Long period trend analysis of annual and seasonal rainfall in West Bengal, India (1901- 2020)

Abstract

Abstract The present study assessed long period (1901–2020) trends and magnitudes of seasonal and annual rainfall across districts of West Bengal. The non-parametric Mann-Kendall test and Sen’s slope estimator applied on the gridded (0.5˚ × 0.5˚) rainfall dataset. We used von Neumann ratio test (p < 0.05) for data homogenization. Tested autocorrelation using lag-1 autocorrelation coefficient (r1) at p < 0.05 and removed serial correlations if any using trend-free pre whitening (TFPW) technique. Results revealed that, both the annual and seasonal rainfall of West Bengal increased (at 0.02 mm year− 1 to 0.04 mm year− 1) non significantly (p > 0.05), except winter rainfall which decreased at 0.01 mm year− 1. Annual rainfall across the districts of sub Himalayan West Bengal (SHWB) declined. On the contrary, significant (p < 0.05) increase of annual rainfall observed across most of the districts of Gangetic West Bengal (GWB) at the rate of 1.8 mm year− 1 to 2.9 mm year− 1. Monsoon rainfall increased significantly (p < 0.05) over Gangetic West Bengal (GWB) at 1.4 mm year− 1 to 2.1 mm year− 1, while declined significantly (p < 0.05) in Dakshin Dinajpur district at 3.2 mm year− 1 of SHWB. Post-monsoon rainfall increased significantly (p < 0.05) over GWB at the rate of 0.2 mm year− 1 to 0.6 mm year− 1. The winter rainfall decreased non-significantly across all the districts except Dakshin Dinajpur, where significant (p < 0.05) decrease (@ 0.10 mm year− 1) observed. Thus, the derived location specific information on seasonal rainfall trends have immense utility in devising crop planning as well as livelihood security in West Bengal.