The El Niño-Southern Oscillation (ENSO) and seasonal flooding – Bangladesh

Summary

Although the El Niño-Southern Oscillation (ENSO) affects one-quarter of the globe to a significant extent, scientific research in Bangladesh relating to ENSO is just beginning. The prime objective of this paper is to provide an improved description of the ENSO-related flooding variability in Bangladesh. Information analyzed for this study includes: i) locally available Bangladesh rainfall and flood-affected area data, and ii) globally available precipitation, sea surface temperature (SST), and atmospheric circulation data.

The study revealed that Bangladesh climate – despite weak quantitative correspondence between the strength of ENSO and the rainfall anomaly – has particularly a strong relation when SOI (Southern Oscillation Index) extremes, negative SOIs for dry, and positive SOIs for wet. In the case of a moderate anomaly in the SOI, the index-climate relation appeared to be contradictory and, in particular, Bangladesh is wet during moderate El Niño years. Therefore, while the relation between SOI – rainfall in the upstream Ganges-Brahmaputra-Meghna (GBM) basins in India is strong, the same SOI – rainfall relationship offers limited applicability in the context of Bangladesh climate. So, understanding the broad-scale features of the Asian monsoon with especial emphasis to Bangladesh is essential. Further, the simultaneous development of SOI – rainfall relationship limits its use for seasonal forecasting in Bangladesh. Therefore, this study, in addition to examining the SOI – rainfall relationship, emphasizes the role of the warm/cold sea surface temperature (SST) in the tropical Pacific/Indian Ocean along with atmospheric circulation patterns for seasonal climate predictions in Bangladesh. It concludes that a close co-operation between the local institutions and those of International forecast centers would be essential for seasonal climate forecasting in Bangladesh.