An international team of researchers with the participation of Innsbruck geologist Christoph Spötl was able to reconstruct the monsoon of the last millennium in northeastern India in detail for the first time using dripstones. The region with the highest precipitation on earth today once suffered several megadroughts with massive famines. Thus, the team not only confirms traditional chronicles, but also shows the potentially large dynamics of monsoon systems, the extent of which will be further intensified by anthropogenic climate change in the future.
The state of Meghalaya in northeastern India is considered the region with the highest rainfall on earth, with about 11 meters of precipitation per year. The enormous amounts of rain are mainly caused by the Indian summer monsoon, which comes from the sea and hits the Himalayan mountains in this area and rains out. "However, if this monsoon does not occur, there is no harvest. It is known from historical records and chronicles that there have been prolonged droughts again and again in the past centuries, which led to famines but also repeatedly to political upheavals," explains Christoph Spötl, head of the Quaternary Research Group at the Institute of Geology at the University of Innsbruck. Since the beginning of instrumental measurement of meteorological data in 1871, however, such an event has not been documented. In the study now published in the journal PNAS (Proceedings of the National Academy of Sciences) with lead author Gayatri Kathayat from Xi’an Jiaotong University, the team now presents a precise reconstruction of the precipitation development of the Indian monsoon over the last 1000 years.
Dripstones as a "history bookThe data for the reconstruction of the Indian summer monsoon was provided by stalactites from Mawmluh Cave in Meghalaya. "We use these cave deposits as a climate archive, as they store layer upon layer of climate information until sometimes very far into the past, allowing us to leaf through them like a history book. In this cave we were able to find two very ’good’ stalagmites: They allowed us to look into the development of Indian monsoon precipitation over the last millennium with a very precise resolution down to individual years," clarifies Spötl. For this purpose, the researchers* determine oxygen isotope data from the cave deposits, which can be "translated" into precipitation amounts. The results show a very dynamic picture, as Christoph Spötl explains: "Since the beginning of recordings with measuring instruments, the monsoon has been relatively constant. However, if we look further into the past, we see that in the last millennium there were often long-lasting droughts and thus the monsoon was almost completely absent." The extreme events detected in the stalactites strikingly coincide with historically documented droughts, famines and major geopolitical changes in India. "But our paleo data also show how dynamic monsoon systems can be on longer time scales. Since we know that extreme events are already becoming more frequent due to human-induced climate change, we can expect massive floods - but possibly also droughts in the long term, which can last for several decades, as in the past," Spötl points out. "We therefore advocate that these findings from the climate history of the world’s largest monsoon system be incorporated both into future climate modeling and into political decisions for adaptation strategies."
Quaternary Research Group at the Institute of Geology, University of Innsbruc k
Protracted Indian Monsoon droughts of the past millennium and their societal impacts.
Gayatri Kathayata, Ashish Sinhab, Sebastian Breitenbach, Liangcheng Tand, Christoph Spötl et al, PNAS 2022, Vol. 119.