Effects of high local sea surface temperature on the extreme rainfall over the eastern coast of Australia in February 2022

Record-breaking extreme rainfall impacted Australia’s east coast from February to April 2022, causing severe flooding across the region. To explore the causative processes underlying this extreme rainfall, this study investigates the role of anomalously high sea surface temperatures (SSTs) along the east coast of Australia. The Weather Research and Forecasting model was used to conduct ensemble simulations with various SST and initial condition scenarios to examine the sensitivity of rainfall to oceanic conditions. During the event, SSTs in the East Australian Current (EAC) were nearly 2 °C above the 20-year climatological mean though this effect was offset by the unusually cold SSTs further offshore. This SST pattern influenced rainfall through two distinct mechanisms: a thermodynamic effect, where warmer SSTs enhanced surface evaporation and low-level moisture; and a dynamic effect, where SSTs above ~ 26 °C strengthened the southern flank of a coastal low-pressure system, enhancing onshore flow and shifting rainfall southward. The blocking high over southeastern Australia, combined with the low-pressure system off the coast, was the primary driver of extreme rainfall. We found that the intensity and spatial distribution of the SST anomaly influenced the location of this low-pressure system, enhancing the onshore flow and the rainfall produced. The results highlight the complex and threshold-dependent nature of SST impacts on extreme rainfall. Internal atmospheric variability also played a significant role, reinforcing the need for ensemble modelling to isolate SST-driven effects in real-world extreme events.