Work

The relationship between equatorial wave interaction and heavy rainfall in Southeast Asia

Year: 2026

Type: article

Abstract: Equatorial waves are a driver of heavy rainfall events in Southeast (SE) Asia. These heavy rainfall events can be very damaging, resulting in landslides and flooding, but remain challenging to predict. Previous studies have demonstrated the role single equatorial waves play in heavy rainfall and the usefulness of this information in aiding forecasting. Less is known about the impacts when multiple equatorial waves co‐occur. Here, dynamically identified equatorial waves are used to construct a “compound” equatorial wave phase space to explore statistically how different combinations of the phases of Kelvin, equatorial Rossby, and westward‐moving mixed Rossby‐gravity (WMRG) waves are related to the intensity of precipitation in the SE Asia region. A demonstration of the methodology focuses on heavy rainfall in boreal winter in Peninsular Malaysia in relation to Kelvin and WMRG co‐occurrence. We show that heavy rainfall is significantly increased in Peninsular Malaysia during coincident Kelvin and WMRG waves, with heavy rainfall probability increased by up to seven times relative to climatology, compared with twice when activity from only one wave type is considered. Other regions profoundly impacted by wave co‐occurrence include the South Philippines, Sumatra, and Borneo; rainfall in 14 of the 15 regions examined showed significant relationships between heavy rainfall and compound wave occurrence. Moreover, it is found that in some cases the occurrence of both waves together, rather than a single wave alone, is a requirement for increased heavy rainfall probability. A table summarising the findings for all individual regions of SE Asia is produced and can aid forecasters in forecasting extreme weather events.

Source: Quarterly Journal of the Royal Meteorological Society

DOI: 10.1002/qj.70213