potential-impacts-of-climate-change-on-the-swan-and-canning-rivers

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Figure 9 Time series <strong>of</strong> Fremantle sea level anomaly with the linear trend removed The red line shows the interannual variability in the record obtained by running a 19 year Hanning window to remove the long-term tidal effects Source: Elliot and Pattiaratchi (in preparation) 1.5.5 Seasonal total rainfall A steep decrease in autumn/winter rainfall occurred in the early 1970s throughout the region, accompanied by a slight increase in spring and summer. These <strong>change</strong>s have been described in detail in reports and bulletins <strong>of</strong> IOCI and are illustrated in Figure 10. The <strong>change</strong>s are associated with <strong>change</strong>s in cyclogensis (see section 1.4.3). Figure 10 Change in daily flows for 1952 – 75 compared with 1976 – 99 for Yarragil Brook near Dwellingup Source: IOCI (2005b) 25
120 100 80 60 mm 40 20 0 Jan Feb Mar A pr May Jun Jul Aug Sep Oct Nov Dec Average monthly rainfall for the south west <strong>of</strong> line from Jurien to Bremer Bay. M onth 1925-1975 1976-2003 Figure 11 Average monthly rainfall for south west <strong>of</strong> a line from Jurien to Bremer Bay Source: IOCI (2005a) Regional average rainfall for winter months decreased by 10 per cent during this period while rainfall from May - July decreased by 15 per cent (Figure 11). Although records for the last decade indicate further drying, a longer timeframe is necessary to assess whether the observed <strong>change</strong>s are statistically signifi cant. 1.5.6 Annual and daily river flows Regional streamfl ow has markedly decreased as a result <strong>of</strong> diminished winter rainfall. In extreme cases this has equated to more than 50 per cent reduction <strong>of</strong> run<strong>of</strong>f into metropolitan catchments. In general, the greatest <strong>change</strong> is observed in the catchments draining higher rainfall areas. Overall, these variations in fl ow have been observed from month to month as well as at an annual scale. An example <strong>of</strong> <strong>change</strong> in daily stream fl ow between 1952 and 1999 is illustrated in Figure 10. A comparison <strong>of</strong> fl ow duration curves for 1952 – 1975 and 1976 – 1999 indicates that the river is dry more frequently in recent years. 1.5.7 Extreme rainfall and flooding While <strong>change</strong>s in seasonal records have been apparent, a signifi cant shift in extreme rainfall is more diffi cult to ascertain. Although existing records give an insight into extreme events occurring at a relatively frequent scale (e.g. 1 to 10 years), the recurrence intervals <strong>of</strong> rare, disaster level events are signifi cantly harder to determine. Extreme winter rainfall events as a cause <strong>of</strong> winter flooding A consistent decrease in annual and winter rainfall has been observed throughout the south west <strong>of</strong> Western Australia since the mid 1970s. In addition, rainfall records indicated that the occurrence <strong>of</strong> large storms in winter months had signifi cantly decreased as had winter extremes in daily rainfalls. This was reinforced by research conducted by Li et al. (2005) who determined that winter extreme daily rainfalls with up to 50 year return periods have decreased since 1965. As with the aforementioned decrease in annual rainfall, it is likely that multi-decadal variability is contributing to these observed <strong>change</strong>s in extreme winter rainfall events. In addition to the effects <strong>of</strong> discrete rainfalls, winter fl ooding is heavily infl uenced by antecedent conditions (how wet the catchment is before the storm event). For example, the major winter fl ood 26
Page 1 and 2: Potential impacts
Page 3 and 4: 2.2 Impacts on Swan and Canning rRi
Page 5 and 6: List of Figures Fi
Page 7 and 8: Preamble During the 21 st century t
Page 9 and 10: Increased development of</s
Page 11 and 12: from a diverse range of</st
Page 13 and 14: Figure 1 Mean surface temperature -
Page 15 and 16: 1.1.4 Weather patterns and rainfall
Page 17 and 18: Table 3 Atmospheric CO 2 concentrat
Page 19 and 20: Figure 3 Multi-model averages and a
Page 21 and 22: Table 6 Projected globally averaged
Page 23 and 24: on the region (remote forcing). For
Page 25: waters leading to low levels <stron
Page 29 and 30: Table 9 Major water quality trends
Page 31 and 32: Table 10 Observed and projected (so
Page 33 and 34: Table 11 Projected annual mean warm
Page 35 and 36: 1.6.4 Storm surges Storm surge occu
Page 37 and 38: mate (see IOCI 2005d). This leaves
Page 39 and 40: Table 15 Observed and projected (so
Page 41 and 42: 2 POTENTIAL CLIMATE CHANGE IMPACTS
Page 43 and 44: phorus) in river runof</str
Page 45 and 46: (after microbial decomposition) to
Page 47 and 48: Trophic dynamics Trophic dynamics a
Page 49 and 50: and squid now more consistently abu
Page 51 and 52: pools); and • result in a reducti
Page 53 and 54: the Swan River. Observations <stron
Page 55 and 56: Figure 15 - Waves overtopping a sea
Page 57 and 58: Human and social economics The prim
Page 59 and 60: 3 Adaptation to the impacts
Page 61 and 62: Table 19 Climate change</st
Page 63 and 64: Further, assessment of</str
Page 65 and 66: Area / issue Likelihood Adverse imp
Page 67 and 68: Area / issue Likelihood Adverse imp
Page 69 and 70: extension of mudfl
Page 71 and 72: • apply planning legislation to l
Page 73 and 74: Table 23 Economic impacts</
Page 75 and 76: State and local government planning
Page 77 and 78:
Amelioration / adaptation Provide d
Page 79 and 80:
increase system resilience. Economi
Page 81 and 82:
Acknowledgements Technical Advisory
Page 83 and 84:
Intergovernmental Panel on Climate
Page 85 and 86:
Appendix 1: Draft Scenarios for Swa
Page 87 and 88:
dangerous instabilities in global <
Page 89 and 90:
Table A4 Projected mean winter rain
Page 91 and 92:
Table A9 Qualitative summary <stron
Page 93 and 94:
Appendix 2: Rainfall/streamflow sce
Page 95 and 96:
Parameter Temperature increase deg
Page 97 and 98:
Table 2-3 Projected winter rainfall
Page 99 and 100:
GHG reduced it to 95 %, other anthr
Page 101 and 102:
Appendix 3: Emission Scenarios <str
Page 103 and 104:
improvement rates in all supply and
Page 105 and 106:
Per 30 yrs (2000-2030) = 0.057 to 0
Page 107 and 108:
Black Swan and some ducks but will
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