Strengthening of Sri Lanka summer monsoon rainfall with rapid Arabian Sea warming

Abstract

Several studies have shown that rapid sea surface temperature (SST) warming in the tropical Indian Ocean (IO) significantly modulates the summer monsoon rainfall (SMR) over India. However, it remains unclear how the IO SST warming affects the SMR in Sri Lanka (SL). Therefore, based on observations and reanalysis data, this study investigates the impact of IO warming on SMR variability in the wet-zone of SL during 2001–2020. The results revealed that the SMR (May–September) in SL's wet zone is increasing and is associated with rapid SST warming in the Arabian Sea during the summer monsoon. Although it is reported that the SMR may decrease over India due to the weakening of land-sea thermal gradient in summer associated with IO warming, the rapid warming of the AS appears to enhance the SMR in the wet zone of SL. The warming of the AS during summer strengthened the low-level easterlies, favouring moisture convergence and convection over SL, which enhanced the SMR of the wet zone of SL.