Association of Western US Compound Hydrometeorological Extremes with MJO and ENSO Interaction

Extreme weather and climate events have substantial impacts on global socioeconomic conditions and the environment. Recent studies have suggested that compound extremes (two or more extreme events occurring simultaneously or successively) may exert even larger impacts than individual events. In this study, we discuss the physical drivers behind variability in hydrometeorological (precipitation and temperature) compound extremes over the western United States (US) on subseasonal-to-seasonal timescales.

The Madden-Julian oscillation (MJO) is a convection-circulation coupled system in the tropics varying primarily on subseasonal timescales. It strongly modulates extratropical weather and climate and is recognized as a key source of subseasonal and seasonal predictability. Here, we present observational evidence through composite analysis which indicates that compound extreme frequency over the western US region is strongly linked to the MJO. The linkage between MJO and compound extremes is largely dependent on the El Niño-Southern Oscillation (ENSO) phase and amplitude, which can be seen through different magnitudes or changes in sign of the canonical relationship conditioned on ENSO states. Similarly, the MJO can interrupt the canonical ENSO-compound extreme relationship. Our results suggest a potential route to improve subseasonal and seasonal prediction of western US compound extremes by considering the combined effect of both MJO and ENSO.