Trends of rainfall and its likely impact on crop production in four agro-ecological zones of Bihar

The rainfall data of Pusa, Purnia, Sabour and Gaya representing different Agro-ecological zones (Zone I, II, III A, III B, respectively) of Bihar were analyzed on monthly, seasonal and annual time scales using long period data (1971–2010). Mann-Kendall non-parametric test was employed for trend analysis of monthly, seasonal and annual precipitation for different period viz. 1971–1980 (DP1), 1981–1990 (DP2), 1991–2000 (DP3), 2001–2010 (DP4) and for long period 1971–2010 (LP). Zone III A showed significant decreasing trend of 42.85 mm/year annual rainfall in recent decadal period (DP4). Zone III B showed significant decreasing trend of annual rainfall during long period (LP) but there was increasing trend of 4.57 mm/year during recent decadal period (DP4) and 0.43 mm/year during long period (LP) in pre-monsoon/summer season. August and September months showed significant decreasing trend of 2.12 mm/year and 2.62 mm/year rainfall, respectively, in long period (LP) in zone III B, which may affect the transplanting/vegetative phase of the rice crop. Decreasing trend of rainfall in post monsoon season in all the zones during recent decadal period (DP4) as well as during long period (LP) is delaying/affecting the sowing of wheat crop.