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Authors: Pui, A., Lall, A., Sharma, A.Acknowledgments: Australian Research Council
Positive Phase 1Negative PhasePositive Phase 2The IPO is a coherent pattern of sea surface temperature (SST)variability ov...
Kiem, Anthony S. et al., "Multi-decadal variability of flood risk." Geophysical Research Letters, 2003: 1-4.Negative Phase...
1. Do antecedent wetness conditions influencethe design flood estimate?2. Does design rainfall vary between opposingIPO ph...
PiCatchment Antecedent Conditions are approximated byANTECEDENT PRECIPITATION INDEX (API):Where :• P = annual maximum 24 h...
 High P is defined as above 50thpercentile annual rainfall maxima
><High rainfall corresponding to high flows is mostlikely when catchment in a wetter state
Test Statistic:H0 : No. Stations Iratio > 1 <= No. Stations Iratio < 1HA : No. Stations Iratio > 1 > No. Stations Iratio < 1
Proportion:Australia wideIratio > 1 = 0.64East AustraliaIratio > 1 = 0.61Not significant as perfield significance test(0.9...
Test Statistic:H0 : No. Stations APIratio > 1 <= No. Stations APIratio < 1HA : No. Stations APIratio > 1 > No. Stations AP...
APIratio > 1APIratio < 1Proportion:Australia wideAPIratio > 1 = 0.78East AustraliaAPIratio > 1 = 0.86Significant as per fi...
We have shown:1. antecedent wetness conditions influence thedesign flood estimate2. Variation in design rainfall between o...
YearsYearsRainfallAEP(%)DurationIntensityStreamFlowStreamFlowRainfallYearsStreamFlowAnnual Maximum P IFD Relationship Floo...
StreamFlowFlood Frequency CurveAEP(%)Rainfall HyetographRainfallRainfallStreamFlowStreamFlowAEP(%)AEP(%)
• Future approaches for flood estimation needto account for the non-stationary character ofantecedent moisture.• This seri...
Alexander PuiSchool of Civil & Environmental Engineering, UNSWEmail: a.pui@student.unsw.edu.au
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IPO Antecedent Precipitation Presentation

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Some thoughts on how the IPO affects flood risk in East Australia...

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IPO Antecedent Precipitation Presentation

  1. 1. Authors: Pui, A., Lall, A., Sharma, A.Acknowledgments: Australian Research Council
  2. 2. Positive Phase 1Negative PhasePositive Phase 2The IPO is a coherent pattern of sea surface temperature (SST)variability over the Pacific Ocean occurring on inter-decadaltimescalesPower, S.B., T. Casey, C Folland, A Colman, and V Mehta, 1999: Inter-decadal modulation of the impact of ENSOon Australia. Climate Dynamics, 15, 319-324Recent studies have shown that Flood Risk is not stationaryand is conditioned to the IPO phase
  3. 3. Kiem, Anthony S. et al., "Multi-decadal variability of flood risk." Geophysical Research Letters, 2003: 1-4.Negative Phase :Increased Flood RiskPositive Phase :Decreased Flood Risk1 in 6 year flood (IPO –ve)1 in 100 yearflood (IPO+ve)Flood risk is influenced by the IPO.Is this caused by changes in design rainfallor antecedent conditions?
  4. 4. 1. Do antecedent wetness conditions influencethe design flood estimate?2. Does design rainfall vary between opposingIPO phases?3. Do antecedent conditions vary betweenopposing IPO phases?
  5. 5. PiCatchment Antecedent Conditions are approximated byANTECEDENT PRECIPITATION INDEX (API):Where :• P = annual maximum 24 hour rainfall amount• i = day on which the annual maximum event occurs• K = API exponential decay factor ( 0.92)• n is the specified time lag (10)K Pi-1K2Pi-2K3Pi-3KnPi-nCordery I . Antecedent wetness for design flood estimation. Civil Eng Trans I E Aust 1970; 12:181–5
  6. 6.  High P is defined as above 50thpercentile annual rainfall maxima
  7. 7. ><High rainfall corresponding to high flows is mostlikely when catchment in a wetter state
  8. 8. Test Statistic:H0 : No. Stations Iratio > 1 <= No. Stations Iratio < 1HA : No. Stations Iratio > 1 > No. Stations Iratio < 1
  9. 9. Proportion:Australia wideIratio > 1 = 0.64East AustraliaIratio > 1 = 0.61Not significant as perfield significance test(0.95%)Iratio > 1Iratio < 1
  10. 10. Test Statistic:H0 : No. Stations APIratio > 1 <= No. Stations APIratio < 1HA : No. Stations APIratio > 1 > No. Stations APIratio < 1
  11. 11. APIratio > 1APIratio < 1Proportion:Australia wideAPIratio > 1 = 0.78East AustraliaAPIratio > 1 = 0.86Significant as per fieldsignificance test(0.95%)
  12. 12. We have shown:1. antecedent wetness conditions influence thedesign flood estimate2. Variation in design rainfall between opposingIPO phases is not statistically significant3. However, antecedent conditions varysignificantly between opposing IPO phases?What does this mean for currentapproaches to Design Flood Estimation?
  13. 13. YearsYearsRainfallAEP(%)DurationIntensityStreamFlowStreamFlowRainfallYearsStreamFlowAnnual Maximum P IFD Relationship Flood Frequency CurveContinuous P Annual Maximum Q Flood Frequency CurveAEP(%)
  14. 14. StreamFlowFlood Frequency CurveAEP(%)Rainfall HyetographRainfallRainfallStreamFlowStreamFlowAEP(%)AEP(%)
  15. 15. • Future approaches for flood estimation needto account for the non-stationary character ofantecedent moisture.• This seriously compromises the assumptionthat design rainfall leads to design floods (‘AEPneutrality’).• Also beware of rainfall-runoff modelscalibrated to data from a single IPO state.
  16. 16. Alexander PuiSchool of Civil & Environmental Engineering, UNSWEmail: a.pui@student.unsw.edu.au

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