Relationship between the Indian Ocean Dipole (IOD) and Paddy Cultivation during Maha Seasons in Sri Lanka

Climate is one of the important factors that influence crop production. Paddy (Oryza sativa L.) is highly impacted by the variations in rainfall that occur within a growing season. This study was mainly focused on the major paddy-growing season in Sri Lanka, Maha season (October to February), under different phases of the Indian Ocean Dipole (IOD) phenomenon. Based on the IOD effective years, a comprehensive analysis was carried out using the paddy cultivation data recorded during the past 42 years (1979-2020). The observations were narrowed down to the major paddy-growing districts. A significant positive impact was found in all three paddy-growing ecosystems, namely, major irrigation and minor irrigation schemes and rainfed systems, during the IOD-positive years with an increasing rainfall. The rainfed cultivation showed the highest positive anomaly, followed by those under minor irrigation and major irrigation eco-systems during the IOD-positive period. The positive effect was more distinct in the gross harvested extent compared to the gross sown extent. The paddy production showed a statistically significant increase (P<0.05) and average yield also showed an apparent increase during IOD-positive years in almost all major paddy-growing districts. During IOD-negative years, negative anomalies of gross-sown and gross-harvested extents were observed in all three-paddy growing ecosystems. The paddy production and the average paddy yield also showed a reduction during IOD-negative years. The positive and negative impacts identified by this study during IOD-positive and negative years are useful for informed decision-making with a considerable lead-time during cultivation-planning for the Maha season.