Bangladesh: Time to develop a reliable flood forecasting model
By Shafiqul Islam
Most of Bangladesh is located within the floodplains of three large river systems: the Ganges, Brahmaputra and Meghna (GBM), with over 90 percent of the basin area outside Bangladesh. Flood is thus a natural phenomenon here, and people have been living with floods for centuries. Yet, not all floods are created equal, so to speak, nor all floods lead to a flooding disaster.
The three major rivers—the Brahmaputra at Bahadurabad, the Ganges at Hardinge Bridge, and Meghna at Amilshad—contribute over 80 percent of the water flow into Bangladesh. Given that over 90 percent of the GBM river basin is outside Bangladesh, it is critical to know upstream rainfall conditions, as well as the expected water flow into Bangladesh, to develop an accurate flood forecasting system. For example, rainfall at the farthest part of the Ganges basin may take 20-25 days to reach the Hardinge Bridge, while rainfall in Bihar may take only a few days to arrive at the bridge. A real-time data sharing of rainfall and water flow conditions across three major rivers from upstream countries like India, China, and Nepal can significantly enhance the accuracy of flood forecasting within Bangladesh.
In reality, however, such data sharing is not common. It is not helpful to engage in endless conversations about the power and politics of data sharing. We need to act with the capacity and constraints we have. For example, with the increased availability of satellite data and global model predictions of rainfall, data sharing, although desirable and useful, may become less and less relevant with time. We need to invest in a different type of flood forecasting platform.
Often, it may not be the type of flood but the timing of flooding that creates disastrous consequences. For example, a flash flood in the Sylhet region in April may cause more damage to crops than a monsoon flood in Sylhet in July. Over the last 35 years, the Brahmaputra at Bahadurabad has crossed danger level a total of 29 times. Yet, not all 29 crossings had similar flooding in northern Bangladesh.
Information about other natural, societal, and infrastructural factors is essential to forecast whether a flood is likely to create disastrous flooding and to minimise the associated impact. Following the guidelines of the United Nations Office for Disaster Risk Reduction, an operational flood warning platform needs to include four components: I) risk knowledge, II) monitoring and warning, III) dissemination and communication, and IV) response capability. Just having a high-quality forecasting model is not enough to reduce the impact of flooding. Failures in minimising impacts usually come from the "communication" and "response capability" elements as well as from the lack of public and political awareness of "risk knowledge".