• Scientists have developed a new tool for objectively defining the onset and demise of the Indian Summer Monsoon – a colossal weather system that affects millions of people annually.
• The researchers from Florida State University in the US developed a method that uses rainfall rates to mark the span of the Indian Summer Monsoon (ISM) at any given location throughout the affected region.
• For generations, scientists have struggled to produce a model for reliably defining the duration of the monsoon. The researchers said that no existing system has allowed researchers to reliably define the parameters of the season at this fine a scale.
• Current weather forecasting and monitoring protocols focus attention on monsoon onset at one location-specifically the state of Kerala in the southwest corner of the country-and extrapolate for the rest of the region.
• The lack of a clear, granular and objective benchmark for ISM onset and demise for all areas of the country has been a longtime source of consternation for people, researchers said.
• In some parts of the country, the torrents of rain that characterise monsoon season account for more than 90 per cent of the total annual precipitation, they said.
• Researchers said that many rhythms of Indian political and agricultural life can be destabilised by dubious or false claims of monsoon onset.
• The new system, which ties the onset of the monsoon to location-specific rainfall thresholds works well. 
• Up until now, regional meteorological departments have relied on their own ad hoc criteria for determining ISM onset, which can often lead to contradicting claims.
• A more inclusive method will allow officials and researchers throughout the country to define the monsoon season using a standardised system that, through rigorous testing, has been shown to capture ISM evolution comprehensively.
• The system has been tested for 105 years of available data, and this criterion has not failed once for any location over India.

Source:TH