Modulation of flood events in Indonesia by seasons, MJO, and la Nina

Floods in Indonesia are often triggered by heavy rainfall with a long duration. Such heavy rainfall was influenced by several factors include seasons, Madden-Julian oscillation (MJO), and La Nina. The number of flood events in Indonesia in term of seasons, MJO, and La Nina has been observed from the Indonesian National Board for Disaster Management (BNPB) data from 2008 to 2020. Flood events in Indonesia during the 13-year observation showed the increase of annual trend in accordance with the global disasters trend. Floods events showed a significant seasonal variation with maximum number of occurence during January and February and minimum during August, coincided with the monthly rainfall pattern concerning the monsoon seasons in Indonesia. Furthermore, the MJO strongly modulated the number of flooding in Indonesia, where the flood occurence during strong MJO is more than twofold compared to weak MJO. The peak number of flood events during strong MJO was observed in 3, 4, 5 phases. In addition, La Nina modulated the number of flood events more significantly in the wet season, while in the dry season, La Nina effect was not significant compared to seasonal variation.