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Figure 5.3: Approach used to generate and apply future scenarios for the North Shore City Council study on future wet weather overflows

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Source: North Shore City Council et al 2003.

Text description of figure

This chart assists the North Shore City Council staff to assess expected system performance of wet weather overflows based on changing extreme rainfall events.


Analysis of process

Result or outcome


Intensity-Frequency-Duration analysis of historical rainfall and expected changes in rainfall due to global warming and IPO phase change (IFD tables of historical and expected future rainfall: 2050)

Establish relationship between historical and future rainfall IFD tables


Analyse historical rainfall data Determine storm characteristics (Rainfall-Intensity- Duration and preceding condition)

Estimate storm characteristics under future climate condition (Using existing storm characteristics and IFD relationships) Also incorporates results from Step 1 above


Analyse and relate system performance (overflows, storm water runoffs etc from long-term simulation) with storm characteristics (Rainfall-Intensity-Duration of overflow or runoff; Statistical Model)

Estimate characteristics of system performance under future condition (Intensity-Duration of overflow or runoff for each storm and long-term system performance IFD) Also incorporates results from Step 2 above


Compare system performance under historical condition (adopted in planning process) and expected future condition (IPO phase change and global warming) Incorporates results and outcomes from step 3

Note: Steps 3 and 4 are repeated for each system performance indicator (system overflow)