CHENNAI: The Indian Institute of Technology Madras (IIT-M) and Gauhati University have developed a new method to distinguish transient local rain spells from the establishment of the larger monsoon system.
The study, published in the Journal of Climate, uses a climate-network approach to identify large-scale monsoon onset at individual locations by tracking how clusters of local rainfall onsets across India grow and connect into a larger system.
The method could complement conventional monsoon definitions and provide useful information for decisions on sowing, water resources, food security and flood preparedness.
“The monsoon’s arrival at a location is not necessarily the first rainfall experienced there,” said Prof R.I. Sujith, Head of the Centre of Excellence for Studying Critical Transitions in Complex Systems, IIT-M.
The researchers define large-scale onset as the point when local rainfall becomes part of the largest interconnected cluster of rainfall onsets. This indicates that the rainfall has become embedded in the broader monsoon system rather than being caused by a temporary local weather event.
The researchers treated geographical locations as nodes in a climate network and tracked how rainfall-onset clusters grew and moved across the country.
Using 84 years of rainfall data, the researchers found that climatologically, large-scale onset occurs around May 15 over northeast India and June 9 over the Indian peninsula.
Prof B.N. Goswami of Gauhati University said the method was intended to complement, rather than replace, conventional operational definitions.
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