Assessment of Long- Term Rainfall Variability and Seasonality in the Mysuru Region Using 58 Years of Observational Data

Aims: The present study aimed to analyze long-term rainfall variability and seasonal distribution in the semi-arid region of southern Karnataka, with a focus on understanding its implications for agricultural planning and climate-resilient farming strategies in the Mysuru region. Study Design: A retrospective time-series analytical study based on long-term observed rainfall data. Place and Duration of Study: The study was conducted using rainfall data recorded at the Weather Observatory of the Agro-Meteorological Field Unit (AMFU), Organic Farming Research Station (OFRS), Naganahalli, Mysuru, under the Gramin Krishi Mausam Sewa programme, covering a period of 58 years from 1968 to 2025. Methodology: Monthly and annual rainfall data were subjected to descriptive statistical analysis to evaluate temporal variability, inter-annual fluctuations, seasonal contributions, and extreme rainfall years. Seasonal rainfall distribution was assessed for southwest monsoon, northeast monsoon, summer, and winter periods. Long-term rainfall trends were analyzed using the non-parametric Mann–Kendall test and Sen’s slope estimator. Results: The mean annual rainfall of the study area was 693.2 mm, with a high coefficient of variation (>30%), indicating substantial inter-annual variability. Annual rainfall ranged from severe deficit years (1300 mm). The southwest monsoon season (June–September) contributed the largest share of annual rainfall, followed by the northeast monsoon season (October–November), confirming a bimodal rainfall pattern. October recorded the highest mean monthly rainfall, underscoring its importance for kharif crop maturity and rabi crop sowing. Trend analysis revealed a weak, non-significant increasing tendency in annual rainfall, suggesting that variability rather than long-term change dominates rainfall behavior in the region. Conclusion: The pronounced rainfall variability and frequent extremes pose significant challenges to rainfed agriculture in the Mysuru region. The long-term rainfall characterization provides a robust baseline for climate-resilient agricultural planning, water resource management, and future agro-climatic research.