- Why in News- India’s four-year run of great summer monsoon rainfall is likely to end this year, with the India Meteorological Department (IMD) forecasting a 4% shortfall in the coming season.
- Though still categorised as “normal”, it is — at 96% of the long period average (LPA) — at the lowest end of what the agency categorises as normal rainfall.
- The key factor believed to be playing spoilsport this year is the development of El Nino, a cyclical phenomenon of warming in the central Pacific that in six out of 10 years is linked to diminished rainfall in the country.
- Since 2019, India has been under the influence of the converse La Nina or a cooling in those regions, and therefore, getting substantial rainfall.
- The “normal” monsoon rainfall over India during June-September is 87 cm (considered 100% of the LPA), though this involves wide spatial variability.
- From 1951 to 2022, there have been 15 El Nino years, defined as a rise above 0.5 degrees Celsius in temperatures in the central, equatorial Pacific Ocean with nine of those years witnessing “below normal” rainfall.
- In 2015, the last “strong” El Nino year (>1.5 degrees Celsius rise), the monsoon rainfall fell by 14%.
- Experts say that while El Nino conditions are imminent, there are ameliorating factors that may blunt its impact.
- One, El Nino is only likely to begin to take root in the second half of the monsoon — August and September.
- The weather models also indicate the development of a “positive” phase of the Indian Ocean Dipole during these months and so, a somewhat reduced impact of the El Nino.
- IOD, or warmer temperatures in the Arabian Sea and hence more moisture and rainfall over India).
- Another factor that could blunt the El Nino is reduced snow cover in Eurasia, which is favourable for monsoon .
- In recent years, the IMD has started to place greater emphasis on the ‘dynamical’ monsoon forecast techniques where global atmospheric and ocean conditions are simulated on powerful supercomputers to forecast climate conditions.
- This is different from the traditional, statistical approach.
