Atmospheric River Clustering in the Western United States with Seasonal Cycles and Climate Modes

Atmospheric rivers (ARs) bring much of the winter precipitation to the western United States and are important for water supply and flood hazards. This study analyzes the clustering of ARs and evaluates how seasonal cycles and climate modes influence their frequency and spacing. Daily precipitation records and reanalysis data from 1980–2021 were used to detect ARs with an integrated vapor transport threshold, and events were grouped when two or more ARs occurred within a 7-day window. The results show that models capture the general occurrence of ARs but underestimate clustering by about 20–30%, with larger errors in winters affected by El Niño and La Niña. Sensitivity tests show that cluster measures depend on threshold and time window choices, while regional differences are linked to topography and circulation. The results suggest that persistence and spacing should be studied as separate measures, and that higher-resolution models are needed to represent narrow moisture plumes and rapid sequences. Although limited by dataset length and resolution, this study provides guidance for improving seasonal forecasts and for supporting water and flood management in AR-prone regions.