<p>Researchers at the Indian Institute of Science (IISc) are working with findings from a 2018 study to further understand the impact of the El Nino Southern Oscillation (ENSO) on the Indian summer monsoon rainfall.</p>.<p>The study by Arindam Chakraborty, Professor at the Centre for Atmospheric and Oceanic Sciences, for the first time, quantified monsoon rainfall variations in India caused by the combined states of ENSO during winter and summer. The findings could also complement ongoing efforts to study climate over thousands of years, to improve seasonal rainfall predictions.</p>.<p>ENSO is a recurring climate pattern that comprises El Nino, which causes a rise in sea surface temperatures in the eastern tropical Pacific Ocean, La Nina, which leads to the cooling of these surfaces, and a neutral phase.</p>.<p>The study, of rainfall data over 144 years, found that La Nina in the previous winter reduces mean rainfall over the country by about 4%, even during ENSO-neutral summers. The preceding winter’s La Nina was found to have the strongest impact during the El Nino summer, reducing the rainfall by about 14.5%, and “increasing the possibility of severe drought”.</p>.<p>The western and southern regions were found to be more prone to reduced precipitation when the preceding winter had La Nina. These spatial variations caused by winter La Nina were reported for the first time.</p>.<p>“Models are being simulated to understand why these variations happen. The existing models have limitations and identifying causes of these complex patterns is difficult but this is an ongoing process. The findings are significant because they present us new ways to interpret monsoon rainfall,” Prof Chakraborty told DH.</p>.<p>The study used precipitation datasets from two sources – rain gauge-based precipitation recorded over 144 years, from 1871 to 2014, and India Meteorological Department records of daily precipitation averages, from 1901 to 2014.</p>.<p><strong>Probing the past</strong></p>.<p>Even with increasingly accurate data, monsoon rainfall in India comes with its share of complexities that make forecasting difficult, eminent climate scientist Prof J Srinivasan said. The distinguished scientist at the Divecha Centre for Climate Change at IISc said studying climate over thousands of years could help improve the understanding of India’s monsoon rainfall with all its climate change-driven variables, like warmer oceans.</p>.<p>“Machine Learning will have its applications but it demands huge amounts of data. The data from 150 years is good but not enough; it has already been analysed in different ways. Now, we are looking at the climate in India over the last 20,000 years,” he said.</p>.<p>Researchers have been using simulated models with proxy data – from ice cores and mineral deposits in caves, for instance – to track the evolution of climate over the last 21,000 years. “The good news is that here, our models could infer that monsoon rainfall in India was very low during the Ice Age (about 21,000 years ago). These findings will enable us to predict seasonal rainfall better,” Prof Srinivasan said.</p>
<p>Researchers at the Indian Institute of Science (IISc) are working with findings from a 2018 study to further understand the impact of the El Nino Southern Oscillation (ENSO) on the Indian summer monsoon rainfall.</p>.<p>The study by Arindam Chakraborty, Professor at the Centre for Atmospheric and Oceanic Sciences, for the first time, quantified monsoon rainfall variations in India caused by the combined states of ENSO during winter and summer. The findings could also complement ongoing efforts to study climate over thousands of years, to improve seasonal rainfall predictions.</p>.<p>ENSO is a recurring climate pattern that comprises El Nino, which causes a rise in sea surface temperatures in the eastern tropical Pacific Ocean, La Nina, which leads to the cooling of these surfaces, and a neutral phase.</p>.<p>The study, of rainfall data over 144 years, found that La Nina in the previous winter reduces mean rainfall over the country by about 4%, even during ENSO-neutral summers. The preceding winter’s La Nina was found to have the strongest impact during the El Nino summer, reducing the rainfall by about 14.5%, and “increasing the possibility of severe drought”.</p>.<p>The western and southern regions were found to be more prone to reduced precipitation when the preceding winter had La Nina. These spatial variations caused by winter La Nina were reported for the first time.</p>.<p>“Models are being simulated to understand why these variations happen. The existing models have limitations and identifying causes of these complex patterns is difficult but this is an ongoing process. The findings are significant because they present us new ways to interpret monsoon rainfall,” Prof Chakraborty told DH.</p>.<p>The study used precipitation datasets from two sources – rain gauge-based precipitation recorded over 144 years, from 1871 to 2014, and India Meteorological Department records of daily precipitation averages, from 1901 to 2014.</p>.<p><strong>Probing the past</strong></p>.<p>Even with increasingly accurate data, monsoon rainfall in India comes with its share of complexities that make forecasting difficult, eminent climate scientist Prof J Srinivasan said. The distinguished scientist at the Divecha Centre for Climate Change at IISc said studying climate over thousands of years could help improve the understanding of India’s monsoon rainfall with all its climate change-driven variables, like warmer oceans.</p>.<p>“Machine Learning will have its applications but it demands huge amounts of data. The data from 150 years is good but not enough; it has already been analysed in different ways. Now, we are looking at the climate in India over the last 20,000 years,” he said.</p>.<p>Researchers have been using simulated models with proxy data – from ice cores and mineral deposits in caves, for instance – to track the evolution of climate over the last 21,000 years. “The good news is that here, our models could infer that monsoon rainfall in India was very low during the Ice Age (about 21,000 years ago). These findings will enable us to predict seasonal rainfall better,” Prof Srinivasan said.</p>