The flood situation in Bihar turned grim Sunday with the death of four people as around 18 lakh were affected in nine districts of the state, an official report said. Five rivers of the state are flowing above the danger level due to torrential rains in the catchment areas bordering Nepal, the report by the Disaster Management Department said. Chief Minister Nitish Kumar conducted an aerial survey of the flood-affected areas of several districts. A total of 17, 96, 535 population has been affected by flood waters in 55 blocks of nine districts. The Patna Meteorological Centre has forecast rain with thunderstorm at many places in Bihar in the next four days.