The Ganges-Brahmaputra-Meghna (GBM) river system, one of the world’s largest freshwater outflows, combines the Himalayan Ganges and Brahmaputra rivers with the non-Himalayan Meghna. This forms the vast Ganges-Brahmaputra Delta, a network of active and fading channels.
The rivers are influenced by seasonal monsoon rains, with the Brahmaputra traveling from Tibet through India before entering Bangladesh, and the Ganges flowing from India into Bangladesh. Most of the runoff comes from rainfall in the river basins outside Bangladesh. Heavy monsoon rains can cause flooding in Bangladesh, although local rainfall can sometimes exacerbate flooding.
Bangladesh relies on seasonal floods to grow its crops, but the timing and severity of these floods can be unpredictable. This unpredictability often disrupts farming and impacts many lives. To address this, better understanding and forecasting seasonal climate patterns and floods are essential, along with improved local use of this information.
Research on seasonal flooding in Bangladesh is still developing. Notably, Chowdhury and Ward (2004) found that stream flows in major rivers like the Ganges, Brahmaputra, and Meghna are closely tied to rainfall in their upper catchments in India, with about a one-month delay. Their findings indicate that real-time rainfall data from these upstream areas makes it possible to forecast river flows in Bangladesh with reasonable accuracy for up to three months, especially for the Ganges and Brahmaputra rivers.
Continuing from earlier research on seasonal forecasting, Chowdhury (2003) found that while the direct relationship between ENSO strength and rainfall anomalies in Bangladesh is weak, the climate does show a strong connection with extremes in the Southern Oscillation Index (SOI). Specifically, negative SOIs (associated with El Niño) tend to bring dry conditions, while positive SOIs (linked to La Niña) are typically associated with wetter conditions.
Chowdhury emphasized the importance of sea surface temperatures (SST) and atmospheric circulation patterns in the tropical Pacific and Indian Oceans for making seasonal climate predictions in Bangladesh. Furthermore, Chowdhury and Ward (2004) concluded that stream-flow forecasts in Bangladesh could be improved by considering unusually warm or cold SSTs in the tropics. Their work suggests that understanding these temperature patterns can enhance the accuracy of river flow predictions in the region.
By incorporating predictable climate patterns into flood forecasts and public preparedness efforts, we can enhance our ability to respond to flooding
This article aims to shed light on how to develop a seasonal forecast for flooding in Bangladesh. We explored how changes in tropical sea surface temperatures (SSTs) and general circulation models (GCMs) relate to flooding patterns in the region. Our goal was to examine how seasonal flooding in Bangladesh can be predicted based on:
- Oceanic and atmospheric changes in large-scale climate patterns, particularly in the tropical Pacific
- Precipitation forecasts from GCMs, which model how climate patterns influence weather
We also developed a statistical model to improve our understanding and prediction of flood patterns, with the goal of offering forecasts several months in advance. Our findings indicate that we can predict flood areas (FA) based on SSTs. The accuracy of these predictions improves further when we include data on rainfall and stream flows from Bangladesh.
Engineering solutions to flooding in Bangladesh would require significant time and investment, which may not be sustainable. Instead, improving our flood forecasting and warning systems using seasonal climate information could offer better planning and decision-making options for water management.
By incorporating predictable climate patterns into flood forecasts and public preparedness efforts, we can enhance our ability to respond to flooding. Moreover, the benefits of using seasonal climate information extend beyond just preparing for floods -- they can also impact regions beyond Bangladesh.
Md Rashed Chowdhury is Adjunct Professor in the School of Sustainable Engineering and the Built Environment of Arizona State University.
