Modeling cyclone risk variations in Australia by ENSO phases.

Historical cyclone data indicate significant variations in cyclone activity during different phases of the El Niño-Southern Oscillation (ENSO). However, the impact of these variations on cyclone risk and damage has not been thoroughly investigated due to limited historical loss record. Understanding these variations could be crucial for effective risk management.

This study examines the variation in cyclone risk associated with ENSO phases, utilizing the cyclone risk assessment model by Impact Forecasting for Australia. The model employs a stochastic event set of cyclones, representing about forty-two thousand years of basin-wide activity, developed using environmental data from reanalysis and machine learning techniques. Our analysis demonstrate that the stochastic event set accurately reflects the seasonal variation in cyclone activity due to ENSO phases, making it a reliable tool for risk assessment.

To evaluate risk by ENSO phases, we segregated the stochastic event set using the Oceanic Nino Index and estimated wind-driven losses for each phase. The model results shows a significant variation in cyclone risk in Australia during El Niño and La Niña. However, the risk during the Neutral phase is found to be comparable with the long-term average. Annual average losses (AAL) during La Niña increases by 40%, while El Niño phases show a 37% reduction compared to the long-term average. Additionally, a one-in-hundred-year event during La Niña can result in 21% higher losses, whereas losses are 28% lower during El Niño compared to the long-term average.

The modeled loss variations across ENSO phases are consistent with observed changes in cyclone activity in Australia and are supported by the historical loss records.