ReliefWeb

Flash Floods are caused by heavy or excessive rainfall, or upstream flooding, in a short period of time over a relatively small area. In flash floods, water levels rise and fall rapidly with little or no advance warning. Typically, they occur in areas where the upstream basin topography is relatively steep and the concentration time of the basin is relatively short, such as the Haor Basin of the northern belt of Bangladesh (Sylhet, Sunamganj, Moulvibazar, Habiganj, Netrakona, Kishoreganj) (BWDB 2014; WMO 2003). Though, geographically, most of the haors are situated across six districts in the North-East of Bangladesh, there are as many as 423 small or large haors in Bangladesh. Flash floods are most common from April to July and in September-October (WMO 2003).

Flash flooding inundates the Haor Basin for an average of six months every year. During the monsoon season, the entire Haor region goes underwater and is transformed into floodplains for fresh water fishing. The high seasonality of the Haor-based economy forces local people to remain out of work for a considerable period time, and as a result, they suffer from food insecurity. It is the barrier to sustainable livelihood development.

The frequently encountered effects of widespread and prolonged flooding and waterlogging are disruption of traffic movement and normal life; damage of structures & infrastructure; destruction of vegetation and aquatic habitats; and loss of income potentials. Such disruption can lead the vulnerable population to become even more vulnerable.

The Haor Basin is estimated to be sinking at between 4 mm and 2.1 cm annually because of the down-thrusting under the Shillong massif. This sinking means that annual flooding will become more extensive and will be exacerbated by sea level rise (IFAD 2011). In 2012, an estimated 320,000 people out of 2.4 million were affected and in need of assistance due to early flash flooding in the Haor (JNA SE 2012).