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

Abstract

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 (<300 mm) to extreme excess 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.