The influence of weather patterns and the Madden-Julian Oscillation on extreme precipitation over Sri Lanka

Sri Lanka is affected by extreme precipitation events every year that cause floods, landslides, and tremendous economic losses. Unlike for other countries in South Asia such as India, there has been a limited investigation of weather patterns associated with extreme precipitation events in Sri Lanka. In this study, we use the ERA5 reanalysis dataset to understand the association between extreme precipitation events and 30 weather patterns, which were originally derived to represent the variability of the Indian climate during January–December 1979–2016. Furthermore, we analyse the modulation of extreme precipitation events by the Madden-Julian Oscillation (MJO). We also use the daily rainfall data from 51 meteorological stations in Sri Lanka to take some account of the observational uncertainty.

We find that weather patterns that are most common during the northeast monsoon (December–February) and second intermonsoon (October–November) seasons produce the highest number of extreme precipitation events. Moreover, extreme precipitation events occurring during these two seasons are more persistent than those during the southwest monsoon (May–September) and first intermonsoon (March–April) seasons. The frequency of extreme precipitation events is enhanced (suppressed) in MJO phases 1–4 (5–8) for most weather patterns. The results of this study could benefit meteorologists, hydrologists, and researchers in developing forecasting products based on the identification of these weather patterns and MJO phases in numerical weather prediction and the subseasonal-to-seasonal prediction models, envisaging improved disaster preparedness in Sri Lanka.