The atlas can help researchers understand why there is a late 20th century trend towards drier conditions with monsoon weakening over India and Southeast Asia.
“This will hopefully lead to more accurate monsoon forecasts,” principal investigator Edward Cook from Lamont Doherty Earth Observatory in Columbia University told Deccan Herald.
“This atlas should provide monsoon modellers with new insights into how and why the summer monsoon varies the way it does and also how to improve their models,” he added.
The reconstruction of monsoon history shed new lights on the fall of the Ming dynasty in China, the political reorganisation in Southeast Asia, the revolt in Vietnam against the French, and the collapse of the Khmer civilisation in Angkor Vat, the scientists reported in the journal Science on Friday.
The atlas reveals “fingerprints” of Asian monsoon on the Earth since 1300 AD and could be used in future to compare patterns of sea surface temperatures with monsoon precipitation and improve climate modelling for much of the world.
The four Asian mega-droughts are: the first one, between 638 and 1641 (during which the Ming dynasty fell in China); the second, between 1756 and 1758 (the Strange Parallel drought linked to South Asian churning); the third, between 1790 and 1796 (East India drought); and the last one, between 1876 and 1878 (the Late Victorian great drought).
The East India and the Late Victorian droughts coincided with two severe El Nino events and their impact was the most severe in India. While the first one had an impact of the East India Company's plans on Permanent Settlement, the second mega-drought led to the Great Famine or Madras Famine that killed thousands.
The famine affected South and Southwestern India — Madras, Mysore, Hyderabad, and Bombay — for two years. In its second year, the famine also spread north to the Central Provinces, the United Provinces and a small area in the Punjab.
“With the MADA (monsoon Asia drought atlas) we now have a much more complete record of past mega-droughts. Some of these, like the "Strange Parallels" drought in the mid-18th century and the Angkor droughts in the 14th and 15th centuries, were not previously known,” said Cook.
“The atlas will help scientists understand the cause of monsoon variability,” remarked Eugene R Wahl from the National Oceanic and Atmospheric Administration of the USA.
The atlas was prepared by extracting tree ring data from more than 300 locations in South Asia. As trees grow, they develop annual rings whose thickness reflects contemporary temperatures and rainfall.
Their reconstruction covers three key climatic events in the last millennium: the latter part of the Medieval Climatic Anomaly, the Little Ice Age (between 16th and 19th century), and the contemporary period of human-based climate change.
Asian mega-droughts, the researchers found, are as big in “magnitude and persistence” as the mega-droughts in the southwestern USA, which are linked to sea surface temperature anomalies in the Pacific.
