Projected increase in ENSO-induced US winter extreme hydroclimate events in SPEAR large ensemble simulation

Abstract

Observational records during the past several decades show a marked increase in boreal winter extreme US hydroclimate events, with extreme floods and droughts becoming more common. Coincidentally, El Niño-Southern Oscillation (ENSO), a key driver of US precipitation and associated extreme hydroclimate on interannual time scales, has also increased in amplitude and is projected to continue increasing throughout the 21st century. This study examines future changes in ENSO and its impacts on the US winter extreme hydroclimate events (e.g., drought and flood) by using a large ensemble simulation. Results in this study show that both the amplitude of ENSO and ENSO-induced atmospheric teleconnections are projected to strengthen, leading to a significant increase in US precipitation variability and extreme hydroclimate events, albeit with notable regional differences. Signal-to-noise ratio analysis shows that the ENSO signal explains a significantly increased fraction of the total variance in US winter precipitation compared to non-ENSO factors (i.e., noise), suggesting a growing role of ENSO in future US extreme hydroclimate events. Further analysis shows that while both the increase in ENSO amplitude and the atmospheric response to ENSO have a similar impact on the hydroclimate over the Southeast and Southwest US, the amplification of the atmospheric response to ENSO plays a more dominant role in the Northeast US.