Mega droughts in the monsoon area – University of Innsbruck
An international team of researchers, including geologist Christoph Spötl, was able to use stalactites to reconstruct in detail the monsoon of the last millennium in north-eastern India for the first time. Today’s wettest region on earth once suffered from several mega droughts with massive famines. The team not only confirms traditional chronicles, but also shows the potentially large dynamics of monsoon systems, the extent of which WILL improve even further as a result of anthropogenic climate change.
The state of Meghalaya in north-eastern India is considered to be the wettest region on earth with around 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 come, there will be no harvest. It is known from historical records and chronicles that there have been long-lasting droughts over the past few centuries, which have led to famine but also to political upheavals,” explains Christoph Spötl, head of the Quaternary research group at the Institute for Geology at the University of Innsbruck. Such an event has not been documented since instrumental measurements of meteorological data began in 1871. In the study with lead author Gayatri Kathayat from Xi’an Jiaotong University, which has now been published in the journal PNAS (Proceedings of the National Academy of Sciences), the team now presents a precise reconstruction of the precipitation development of the Indian monsoon over the last 1000 years.
Stalactites as a “history book”
The data for the Indian summer monsoon reconstruction was provided by stalactites from Mawmluh Cave in Meghalaya. “We use these cave deposits as a climate archive, because they store climate information layer by layer, sometimes far into the past, which allows us to leaf through it like a history book. We were able to find two ‘good’ stalagmites in this cave: They give us a glimpse into the development of the Indian monsoon precipitation over the last millennium with a very precise resolution down to years,” Spötl explains. To do this, 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: “The monsoon has been relatively constant since the recordings with measuring devices began. If we look further into the past, however, we see that in the past millennium there were frequent long-lasting periods of drought and thus the monsoon was almost completely absent.” The extreme events detected in the stalactites coincide conspicuously with historically documented droughts, famines and major geopolitical changes in India. “But our paleo data also show how dynamic monsoon systems can be on fast timescales. Since we know that extreme events are already increasing due to the climate change caused, massive floods are to be expected – in the long term, however, droughts may also be expected, which, as in the past, can last for several decades,” Spötl points out. “We therefore advocate incorporating these findings from the climate history of the world’s largest monsoon system both in future climate modeling and in political decisions on adaptation strategies.”
Publication:
Protracted Indian monsoon droughts of the past millennium and their societal impact.
Gayatri Kathayata, Ashish Sinhab, Sebastian Breitenbach, Liangcheng Tand, Christoph Spötl et al., PNAS 2022, Vol. 119
DOI: 10.1073/pnas.2207487119