According to local media reports, heavy rainfall has lashed parts of Bangladesh, with Feni and Chittagong among the hardest-hit areas. In Feni town, continuous overnight rain has submerged several key locations, causing widespread disruption.
The downpour is expected to continue over the next two to three days, raising concerns of further flooding.
Severe waterlogging has already been reported in residential areas, marketplaces, and major roads. Low-lying neighbourhoods such as Charipur and Rampura are underwater, significantly impacting daily life and mobility across the district.
While local experts attribute the worsening waterlogging in Feni to three primary factors -- unplanned urban development, inadequate drainage infrastructure, and a lack of regular maintenance -- I would like to offer an additional perspective on the ongoing flooding affecting Feni and other regions of Bangladesh, focusing on oceanic and atmospheric drivers.
The local assessments provide valuable insights from a micro-level urban planning standpoint; however, a broader, macro-level analysis is equally important.
Since rainfall -- particularly extreme rainfall -- is fundamentally influenced by ocean-atmosphere interactions, understanding these larger-scale climate dynamics is crucial to fully grasp the causes behind the current rainfall and flooding.
According to global climate prediction centers, El Niño–Southern Oscillation (ENSO)-neutral conditions persisted with a 74% probability during the June-August 2025 period. Looking further ahead, forecasts indicate a 46% chance of ENSO-neutral conditions continuing between November 2025 and January 2026, along with a 41% probability of La Niña developing. The likelihood of El Niño remains low, at less than 15%.
During the same period, the Indian Ocean Dipole (IOD) remained in a neutral phase. However, some climate models indicated a potential shift toward a negative IOD by late summer, which could enhance moisture inflow and increase rainfall over the Bay of Bengal region.
Additionally, reports from global climate centres noted that the Madden–Julian Oscillation (MJO) was in a weak and uncertain phase during May, limiting its immediate impact on regional weather patterns. However, projections suggested that if the MJO were to strengthen in the coming weeks, it could boost tropical convection, potentially leading to heavier rainfall and more active monsoon conditions over Bangladesh later in the season.
Recent developments have confirmed earlier projections regarding the Indian Ocean Dipole (IOD) and Madden-Julian Oscillation (MJO), both of which underwent significant shifts in June 2025. These changes contributed to widespread rainfall and the ongoing flooding across Bangladesh, while ENSO conditions remained neutral.
The IOD transitioned toward a negative phase, with the Dipole Mode Index (DMI) decreasing from +0.21°C in May to -0.06°C in June, signaling a gradual shift. Simultaneously, the MJO, which had been weak and disorganized in May, strengthened over the Bay of Bengal by mid-June. This resurgence enhanced monsoonal convection and sustained strong basin-wide circulation, both of which played a key role in the intense rainfall and resulting floods.
How does a negative iod cause heavy rainfall in bangladesh and surrounding areas?
When the IOD is in its negative phase, the eastern Indian Ocean near Indonesia, including the Bay of Bengal region, experiences warmer sea surface temperatures. This warming leads to:
- Increased evaporation: Warm ocean waters increase evaporation, adding more moisture into the atmosphere.
- Enhanced moisture transport: The warm waters boost convection and moisture inflow from the ocean to surrounding land areas, including Bangladesh, northeastern India, and parts of Southeast Asia.
- Strengthened monsoon: The extra moisture fuels stronger monsoon winds and heavier rainfall, especially during the June-September monsoon season.
As a result, a negative IOD often correlates with above-average rainfall and flooding risks in Bangladesh and nearby regions, as more moisture-laden air is pushed inland, leading to persistent and intense precipitation events.
How does an active mjo cause heavy rainfall in bangladesh?
An active MJO acts like a large-scale “rainmaker,” enhancing convection and moisture flow over the Bay of Bengal and South Asia, which often results in heavy rainfall and increased flooding risk in Bangladesh. It leads to:
- Increased rainfall: Enhanced convection brings more moisture, leading to heavier rainfall.
- Stronger monsoon winds: The MJO can intensify monsoon winds, directing more moisture toward Bangladesh.
- Atmospheric instability: The MJO can destabilize the atmosphere, making it more conducive to heavy rainfall events.
These factors collectively contribute to the heavy rainfall observed in Bangladesh during active MJO phases.
In summary, while various local and regional factors contributed to the 2025 floods in Bangladesh, ocean-atmosphere dynamics -- often referred to as "ocean weather" -- also played a significant role.
Despite Bangladesh’s high vulnerability to climate variability, localized research on key ocean-atmosphere phenomena -- such as the ENSO, including its eastern, central, and Modoki-like variants, the IOD, and the MJO -- remains limited, fragmented, and underdeveloped.
Bridging these critical knowledge gaps will require multidisciplinary collaboration, investment in advanced climate modeling infrastructure, and the integration of indigenous knowledge with global scientific understanding.
Strengthening research in these areas is essential for building Bangladesh’s climate resilience, supporting agricultural planning, and improving disaster risk reduction.
Institutions such as the Institute of Water Modelling (IWM) (iwmbd.org) and similar organizations are well-positioned to lead these efforts and help build a more climate-informed future for the country.
Dr Rashed Chowdhury is an Adjunct Faculty at Arizona State University (USA) and a Non-Resident Research Advisor for the “2024 Flood Project” at the Institute of Water Modelling, Bangladesh. (Email: [email protected]).
