The role of North West Equatorial Indian Ocean in modulating the variability of southwest monsoon rainfall over Kerala in a climate change perspective

摘要

The alarming rate of abrupt change in weather parameters, especially rainfall and temperature, is a cause of major concern not only for the scientific community but also for the lives of common people living in a country like India. A broad picture of climate change is not sufficient to carry out an impact assessment on a regional scale. Recent news on the occurrence of floods on a regional scale over India throws an urgent need to look at the patterns of changes in rainfall on a more regional scale. Kerala, the southwestern state of the Indian peninsula, is known to be the gateway of monsoon for the summer monsoon season to the mainland. This study is evaluating the causes of the recent variability in the rainfall pattern over Kerala during the southwest monsoon season. It is found that the Kerala rainfall is decreasing at the rate of 3 mm/year for the past 100 years, with an abrupt decrease of 6.7 mm/year after 1960. The causes of such a decrease are a point of discussion in this study. It is found that the ocean parameters such as sea surface temperature, ocean heat content and ocean heat fluxes are increasing at an alarming rate in the recent decade over the North West Equatorial Indian Ocean, including the Arabian sea. The pattern of the Findlater jet and the ocean response clearly identifies the North West Equatorial Indian Ocean as a hot spot which creates maximum variability in the southwest monsoon dynamics.