Analyzing Extreme Precipitation during the Prolonged Summer Monsoon of 2022 in Nepal: Insights from Hourly Observational Data

The South Asian Summer Monsoon is a vital part of the broader Asian monsoon system, heavily influencing atmospheric circulation, regional climate, and water resources across South Asia. Nepal, located on the southern slopes of the Himalayas, receives approximately 80% of its annual rainfall during the summer monsoon (June-September), which significantly impacts agriculture, water availability, and disaster risks. This study focuses on analyzing the diurnal variation, spatial distribution, and intensity of extreme precipitation events in Nepal during the 2022 monsoon season. Using hourly precipitation data from 63 meteorological stations across Nepal, the study investigates rainfall patterns from June to September 2022. The monsoon season of 2022 began earlier than usual on June 5th, extending for 134 days, the longest on record in Nepal. Despite its extended duration, the total rainfall was not significantly higher than average, with western Nepal experiencing below-normal precipitation and eastern regions receiving slightly above-normal rainfall. The analysis of spatial variation revealed considerable disparities in rainfall distribution, with the Lumle area recording the highest precipitation (3133 mm) and several western districts observing minimal rainfall. Diurnal analysis highlighted a consistent pattern of nighttime precipitation dominance, with the highest rainfall occurring around 9 PM and the lowest around 6 AM. Approximately 60% of the total monsoon rainfall occurred during nighttime hours. This diurnal cycle was consistent across Nepal’s major regions, suggesting large-scale atmospheric influences like monsoon troughs and southwesterly winds. The study also assessed extreme precipitation events, defined as rainfall exceeding 40 mm/h. These events were widespread across Nepal, with central and eastern regions experiencing a higher frequency of extreme rainfall compared to western areas. The findings emphasize significant spatial variability in precipitation intensity and duration, critical for understanding regional monsoon dynamics and improving disaster preparedness.