Equatorial Convectively Coupled Waves and Indonesia Floods

The floods in Indonesia account for over 30% of natural disasters with significant socioeconomic effects. The prediction of the floods is this region is usually based on seasonal and intraseasonal variability such as monsoon or Madden Julian Oscillation. We show that that severe weather conditions related to flooding are primarily due to the equatorially trapped waves and their interaction with local variability. To examine the relationship between the floods and equatorial waves data bases of floods based on local newspaper reports, social media (twitter) were developed and compared with the flood reporting by Indonesian government agencies as well as Kelvin wave data bases created in the course of our previous work. We show that depending on the position of an island the floods can be primarily related to Kelvin waves, Rossby waves or interaction between these modes and local diurnal variability. While in some cases the equatorial waves responsible for flooding can be related to the active phase of intraseasonal variability, the impact of the convectively coupled waves outside of the MJO envelope can also produce severe precipitation events, leading to floods. The implication of these findings to modeling and forecasting in the Maritime Continent are discussed.