Climate Drivers Compound Under Climate Change

Abstract

Seasonal climate variability in south-east Australia is influenced by three major climate drivers; the El Niño-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). Each climate driver has impacts upon seasonal rainfall, temperature and fire risk. In south-east Australia, there is some evidence that large scale fire seasons are more likely to occur when there are compounding impacts from more than one driver. Seasonal impacts on rainfall and temperature can also be stronger when more than one driver is active. In this thesis, publicly available output from global climate models is used to explore how anthropogenic climate change may alter the frequencies these climate drivers compound in the future. Results from 35 global climate models submitted to the Coupled Model Intercomparison Project phase 6, and from the Community Earth System Model Last Millennium Ensemble were analysed. Models include experiments to represent pre-industrial climate, historical climate, and a high greenhouse gas emission scenario for the future climate. Indices to represent the state of ENSO, IOD and SAM were calculated and then seasons where more than one mode is compounding to promote more extreme wet or dry conditions in south-east Australia were found. In the future scenario, the frequency of dry-promoting compounds increases consistently in the models examined, in both the cool season and warm season. The frequency of wet-promoting compounds also increases in the warm season for some models. ENSO and IOD variability promotes dry conditions more frequently, while SAM moves to a more positive mean state, which promotes dry conditions in the cool season and wet conditions in the warm season. Although compound events become more frequent, there is no clear change in the strength of the rainfall and temperature impacts from compound events in the future scenario. The changes to event frequencies occur in the context of a long-term increase in air temperature, and seasonal changes to average rainfall. A reduction in cool season rainfall, and increased air temperatures, mean that dry-promoting compound events would have a greater impact when they occur. Increased air temperatures and increased frequency of dry-promoting compounds mean that fire frequency would be expected to increase in the future. Global action to reduce greenhouse gas emissions would reduce or delay the increase in dry-promoting compound events and fire risk. Increasing frequency of dry-promoting climate variability in south east Australia, should be considered in ongoing research and adaptation to climate change. Show more