Impacts of the Madden-Julian Oscillation (MJO) on rainfall in Sri Lanka

Abstract

The influence of the Madden Julian Oscillation (MJO) on rainfall in Sri Lanka (SL) is examined based on 30 years of daily station data from 1981-2010. Composites are constructed for each of the eight phases of the MJO defined with the Real-time Multivariate MJO (RMM) index, using daily rainfall data from 44 stations over SL for four climatic seasons and comparing to similar results from a satellite-based rainfall product. Composites of lower tropospheric wind and convective anomaly are also investigated in order to examine how the local rainfall anomalies are associated with large-scale circulations. The greatest impact of the MJO on rainfall over SL occurs in the Second Inter-Monsoon (SIM) and Southwest Monsoon (SWM) seasons. Enhanced rainfall generally occurs over SL during RMM phases 2 and 3 when the MJO convective envelop is located in the Indian Ocean and conversely suppressed rainfall in phases 6 and 7. This rainfall impact is due to the direct influence of the MJO’s tropical convective anomalies and associated low-level circulations in the vicinity of SL. In contrast, the MJO influence during the Northeast Monsoon (NEM) season is slightly less than during the SWM and SIM seasons as a result of the southward shift of the MJO convective envelop during boreal winter. Occurrence of extreme rainfall events is most frequent during phase 2 in First Inter-Monsoon (FIM) phases 2 and 3 in SWM, phases 1, 2 and 3 in SIM and phases 2 and 3 in NEM seasons. The analysis of this study provides a useful reference of when and where the MJO has significant impacts on rainfall as well as extreme rainfall events during four climatic seasons in SL. This information can be used along with accurately predicted MJO phase by dynamical or statistical models, to improve extended range forecasting in SL.

The Influence of Weather Patterns and the Madden‐Julian Oscillation on Extreme Precipitation Over Sri Lanka

“…The frequency of occurrence of extreme precipitation events in most clusters is enhanced in MJO phases 1-4 and suppressed in phases 5-8, in general agreement with previous studies (e.g., Jayawardena et al, 2020).…”

“…For example, many parts of the country received over 200 mm rainfall on 15 May 2016, causing more than 200 fatalities and about USD 2 billion in economic losses (Koralegedara et al, 2019;Samantha, 2018). Jayawardena et al (2020) found that rainfall in Sri Lanka is enhanced (suppressed) in phases 2-3 (6-7) of the Madden-Julian Oscillation (MJO), and the occurrence of extreme rainfall events is enhanced in MJO phases 2-3. Deoras et al (2021) found that low-pressure systems forming over southern parts of the Bay of Bengal during June-September produce substantial rainfall in Sri Lanka, and the frequency of these Abstract Sri Lanka is affected by extreme precipitation events every year, which cause floods, landslides and tremendous economic losses.…”

Intercomparison of gridded precipitation datasets for prospective hydrological applications in Sri Lanka

“…Based on the climate and soils and vegetation, the country is divided into three zones: dry, intermediate and wet (Figure 1) with highly variable climate conditions (Jayawardena et al ., 2020). Table 1 presents the details of the climate zones.…”

“…The overall annual average rainfall is estimated to be 1850 mm (Imbulana et al ., 2006). High spatial variability in rainfall amount is observed from coastal areas to central hills (Jayawardena et al ., 2020). A high influence of El Nino Southern Oscillation is observed in the climate of Sri Lanka, where the El Nino results an increase in rainfall in October to December and reduction in January to March and July to August and La Nina causing the opposite (Suppiah, 1997; Zubair et al ., 2008).…”

“…Sri Lanka is a small island nation in South Asia, which has many small river basins where devastating floods result in vast damage and losses almost every year (Askman et al ., 2018). The nation has tropical climate with four distinct monsoon seasons, which affect parts of the country during different times of the year (Jayawardena et al ., 2020). Economy of the country is highly dependent on agriculture, and due to its fair share of natural disasters, mainly floods and droughts, the nation faces many difficulties (De Silva and Kawasaki, 2018).…”