Climatic Background to Past and Future Floods in Australia

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Publisher Summary

This chapter discusses climatic background and future floods in Australia. Floods in the Murray–Darling Basin (MDB) can be due to local severe storms leading to flash flooding, or to heavy rains from much larger scale systems leading to basis-wide great floods that can take months to travel downstream. The Basin is subject to large scale rain events from diverse synoptic origins, mainly tropical lows in the summer half year in the northern region and fronts and cutoff lows in the southern sector during the winter half year. Great year-to-year variability is associated with fluctuations in the El Nińo–Southern Oscillation (ENSO) regime, and there have been marked interdecadal variations in rainfall in the past, some of which have occurred abruptly. Changes due to the enhanced greenhouse effect will include higher temperatures and increased potential evaporation, and likely increases in rainfall intensity associated with major storm systems, including cutoff lows of both tropical and midlatitude origin. Annual mean rainfall is generally expected to increase in northern regions of the MDB, especially inland, but to decrease in the southernmost areas south of the Murray River. Changes in rainfall intensity in models are scale-dependent, with finer resolution models generally predicting larger increases. More work is needed to resolve these uncertainties, and to apply flood routing to rainfall scenarios.

Section snippets

Summary

Rainfall variability in Australia is generally among the highest in the world, largely due to the dominant influence of the El Niño–Southern Oscillation. Australian climate has been characterized by wet and dry periods with sometimes sudden transitions from one mode to the other. Synoptic explanations and teleconnections are discussed, with an emphasis on the Murray–Darling Basin (MDB). Floods in Australia are generally of two types: local “flash floods” and widespread basin flooding. The

Geographic and Climatic Setting

Humans tend to see floods as water that is out of place, inundating normally dry land used or potentially used by humans. However, floods can also be seen as part of the natural process that deposits silt and nourishment on flood plains and periodically maintains vegetation and wildlife, especially water birds. Floods as a hazard are largely conditioned by the degree of human adaptation to floods. In Australia's early years of European colonization, flood hazards loomed large because of lack of

Interannual Variability of Rainfall

The large variability of Australian rainfall is due to variations in large‐scale influences including the El Niño–Southern Oscillation (ENSO), the latitude of the westerlies and variations in standing wave patterns associated with blocking phenomena (Fig. 2).

The pattern of rainfall variability associated with ENSO is a dominant influence on the frequency and intensity of floods in the MDB, with the center of its influence situated right over the Basin, where it accounts for up to a third of the

The Paleoclimatic Record

At the time of the last glacial maximum, some 20,000 years ago, the MDB region was in general wetter, but most of this was due to the much colder conditions, and rainfall was probably less, with fewer intense rain events (Hesse et al., 2004). There is evidence that the Willandra Lakes and others in the region were full and fresh, with Aboriginal occupation and remains nearby (Bowler 1998, Smith 2005).

However, by the time of the postglacial maximum warming around 8000–6000 years ago, the

The Instrumental Record

Instrumental records of Australian rainfall began in the mid‐nineteenth century. As records became longer, fluctuations in the rainfall record were analyzed (Deacon 1953, Kraus 1954, Gentilli 1971). They all noted a wetter period in the MDB in the late nineteenth century then a drier period in the first half of the twentieth century. Pittock (1975) analyzed twentieth century rainfall records, examining the influence of the high‐pressure belt (and by implication, the latitude of the midlatitude

Recent Trends and Observations

Observational data indicate that the climate of Australia and the MDB has changed considerably since 1950. Both Smith (2004) and Collins and Jones (personal communication, 2005) have used data from the Bureau of Meteorology high‐quality station network to analyze trends in rainfall and temperature for Australia.

Strong contrasts in rainfall trends (Fig. 3A) are evident throughout the country and seasons since 1950. The eastern part of the country, including the MDB, has experienced strong

Climate Change Projections

Regional climate change scenarios, that is, projections of possible or plausible climate changes as a result of the enhanced greenhouse effect, were first mooted in the late 1970s, and the first for the Australian region in the early 1980s (Pittock and Salinger, 1982). These were based on primitive general circulation models of the climate, with grossly simplified oceans, crude analogies with past warm epochs and ensembles of individual warm versus cool years, and elementary theoretical

Conclusions

Floods in the MDB can be due to local severe storms leading to flash flooding, or to heavy rains from much larger‐scale systems leading to basin‐wide great floods which can take months to travel down stream. The Basin is subject to large‐scale rain events from diverse synoptic origins, mainly tropical lows in the summer half year in the northern region and fronts and cutoff lows in the southern sector during the winter half year. Great year‐to‐year variability is associated with fluctuations in

Acknowledgments

Thanks are due to fellow members of the Climate Impacts, Adaptation and Risk group in CSIRO Marine and Atmospheric Research, and in particular to Tony Rafter for help with graphics and Ian Smith for valuable comments. Thanks are also due to Dean Collins and David Jones of the Australian Bureau of Meteorology in Melbourne for data and Figures, Martin Thoms of the University of Canberra for help with Table 1, and Mike Smith of the National Museum of Australia for additional comments.

References (83)

  • W. Cai et al.

    Evidence for a time‐varying pattern of greenhouse warming in the Pacific Ocean

    Geophys. Res. Lett.

    (2000)
  • W. Cai et al.

    Fluctuations in the relationship between ENSO and northeast Australian rainfall

    Clim. Dyn.

    (2001)
  • W. Cai et al.

    The response of the Antarctic Oscillation to increasing and stabilized atmospheric CO2

    J. Clim.

    (2003)
  • D.A. Collins et al.
  • W. Craik
  • E.L. Deacon

    Climatic changes in Australia since 1880

    Aust. J. Phys.

    (1953)
  • L.B. Devin et al.
  • K. Emanuel

    Increasing destructiveness of tropical cyclones over the past 30 years

    Nature

    (2005)
  • K. Emanuel

    Emanuel replies

    Nature

    (2005)
  • A.M. Fowler et al.

    Potential impacts of global warming on the frequency and magnitude of heavy precipitation

    Nat. Hazards

    (1995)
  • S.W. Franks

    Identification of a change in climate state using regional flood data

    Hydrol. Earth Syst. Sci.

    (2002)
  • S.W. Franks et al.

    Flood frequency analysis: Evidence and implications of secular climate variability, New South Wales

    Water Resour. Res.

    (2002)
  • J. Gentilli

    Climatic fluctuation: Climates of Australia and New Zealand

    World Surv. Climatol.

    (1971)
  • L.C. Grimmer

    The rain event of 25–26 January 1984 over the Australian Capital Territory and surrounding districts of New South Wales

    Meteorological Note 180

    (1988)
  • K.J. Hennessy et al.

    Changes in daily precipitation under enhanced greenhouse conditions

    Clim. Dyn.

    (1997)
  • K.J. Hennessy et al.

    Australian rainfall changes, 1910–1995

    Aust. Meteorol. Mag.

    (1999)
  • K.J. Hennessy et al.
  • G.J. Holland et al.

    Australian east‐coast cyclones, I, Synoptic overview and case study

    Mon. Weather Rev.

    (1987)
  • C.D. Hoyas et al.

    Deconvolution of the factors contributing to the increase in global hurricane intensity

    Science

    (2006)
  • M. Hulme et al.

    Relative impacts of human‐induced climate change and natural climate variability

    Nature

    (1999)
  • R. Jones et al.
  • R.N. Jones et al.

    Climate change and water resources in an arid continent: Managing uncertainty and risk in Australia

  • R.T. Kingsford

    Ecological impacts of dams, water diversions and river management on floodplain wetlands in Australia

    Aust. Ecol.

    (2000)
  • H. Kirkup et al.

    Temporal variability of climate in south‐eastern Australia: A reassessment of flood‐ and drought‐dominated regimes

    Aust. Geogr.

    (1998)
  • T.R. Knutsen et al.

    Impact of CO2‐induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization

    J. Clim.

    (2004)
  • E.B. Kraus

    Secular changes of tropical rainfall regime of southeast Australia

    Q. J. R. Meteorol. Soc.

    (1954)
  • E.B. Kraus

    Secular changes of east‐coast rainfall regimes

    Q. J. R. Meteorol. Soc.

    (1955)
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