Atmospheric teleconnection patterns and hydrological whiplashes in the Western U.S.

The Western U.S. is undergoing notable transformations in its hydrological patterns, distinguished by rising variability and recurrent "whiplash" shifts between extreme wet and dry phases. Our comprehensive analysis of 469 streamflow stations from 1981 to 2023 reveals a substantial increase in hydrological whiplash events, with a peak of 206 stations experiencing dry-to-wet whiplash in the early 1990s. We establish strong links between these streamflow extremes and sub-seasonal to seasonal teleconnection factors, particularly the Western Pacific Oscillation (WP) and Eastern Pacific/North Pacific Oscillation (EPO). Additionally, we demonstrate the combined impacts of the El Niño-Southern Oscillation (ENSO) and the Madden-Julian Oscillation (MJO), with MJO Phases 2/3 showing a positive relationship (correlation coefficients = 0.45) with wet conditions in the Pacific Southwest from October to December. Future projections using CMIP5 and CMIP6 models indicate increasing precipitation variability across the region. Notably, the CMIP5 RCP 8.5 scenario projects more volatile conditions than other scenarios. The results emphasize the pressing need for water management strategies that are both adaptive and flexible, to cope with the growing unpredictability of the hydrological cycle in the Western U.S.