Impact of Climate Variability on Atmospheric River Clustering in the Western United States

Atmospheric rivers (ARs) are narrow corridors of concentrated moisture transport that deliver much of the extreme precipitation in the western United States, but their clustering behavior is not well represented in many climate studies. This study examined how seasonal variability and major climate modes such as El Niño and La Niña affect the frequency and clustering of AR events. Multi-decadal reanalysis datasets and observational records were used to quantify clustering through consecutive AR days and event sequences. The results show that clustering is about 28% higher during El Niño phases compared with neutral years, while La Niña phases produce fewer but more spatially concentrated events. These outcomes indicate that AR persistence is strongly shaped by large-scale climate drivers rather than occurring randomly, with direct consequences for flood forecasting and water resource planning. The study concludes that including climate variability in AR prediction systems can improve the accuracy of seasonal forecasts, although further work is needed to resolve local precipitation processes and address gaps in observations.