Abstract
The Indian Ocean Dipole (IOD) represents a significant driver of ocean-atmosphere coupled phenomena over the equatorial Indian Ocean (IO), exerting a strong influence on the inter-annual rainfall variability of Sri Lanka. However, the nature of the relationship between the IOD and Sri Lanka rainfall has undergone secular fluctuations over the past decades. Consequently, our study provides an in-depth analysis of the evolving relationship between the IOD and rainfall over the wet zone of Sri Lanka during the IOD peak fall, utilising reanalysis datasets from 1940 to 2020. It has been demonstrated that there is a weak and insignificant correlation between the IOD and rainfall over the wet zone of Sri Lanka during the pre-1980s. On the other hand, a strong and significant correlation was observed during the post-1980s. Furthermore, we found that positive IOD warming was higher in the post-1980s compared to the pre-1980s. This was attributed to strong walker circulation and, as a result, strong moisture convergence and convection over the western IO, which led to an enhanced relationship between rainfall over the wet zone of Sri Lanka and IOD. Thus, this study highlights how ocean-atmosphere changes in the tropical IO have contributed to strengthening the IOD- Sri Lanka rainfall relationship over recent decades and could be valuable for seasonal prediction in Sri Lanka.