Changing droughts and floods in the Bay of Bengal: Insights from high-resolution climate simulations

The Bay of Bengal region is critically important both climatically and socioeconomically. Its warm waters influence monsoon patterns, which are essential for sustaining agriculture across India, Bangladesh and Myanmar. However, the region is increasingly experiencing floods and prolonged droughts that disrupt water availability and crop production, threatening the livelihood of millions of people. These not only exacerbate food insecurity but also highlight the vulnerability of densely populated coastal areas to climate variability. Understanding the future dynamics makes the Bay of Bengal a crucial area for climate modelling.

To that purpose, we conducted five high-resolution simulations, each spanning 30 years, using the Weather Research and Forecasting (WRF) model under different Shared Socioeconomic Pathways (SSPs) and time periods. The spatial resolution of the domain is 5 km, with hourly outputs stored. The first simulation was run under present climate conditions (1981–2010). For the future, SSP2-4.5 and SSP5-8.5 scenarios were considered, and two distinct periods were simulated: mid-century (2031–2060) and end-of-century (2071–2100).   

The analysis of the Standardized Precipitation Evapotranspiration Index (SPEI) calculated over 6 and 24 months suggest important changes on both short- and long-duration droughts. The probability of short drought occurrence is quadrupled in some areas of central and east India under both scenarios, and tripled in some parts of the Ayeyarwady delta in Myanmar. The severity of the droughts will be exacerbated by the end of the century, particularly over central Myanmar and coastal areas of India in both scenarios. For the long term, SPEI-24 indicates that severe droughts will be found over mainland India under both SSPs. The droughts will intensify also along the western coast of Myanmar and the Ayeyarwady Delta in most of the periods, except for the latest period of SSP5-8.5.

Additionally, changes in flooding are being investigated through flood assessments using coupled HEC-HMS and HEC-RAS modeling over Myanmar. Preliminary findings suggest significant changes in flooding in the Ayeyarwady Delta by the end of the century, with an increase in severity, especially under the SSP5-8.5 scenario. Similarly, flooding is expected to intensify along the Ayeyarwady River from the confluence with the Chindwin River to Magway —covering most of the central dry zone— by the end of the century under SSP-8.5.

Changes in atmospheric dynamics and the monsoon seem to be playing a role in the occurrence of droughts, but further understanding of these connections is needed. Our results highlight emerging patterns of drought and flood risk that warrant closer examination, offering valuable insights for future hydroclimatic assessments and regional planning.