Seasonal precipitation variability and its relationship with southern oscillation index in the recent four decades in Nepal

The time series data of 107 meteorological stations' precipitation from 1977 to 2018 were used to study seasonal precipitation variation in Nepal. In the past four decades, monsoon and winter precipitation have decreased. The mean precipitation during the monsoon season is 1433.42 mm and 69.67 mm in winter, respectively. The intrinsic heavy precipitation pattern was observed in the mountainous areas of central and eastern regions of Nepal. The western region has received heavier winter precipitation and decreases towards the eastern region. The correlation between the summer standardized anomaly and the Southern Oscillation Index (SOI) is moderate (0.52) for the monsoon. In contrast, the winter correlation is weaker (−0.32), suggesting an inverse relationship between SOI and winter precipitation. Generally, El Niño episodes are associated with precipitation deficits. In 1998 and 2016, episodes of both El Niño and La Niña led to heavy monsoon precipitation but it got reduced in winter. During the El Niño years, average winter precipitation is about 9.26%, above the long-term average. In La Niña years, winter precipitation is about 13.49% below the long-term average. Likewise, during the monsoon in El Niño years, average precipitation is about 9% below the long-term average (1977 to 2018). In La Niña years, average precipitation is approximately 9% above the long-term average.