Climate researchers in Germany said Wednesday they had found a way to more accurately predict the Indian monsoon, which could help maximise the subcontinent's food and hydro-power supplies. Improved forecasts of when the heavy summer rains start and end could help millions of farmers plant crops at the right time, and allow energy providers to estimate when dams and reservoirs fill up, they said.
Global warming already affects monsoon stability and will make accurate forecasting ever more important, as deviations can spark droughts and floods, said the Potsdam Institute for Climate Impact Research (PIK). "The timing of Indian summer monsoons, on which the livelihoods of many millions of people depend, is likely becoming more erratic," said project leader Juergen Kurths. "This makes early and accurate forecasting ever more crucial."
The scientists said they had developed a novel prediction method based on a network analysis of regional weather data, and would propose their model to the Indian Meteorological Department. "We can predict the beginning of the Indian monsoon two weeks earlier, and the end of it even six weeks earlier than before - which is quite a breakthrough, given that for the farmers, every day counts," said Veronika Stolbova of PIK and Zurich University.
"We found that in North Pakistan and the Eastern Ghats, a mountain range close to the Indian Ocean, changes of temperatures and humidity mark a critical transition to monsoon," said Stolbova in a statement. Usually the focus has been on southern India's Kerala region, said Stolbova, lead author of the study published in the scientific journal the Geophysical Research Letters.
The team said it used an advanced mathematical approach called network analysis of complex non-linear systems, combined with subtle statistical analyses of the early warning signals for the monsoon onset and withdrawal. "These precursor phenomena are often buried by huge piles of weather data and hence get overlooked," said PIK guest scientist Elena Surovyatkina of the Russian Academy of Sciences' Space Research Institute.
Kurths said they had looked at the climate system "as a network, just like the social networks so many people are using in their everyday life". "On Facebook or Twitter, you can follow how news is spreading, one posting leading to many others. In the climate system, not people but geographical regions are communicating - admittedly in a quite complex way."
Like Facebook postings or tweets that get shared again and again, the scientists explained, temperature and humidity get transported from one place to another by atmospheric flows such as winds. Information about monsoon timing is key for Indian farmers, who usually grow all-important crops like rice, soybean and cotton during the June-September monsoon season.
The scientists said they had tested their method with historical monsoon data and achieved correct predictions in more than 70 percent of cases for the start of the monsoon, and in more than 80 percent for its withdrawal. The authors said their method could improve the time horizon of monsoon prediction compared to that now used in India - both during relatively normal times, and in years when the El Nino phenomenon affects the rainy season.