What iffing. What if X increased by 20%?

The following scenarios were evaluated...

1. Benchmark flow conditions, virgin mouth operation.
2. Benchmark flow conditions, mouth kept open.
3. Present day flow.
4. 20% increase in irrigation.
5. 20% increase in dams.
6. 20% increase in forestry.
7. 20% increase in irrigation, dams and forestry.

Input data sequences for the various scenarios were estimated using the Pitman model. To evaluate the risks associated with these scenarios, the input sequences where bootstrapped to 4000 years and the models run.

Figure's 36, 37, 38, 39 and 40 display the results.

  
Figure 36: The risks on salinity in Catalina associated with various scenarios for development.

  
Figure 37: The risks on salinity in False Bay associated with various scenarios for development.

Notes on the salinity boxplots....

• The benchmark flow, virgin mouth condition has a very high maximum salinity. This is because of the possibility of an extended drought resulting in a closed mouth and near ``lake empty'' conditions.
• Increasing development has very little effect on the salinity of the lake. The lake has a very high natural rainfall and a vast surface area. Thus the effect of the changes in the flow regime of the rivers is heavily moderated by the rainfall.
• Whilst it is true to say that very little effect would be had by further development, it must be realized that development has already had a significant impact on the lake. Thus one can argue that we should in fact be attempting to ameliorate the existing effects rather than increasing development.

  
Figure 38: The risks on the richness index associated with various scenarios for development.

  
Figure 39: The risks on the responsive richness index associated with various scenarios for development.

  
Figure 40: The risks on the biomass index associated with various scenarios for development.

One curiosity is that the ecosystem indices are better under present day conditions than under benchmark flow with virgin mouth operation. This is because the present day system is far more marine in nature, and the indices are heavily weighted towards species richness and biomass. Thus the lake is now more suitable for the many marine species.