Rainfall variability and its impact on change of cropping systems in Bihar

The mean annual rainfall of 19 years (1989–2008) of Bihar is 1138.2mm with standard deviation 158.6 mm and coefficient of variation 14%. Although Bihar falls under high rainfall region with recurrent floods but occurrence of droughts during monsoon season is also a serious concern. In present study, the variability and trends of annual and monthly monsoonal rainfall for all the districts of Bihar have been analyzed and due to change in rainfall, the district-wise change in area of rice, wheat and maize has also been evaluated. There is 0.5% increase in mean annual rainfall during 1999–2008 as compared to 1989–1998. Month August is the 2^nd wettest month in all the districts except Purnia and Katihar during the 1^st period. On the other hand, the districts such as Nalanda, Munger, Sheikhpura, Jamui, Bhagalpur, Banka, Saharsa, Madhepura, Purnia, Katihar and Khagaria have been observed 2^nd wettest month in September during 2^nd period. Rainfall variability caused a change of -5.3% in rice area between triennium ending averages 1999–2000 and 2007–08. However, in case of wheat a meager increase of 1.6% was recorded. A slight change of -0.4% has been noticed during kharif maize, and 5.0 and 12.7%, in rabi and summer maize, respectively.As far as zonal change is concerned, all the zones, except zone IIIAhad a positive change in area of kharif maize and more over zone IIIB recorded a highest change of 57.7% due to decrease in monthly rainfall during August and September months. This feature compelled the farmers of the region to shift to kharif maize requiring less water