Bihar is probably one of the worst flood affected state of India, accounting for nearly 73.06 % of the total geographical area and 76% of the total population reeling constantly under threat of flood. It accounts for about 17% of the flood prone area and 22% of the flood prone population in India. Bihar’s vulnerability to floods is due to its very flat topography just downstream of the steep Himalayas, intense Monsoonal rains (more than 2,500mm/yr in the upstream areas and about 1,200 mm/yr in the State, 80% during the months of June-September), high sediment loads, high population density (1106 per sq.km), low-socio-economic development, inadequate water infrastructure to regulate flow (e.g. storage upstream in Nepal or designated detention areas). The rivers that cause much of the flooding include the Ganges and its tributaries such as Burhi Gandak, Gandak, Adhwara Group, Kamla, and Kosi from the Himalayas on its left bank and the lower reaches of the Sone and Punpun rivers on its right bank. In the years 1978, 1987, 1998, 2004 and 2007 Bihar witnessed high magnitudes of flood. The total area affected by floods has also increased during these years. Flood of 2004 demonstrates the severity of flood problem when a vast area of 23490 Sq Km was badly affected by the floods of Bagmati, Kamla & Adhwara groups of rivers causing loss of about 800 human lives.Flood situation during 2005 and 2006 remain normal but floods of 2007 is believed to be the worst flood in Bihar affecting 10 million population of state.


Bihar is definitely a disaster prone state. Like floods, drought is also recurring phenomena in state. The main reason for drought is monsoon onset and uneven distribution of rainfall, over most parts of Bihar including northern part which is prone to flood faces drought situations. Mostly regions south of river Ganga faces severe drought every year during kharif season and are more vulnerable. Till2015, in nine out of 15 years, about 70 % districts of the state witnessed drought like situation, triggered by failure of southwest monsoon. Also the frequency is showing increasing trend. In 2004 number of districts affected by famine were 19, further rose to 26 in 2009. In 2013, out of 38 districts 33 were declared drought-hit, followed by 16 disatricts in 2015. The pre-monsoon drought is more severe as compared to post monsoon season. The 10 Districts of Bihar that are worst affected by drought the most are kaimur, Buxar, Gaya, Nawada, Rohtas, Bhojpur, Jahanbad , Siwan, Gopalganj, Patna and Aurangabad .


According to seismic hazard map of India, Bihar lies in Sesimic Zone III, IV and V i.e as having high earthquake vulnerability with potential to cause very high degree of devastation. Districts such as Araria, Madhubani, Sitamarhi, Supaul and Darbhanga lie in Zone V. The south-western districts such as Aurangabad, Bhojpur, Rohtas, Nawada, Kaimur, Gaya and Jehanabad lie in Zone III. The remaining parts of Bihar, including Patna lie in Zone IV. In past, the state has witnessed earthquakes causing devastating effects on millions of life. The major being 1934 earthquake in which more than 10000 people lost their lives, followed by 1988 and 2011 earthquake, and the most recent being a powerful 2016 earthquake measuring 6.8 on Richter scale.