Summary of Abstract Submission

Abstract Submission No. IO50-05-0058PresentationKeynote

CURRENT DECREASING TREND OF THE INDIAN SUMMER MONSOON: ARE WE HEADING TOWARDS AN INDIAN MONSOON COLLAPSE?

B. N. Goswami*1

1 Pisharoty Chair Professor, MoES
Indian Institute of Science Education and Research, Pune, India

ABSTRACT :

The more frequent droughts over India in the last two decades in the backdrop ofthe significantweakening of Indian summer monsoonby 4% since 1940 is a major cause of concern for food and water security of the country. The large increasing trend of Indian Ocean (IO) sea surface temperature (SST) appears to be responsible for this weakening trend of the Indian monsoon by strong increase in the tropospheric temperature (TT) over the equatorial IO and thereby weakening the north-south gradient of the TT over the region. The weakening Indian summer monsoon (ISM), in turn, results in anomalous westerly anomaly in the equatorial IO leading to further increase in the SST over the region. This self-sustaining mechanism for increasing SST over IO and weakening ISM raises the question whether this air-sea interaction would lead to a runway decrease of the Indian monsoon.
Looking at past records of ISM rainfall, an analysis of ISM proxies in the past 1000 years indicates that such extended decreasing spell of ISM was not uncommon in the past. It also indicates the existence of a 50-80 year multi-decadal oscillation of ISM. Could the current decreasing trend of ISM be part of the natural 50-80 year oscillation? We show evidence that indicates the ensuing air-sea interactions leading to weakening monsoon and increasing IO SST is sowing the seed of its own destruction involving both the IO and the Pacific. The increasing convective activity in the eastern IO is leading to strengthening the easterlies in the western equatorial Pacific and pushing the Pacific Ocean to go towards a negative (La-Nina) phase of the ENSO multi-decadal oscillation. The negative phase of the ENSO multi-decadal oscillation, is then expected to take the Indian monsoon to the positive phase through the teleconnection outlined by Krishnamurthy and Goswami (2000). Therefore, we conclude that the Indian monsoon is expected to recover and IO SST stabilized in the next one decade or so.