An Assessment of Climatic Risk and Temporal Trend of Rainfed Crop Potential in the Sub-Himalayan Plains of West Bengal

Abstract

This study assessed water availability, climatic risk and temporal trends for Kharif transplanted rice and rainfed Rabi crops in six blocks of Alipurduar district of Sub-Himalayan West Bengal, viz, Alipurduar I & II combined, Falakata, Madarihat, Kalchini and Kumargram, using IMD gridded rainfall (1921–2020) and temperature (1951–2020) data. Trends in water availability parameters were analyzed using the non-parametric Mann–Kendall test and Sen’s slope estimator, while crop water balance components and length of growing period (LGP) were estimated following the Thornthwaite and Mather (1955) approach. Kharif rainfall exhibited a significant declining trend (47-87 mm/Decade) at three of the five locations. Only 20–24% (20–26 Standard Meteorological Week [SMW]) and 29–33% (28–30 SMW) of seasonal rainfall was stable and effective for transplanted rice, with lower values at Madarihat. Assured LGP exceeded 200 days in three out of four years, indicating low risk for rainfed double cropping, although LGP variability was relatively higher at Kumargram and Madarihat. For rainfed yellow sarson sown at 42 SMW, stored soil moisture met about 50% of crop water requirement, declining by 20–22 mm per fortnight with delayed sowing up to 48 SMW. Overall, water availability conditions for rainfed crops, in terms of LGP, showed improvement (1.7-2.4 days /Decade) across the study locations.