Probability Analysis of Annual Maximum Daily Rainfall for Karnataka, India

Abstract

Daily rainfall data for 22 years (2000–2022) were obtained from the Global Weather Data for SWAT and analyzed to assess annual and monthly rainfall variability. The annual series was examined to determine maximum and minimum rainfall values, while the monthly series was processed to evaluate monthly patterns. Statistical parameters such as standard deviation and coefficient of variation (CV) were also calculated for the study period. Results showed that the annual maximum daily rainfall varied widely between 1 mm and 10.55 mm, indicating substantial temporal variability. Monthly analysis revealed that October consistently received the lowest rainfall across all study years, whereas July and August recorded the highest rainfall, highlighting the dominance of the monsoon season. Among the months, August exhibited the lowest CV (58.35%), followed by September (61.82%), suggesting comparatively stable rainfall patterns during these months. In contrast, June recorded the highest CV (75.04%), indicating greater inter-annual variability. Further, frequency analysis showed that the maximum daily rainfall values estimated using both Normal and Log-Pearson Type III distributions at a 20% probability of exceedance were highest during the months of July to October.