Climate of Bihar in the south China sea. The maximum frequency of the tropical cyclones in Bihar is during September–November especially during the asterism called hathiya. These cyclones are essential for the maturing of paddy, and are required for the moistening of the soil for the cultivation of rabi crops. Bihar is India's most flood-prone State, with 76% of the population in the north Bihar living under the recurring threat of flood devastation. According to some historical data, 16.5% of the total flood affected area in India is located in Bihar while 22.1% of the flood affected population in India lives in Bihar.
Bihar County was established between 1020 and 1050, most probably by Stephen I, the first king of Hungary, or possibly by his successor, Peter. According to a version of a royal charter, issued in 1203, mentioned that "the whole Bihar County" was located partly around Bihar and partly around Zaránd (now Zărand in Romania), suggesting that Bihar County had originally included Zaránd County, or at least its territories north of the river Fehér-Körös. An other version of the same charter also mentioned Békés besides Bihar and Zaránd, implying that Bihar County had also included the lands which developed into the separate Békés