New Delhi: As extreme rainfall events witness a steady rise in different regions of the world, a new research has shown that occurrence of such events are connected globally.
The new findings published in science journal Nature can help in improving global climate models to predict when and where extreme rainfall events will occur around the world. It focuses on South Central Asia, which includes major parts of north-western India.
“The results can help in predicting extreme rainfall and associated flash floods and landslides in northeast Pakistan, north India and Nepal, where there have been several such hazards in recent years, with devastating consequences," said lead author, Niklas Boers from the Potsdam Institute for Climate Impact Research, Germany, and Imperial College, London, who conducted the study.
The findings show that the extreme rainfall events in India have teleconnections with those in Europe and Africa and East Asia. For instance, extreme rain in Europe may at times precede extreme rainfall in India by around 4-5 days, without extreme rain in countries in between.
According to scientists, the patterns of these events are manifested through atmospheric waves called Rossby waves, which are carried through upper atmospheric jet streams. Rossby waves have been connected to regular rainfall, but this study is the first to connect them to extreme rainfall event patterns.
However, Indian scientists highlight that South Central Asia considered in this study covers mainly north-western states of India, which includes only a small part of the core monsoon region. Also, most of the extreme rainfall events associated with the Indian monsoon happen outside that region.
“Also, it does not mean that all extreme rains over India are linked to extremes elsewhere. Some of the recent extreme rains over India were attributed to a combination of remote and local factors such as surface temperatures over the Indian Ocean, land use-land cover changes and urbanization," said Roxy Mathew Koll, a scientist from the Indian Institute of Tropical Meteorology (IITM), Pune.
Scientists also highlight that on many occasions, extreme rainfall events in the core monsoon region or in the west coast region are associated with monsoon depressions or due to the interaction between monsoon flow and the topographic features.
“It is well known that the rain in the north-west region has strong links with ‘western disturbances’, which are also part of the Rossby wave train and it is fairly well predicted due to its nature of propagation. But, the study has shown strong robustness of that link," said Francis P A from the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad.
The study paves the way in providing some lead time for successful prediction of extreme rainfall events and understanding the connections between different monsoon systems.
“It also adds another piece to the puzzle on the monsoon extremes," says Koll, “It may be interesting to see if these teleconnections have changed over time due to rising temperatures and if those changes are reflected on extremes over India."
The scientists involved in the study had analyzed satellite data from the Tropical Rainfall Measuring Mission from 1998. Using a statistical measure that assesses connections even if the events did not occur at exactly the same time, the team examined occurrence of extreme rainfall events across the globe and determined how ‘synchronous’ these were.