of wet weather was a big surprise --- a really unusual occurrence,” Neil Pederson, a scientist at Columbia University in New York and a member of the research team, told The Telegraph over the phone.

Pederson and his colleagues believe that the wet weather favoured increased pastoral production, political centralisation, and military mobilisation.

The wet conditions allowed the Mongol leadership to concentrate political and military power in designated localities, which, the scientists say, was a “necessary and important factor” in the successful mobilisation of nomadic power used in Genghis’s conquests.

The researchers published their findings today in the journal Proceedings of the National Academy of Sciences.

The US-Mongolian research team examined a set of 107 Siberian pine trees in central Mongolia. These trees’ trunks contain year-by-year signatures of water ---- a measure of soil moisture or levels of rainfall or snow in the environment.

Their study showed an extended drought between AD 900 and 964, and extremely dry periods from AD 1115 to 1139, and 1180 to 1190. But the period from 1211 to 1225 was persistently wet ---- wetter on average than any period since then.

Historical records indicate that Genghis “reconstituted” his army and government into a strong, unified central command. Such a transformation, the scientists said, would have needed a concentration of resources that only wet weather could sustain in a pastoral land.

A higher productivity of the steppes would have favoured large concentrations of people and the formation of the army necessary for the invasions across central Asia.

“All empires require surplus concentrated energy,” Amy Hessl, a geographer at West Virginia University and member of the research team, told this newspaper via email.

“We now have a hypothesis about where this energy came from for the Mongols.”

The researchers said their findings show how unusual climatic events can significantly affect societies in semi-arid regions.

Pederson said it was not clear yet what climatic factors led to Mongolia’s 15-year wet period in the early 13th century.

The pine tree findings combined with recent meteorological observations suggest that a drought in central Mongolia between 1999 and 2002 was the hottest in the past 1,112 years, and comparable only to the drought in the 1180s.