Revisiting the Length of the Monsoon Rainy Season (LRS) over Northeast India (NEI)

Name of the Speaker: Prof. B. N. Goswami

Title of the Seminar: Revisiting the Length of the Monsoon Rainy Season (LRS) over
Northeast India (NEI)

Date and Time: 20 October 2023 (Friday), 10:00 am

Online Platform: MS Teams (link to the video of the seminar)

About the Speaker: Prof. Goswami did his pre-university in 1966 and B.Sc. from Cotton College in 1969 and master’s in physics from Gauhati University in 1971. He did his Ph.D in Plasma Physics from PRL, Ahmedabad in 1976 and a two-year postdoc with Prof. Jule Charney, a.k.a the ‘Father of modern Meteorology’ at the MIT and a 3-year postdoc at the NASA/GSFC on monsoon modelling. He then joined IISc, Bangalore from 1985 to 2006, becoming Professor and Chair of the Centre for Atmospheric and Oceanic Science (CAOS). He then moved to the Indian Institute of Tropical Meteorology, Pune in 2006 and then lead the Indian Monsoon Mission Program to uplift Indian weather and climate prediction capability to be one of the best of the world. He has served on many National and International Committees and has been Visiting Research Faculty at the Princeton University and Maryland University. He has been Members of many National and International Committees and has several Awards to his name such as Shanti Swarup Bhatnagar Award, 1995, K.R. Ramanathan Prize by Indian National Science Academy, 2008, Fellow, The World Academy of Sciences, Fellow, Indian Academy of Sciences, Fellow, Indian National Science Academy, Fellow, National Academy of Sciences, India, Fellow, Indian Meteorological Society, National Award in Atmospheric Science and Technology, 2014 by the Ministry of Earth Sciences, K. R. Ramanathan Medal, Indian Geophysical Union, 2014, Life Time Achievement Award in Science and Technology by Government of Assam, 2018, SERB Distinguished Fellow Award, Department of Science and Technology, Govt. India, (2018-2023) and many more.

Abstract: An iconic feature of the Indian Summer Monsoon Rainfall (ISMR), a longer than June-September rainy season over the Northeast India (NEI) while a much shorter one over the northwest India is expected to be altered by climate change but an objective definition of the length of the monsoon rainy season (LRS) over the NEI is lacking. While the May rainfall over the NEI is larger than June rainfall over central India (CI), the Onset of monsoon over NEI is considered to take place by June 5 by IMD. Here, defining the LRS objectively over NEI, we show that that climatological onset over NEI takes place around 18th May and withdrawal around 15th October making the length of the rainy season ~155 days. We further show that the El Niño and Southern Oscillation (ENSO) is a primary driver of LRS while rainfall during LRS is poorly correlated with the ENSO. We also provide compelling evidence to establish that May rainfall is ‘monsoon rainfall’ and not ‘pre-monsoon’ rainfall as assumed by the community so far. Inclusion of May rainfall over NEI in the seasonal rainfall of All India monsoon rainfall has important implications on variability and predictability of India monsoon rainfall. In contrast to a significant decreasing trend of LRS and LRS-rainfall during the historical period, the projected LRS under SSP5-8.5 scenario continues to decrease while the LRS-rainfall acquires a significant increasing trend over NEI. A significant increase in impact of hydrological disasters is expected over NEI in future due to increasing intensity and frequency of extreme rain-events within a shorter rainy-season.

Date(s) - 20/10/2023
10:00 am - 11:30 am

Interdisciplinary Centre for Water Research (ICWaR) - IISc Bangalore