© S. Priyadarshini
Large volcanic eruptions offer an additional novel path for monsoon predictions and for anticipating the strength of seasonal rainfall in the Indian subcontinent, a new study1 by a team of Indian and German researchers says.
With nearly half of India’s cultivated area being rain-fed, accurate forecast of the seasonal summer monsoon rainfall is critical for the agrarian economy. Prediction of the monsoon rainfall over India is closely connected to the evolution El Niño/Southern Oscillation (ENSO) – a dominant climatic phenomenon in the tropical Pacific Ocean.
Year-to-year variations in the monsoon are tied to large-scale patterns of sea surface temperature and sea level pressure variations with the El Niño phenomenon. However, in the backdrop of global warming, "the ENSO-Indian Monsoon (ENSO-IM) relationship has weakened during the last few decades resulting in the worsening of accurate prediction of the monsoon," the study, which explored the impact of volcanoes on the El Niño-monsoon connection, says.
Large volcanic eruptions have the potential to couple the phases of the ENSO and monsoon oscillatory systems, says corresponding author Raghavan Krishnan of the Indian Institute of Tropical Meteorology (IITM) in Pune, India.
Ash, particulates and gases ejected by volcanoes enter the stratosphere and block the solar radiation reaching the Earth’s surface. "Less sunshine means less warmth and hence a change of temperature differences between the Northern and Southern hemisphere," says Krishnan. "The preferential cooling of the northern hemisphere induces an El Niño-like anomaly in the tropical Pacific Ocean and alters the large-scale precipitation dynamics."
The volcanically forced ENSO-IM coupling enhances the predictability of the monsoon due to a stronger coupling between the monsoon over large parts of South and South-East Asia and the El Niño phenomenon after an eruption, the report says.
Commenting on the study, Jayaraman Srinivasan, Chairman of the Divecha Centre for Climate Change at the Indian Institute of Science in Bengaluru says the impact of volcanoes on El Niño is a controversial subject because of errors in the estimate of total particulates ejected and their optical properties.
"It also depends upon where the volcano is located (tropics, mid-latitudes, or the poles) and winds that prevail during the eruption". Not all El Niños have an impact on the Indian monsoon and we are still trying to understand why,” he says.
References
1. Singh, M. et al. Fingerprint of volcanic forcing on the ENSO-Indian Monsoon coupling. Science Adv. (2020) doi: 10.1126/sciadv.aba8164
