ABSTRACT
Bangladesh lies in the delta of three large rivers - the Ganges, Brahmaputra and Meghna (GBM), which is often termed as a “land of rivers and water.” With a complex network of 230 rivers, including 57 cross boundary rivers, about 92.5% of the 175 million hectares (mha) of combined basin area of the GBM Rivers (Fig. 5.1) is beyond the boundary of Bangladesh and is located in China, Nepal, India and Bhutan. Therefore, Bangladesh acts as a drainage outlet for the cross-border runoff. More than 90% of the annual runoff is generated outside of Bangladesh. However, there is a high seasonal difference in the availability of water. For example, for the Ganges River, the ratio of dry and monsoon runoff is 1:6 (Fig. 5.2). This illustrates that Bangladesh has an abundance of water in the monsoon while the country still faces surface water scarcity in the dry season. Irrigated agriculture is highly dependent on dry season surface water availability. On average, annually floods engulf roughly 20.5% of the area of the country, or about 3.03 mha (Mirza, 2003). In extreme cases, floods may inundate about 70% of Bangladesh, as it occurred during the floods of 1988 and 1998 (Ahmed and Mirza, 2000). Hydrological droughts are very common in the rivers of Bangladesh.
