Rainfall in Australia's eastern seaboard: a review of confidence in projections based on observations and physical processes

Dowdy, Andrew J.; Grose, Michael; Timbal, Bertrand; Moise, Aurel; Ekström, Marie; Bhend, Jonas; Wilson, Louise

doi:10.22499/2.6501.008

Cited by 27 publications

(21 citation statements)

References 63 publications

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“…The resultant confidence estimates range from Medium to High, depending on season and region, and is generally higher than for other regions of Australia (such as the eastern seaboard: Dowdy et al (2015)) due to the relatively high degree of evidence and agreement for the southern Australia rainfall projections.…”

Section: Discussionmentioning

confidence: 89%

Seasonal and regional signature of the projected southern Australian rainfall reduction

Hope¹,

Grose²,

Timbal³

et al. 2015

AMOJ

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A projected drying of the extra-tropics under enhanced levels of atmospheric greenhouse gases has large implications for natural systems and water security across southern Australia. The drying is driven by well studied changes to the atmospheric circulation and is consistent across climate models, providing a strong basis from which adaptation planners can make decisions. However, the magnitude and seasonal expression of the drying is expected to vary across the region. Here we describe the spatial signature of the projected change from the new CMIP5 climate models and downscaling of those models, and review various lines of evidence about the seasonal expression.Winter rainfall is projected to decline across much of southern Australia with the exception of Tasmania, which is projected to experience little change or a rainfall increase in association with projected increases in the strength of the westerlies. Projected winter decrease is greatest in southwest Western Australia. A 'seasonal paradox' between observations and CMIP5 model projections in the shoulder seasons is evident, with strong and consistent drying projected for spring and less drying projected for autumn, the reverse of the observed trends over the last 50 years. The models have some biases in the simulation of certain synoptic types (e.g. cutoff lows), the rainfall brought by those synoptic types, and the mechanism of rainfall production. Rainfall projections based on statistical downscaling are examined in relation to some of these biases, projecting stronger future declines in some regions of southeast Australia in autumn than indicated by the host models, as well as little change to the magnitude of the projected declines in spring. Apart from Tasmania in winter, the decline of rainfall in southern Australia during the cool season remains a confident projection but the seasonal expression of change remains an ongoing research topic.

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Section: Discussionmentioning

confidence: 89%

Seasonal and regional signature of the projected southern Australian rainfall reduction

Hope¹,

Grose²,

Timbal³

et al. 2015

AMOJ

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“…The results presented here suggest that further investigation of changes to the rainfall distribution and synoptic climatology in GCMs compared to downscaling is worthwhile, particularly for spring but also for summer and autumn. Also see review of physical plausibility of changes in Dowdy et al (2015).…”

Section: Discussionmentioning

confidence: 99%

“…Projected changes to rainfall associated with these synoptic systems are either currently unavailable or have a high degree of uncertainty associated with them in the east Australia region (see Dowdy et al, 2015). However, the intensity of the severe weather events (including heavy rainfall) associated with these systems is likely to b e better represented by certain downscaling methods than by the relatively coarse spatial and temporal scales of current GCMs (e.g.…”

Section: Introductionmentioning

confidence: 99%

Comparison of various climate change projections of eastern Australian rainfall

Grose¹,

Bhend²,

Argüeso³

et al. 2015

AMOJ

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The Australian eastern seaboard is a distinct climate entity from the interior of the continent, with different climatic influences on each side of the Great Dividing Range. Therefore, it is plausible that downscaling of global climate models could reveal meaningful regional detail, or 'added value', in the climate change signal of mean rainfall change in eastern Australia under future scenarios. However, because downscaling is typically done using a limited set of global climate models and downscaling methods, the results from a downscaling study may not represent the range of uncertainty in plausible projected change for a region suggested by the ensemble of host global climate models. A complete and unbiased representation of the plausible changes in the climate is essential in producing climate projections useful for future planning. As part of this aim it is important to quantify any differences in the change signal between global climate models and downscaling, and understand the cause of these differences in terms of plausible added regional detail in the climate change signal, the impact of sub-sampling global climate models and the effect of the downscaling models themselves. Here we examine rainfall projections in eastern Australia under a high emissions scenario by late in the century from ensembles of global climate models, two dynamical downscaling models and one statistical downscaling model. We find no cases where all three downscaling methods show the same clear regional spatial detail in the change signal that is distinct from the host models. However, some downscaled projections suggest that the eastern seaboard could see little change in spring rainfall, in contrast to the substantial rainfall decrease inland. The change signal in the downscaled outputs is broadly similar at the large scale in the various model outputs, with a few notable exceptions. For example, the model median from dynamical downscaling projects a rainfall increase over the entirety of eastern Australia in autumn that is greater than the global models. Also, there are some instances where a downscaling method produces changes outside the range of host models over eastern Australia as a whole, thus expanding the projected range of uncertainty. Results are particularly uncertain for summer, where no two downscaling studies clearly agree. There are also some confounding factors from the model configuration used in downscaling, where the particular zones used for statistical models and the model components used in dynamical models have an influence on results and produce additional uncertainty.

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“…Further evidence for an anthropogenic role in the observed increase in the frequency of major flooding is provided by the latest IPCC report (2014) Dowdy et al (2015) concluded that there is high confidence in a projected increase in the frequency of extreme rainfall throughout the eastern seaboard of Australia. These and other consistent conclusions (Reisinger et al 2014) relate to future changes.…”

Section: Discussionmentioning

confidence: 99%

The frequency of major flooding in coastal southeast Australia has significantly increased since the late 19th century

Power¹,

Callaghan²

2016

JSHESS

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Millions of Australians live in a 1500 km stretch of coastal catchments in southeast Australia. Major flooding in this region causes death, economic loss and major disruptions to the lives of its inhabitants. Concerns have been raised that anthropogenic climate change might lead, or has already led, to an increased risk of extreme rainfall and associated flooding. Images of flooding commonly appear in the media, fuelling perceptions that flood frequency has already increased. Here we use a new dataset that allows us to estimate reliable trends over much longer periods than has previously been the case. The statistical significance of the trends is assessed using a method that is suitable for the nonGaussian, serially correlated flood frequency data. We identify a statistically significant, increasing trend in the frequency of major floods since the late 19th century, which contributes to a 50% increase in frequency. While possible reasons for the increase are discussed (e.g. land use change, anthropogenic climate change, natural climate variability), further research is needed to clarify the relative importance of possible contributors.

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Rainfall in Australia's eastern seaboard: a review of confidence in projections based on observations and physical processes

Cited by 27 publications

References 63 publications

Seasonal and regional signature of the projected southern Australian rainfall reduction

Seasonal and regional signature of the projected southern Australian rainfall reduction

Comparison of various climate change projections of eastern Australian rainfall

The frequency of major flooding in coastal southeast Australia has significantly increased since the late 19th century

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