Assessment of Rainfall Variability and Seasonal Shifts in Saharsa District, Bihar, India

Abstract

Rainfall variability strongly influences agricultural planning and water-resource management in monsoon-dependent regions. This study assessed annual variability and seasonal shifts in rainfall in Saharsa district, Bihar, using weekly records organized by Standard Meteorological Week for 2020–2025. Annual totals ranged from 993.1 mm in 2024 to 1496.3 mm in 2020, with a mean of 1212.83 mm. The coefficient of variation was 18.14%, indicating moderate inter-annual variability. Linear regression produced a slope of −106.68 mm year⁻¹. Rainfall anomalies were positive in 2020 and 2021 and negative from 2022 to 2025. Seasonal analysis showed that the monsoon season (SMW 22–39) supplied the largest proportion of    annual rainfall, but rainfall was unevenly distributed, with high weekly totals interspersed with prolonged dry spells. Pre-monsoon and post-monsoon rainfall varied between years, whereas winter rainfall was negligible. The number of rainy days ranged from 45 to 72, with an annual average of 58.5 days. The observed temporal concentration of rainfall may increase the risk of waterlogging, runoff loss, and crop moisture stress. The findings support the need for rainwater harvesting, supplementary irrigation,   drainage improvement, adjusted sowing schedules, and strengthened agrometeorological advisories in Saharsa district.