Abstract
The El Niño-Southern Oscillation (ENSO) drives substantial variability in precipitation and drought risk over Australia. Understanding the combined effect of anthropogenic forcing and ENSO on Australian precipitation extremes over the coming century can assist adaptation efforts. Here we use 24 CMIP5 climate models to examine externally forced changes in the frequency of “droughts”, when precipitation falls below the pre-industrial Decile 1 threshold. We focus on June to November (i.e., southern hemisphere Winter–Spring season) because precipitation during this period is important for agricultural production and recharging reservoirs in many parts of the country. The analysis in this paper is based on two 90-year simulations (1900–1989 and 2010–2099) for Historical and RCP8.5 scenarios. We show that the frequency of droughts, including droughts occurring in consecutive Winter–Spring seasons, is projected to increase in the twenty-first century under the RCP8.5 scenario in all eight Natural Resource Management (NRM) “clusters”. Approximately 60% of years are projected to be drought years in Perth, 35% in Adelaide, 30% in Melbourne, and approximately 20–25% of years in Sydney, Canberra and Brisbane. The relative frequency distributions of seasonally averaged Winter–Spring precipitation shift to lower values in all NRM clusters. However, apart from the Southern and Southwestern Flatlands, the shifts are accompanied by changes in the shape of the distributions whereby the high end of the distributions do not shift as much as other parts of the distribution and the wettest seasons become marginally wetter. This means that in most locations generally drier conditions are projected to be infrequently punctuated by seasons that are just as wet or wetter than the wettest years experienced during the twentieth century. While the models generally do a poor job in simulating ENSO precipitation teleconnections over Australia, an increase in ENSO-driven variability is suggested for the Wet Tropics, the Monsoonal North, the Central Slopes and the Southern and Southwestern Flatlands.
Highlights
Precipitation in Australia is projected to change in response to further global warming and in some regions, appears to have already been affected (CSIRO and Bureau of Meteorology 2015)
Values vary from a decrease of a few percent in the northwest, to increases of more 10% in most of southern Australia, with increases over 30% in the southwest and about 15–20% in Victoria
We found that a while a majority of the five models best able to simulate El Niño-Southern Oscillation (ENSO) teleconnections showed an increase in |El Niño and La Niña precipitation (E–L)| in all clusters, the majority was very marginal in all clusters except the Wet Tropics (4 out of 5 models showing an increase), the Monsoonal North (4 out of 5), the Central Slopes (4 out of 5) and Southern and Southwestern Flatlands (4 out of 5)
Summary
Precipitation in Australia is projected to change in response to further global warming and in some regions, appears to have already been affected (CSIRO and Bureau of Meteorology 2015). More recently Power and Delage (2018) pointed out that the precipitation during future El Niño-Southern Oscillation (ENSO) years is a function of both meanstate changes and changes in ENSO-driven variability They concluded, that while precipitation variability in CMIP5 models associated with ENSO is projected to increase in the tropical Pacific and corresponding increases are evident in many regions away from the Equatorial Pacific, the increases are modest, and are robust in only a handful of regions. They considered two large boxes involving Australia—one for “Northern Australia” and another for “Southern Australia/New Zealand” combined.
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