compared across environmental workgroups. This is a consequence of the substantial and increasing interactions between workgroups that the Committee witnessed over the course of two years, the overlap between scientists working on multiple workgroups, and the oversight of the Lead Scientist Ed Lowe, who provided continual input to the workgroups as they developed their rankings.
Several tables summarizing the results of the WSIS [found in Lowe et al. (2011)] are presented below. Table 4-1 shows the effects, ranging from negligible to extreme, for each of the major hydrologic drivers, by river segment. This table can be considered to represent the worst possible realistic scenario, as it includes a large withdrawal and 1995 land use, but completion of the upper basin projects and no sea level rise. Changes in flow rate precipitated by scenario FwOR1995PN are predicted to have moderate effects in segments 1-3 on fish and (consequently) wildlife. Also in the estuarine portion of the river, changes in salinity are expected to have moderate effects on wetlands vegetation and minor effects in benthic macroinvertebrates. Water age effects brought about by withdrawal are expected to have minor impacts on the plankton communities in segments 2-4. Changes in water level in river segments 5-8 are expected to moderately affect wetlands, fish, and wildlife. Finally, entrainment or impingement could have major effects on fish in upper basins locations where the withdrawal is likely to occur, but these could be ameliorated by proper intake design, as noted in Chapter 3. Considering all drivers, salinity in the lower river and water level changes in the upper river are likely to have the largest effects on river ecology, particularly on fish. Potential entrainment/impingement issues further highlight fish as a vulnerable ecological community.
More specific information can be gleaned from Table 4-2, which shows the levels of effects for each environmental workgroup by segment, under the scenario that was most extreme for that workgroup. The Full1995PN scenario was found to cause the most extreme effects for five workgroups (wetlands, biogeochemistry, benthos in the upper river, fish, and wildlife), and the effects range from negligible (for biogeochemistry) to moderate (for benthos, fish, and wildlife). The most extreme scenarios for the plankton and SAV workgroups produced only negligible effects. Summing these effects over all workgroups leads to the same results apparent in the final column of Table 4-1: moderate effects are likely in the lower river due to salinity and flow rate issues, and in the upper river due to changes in water levels. The District’s approach of using the lowest denominator in terms of a level of effect—across all metrics within a workgroup, across hydrologic drivers in Table 4-1, and across workgroups in Table 4-2—represents an application of the precautionary principle that is appropriate.
On the other hand, the workgroups did not appear to consider the possibility of “back-to-back extreme events in their analyses, e.g., two or three years of extreme drought in a row, which the Committee considers to be reasonably likely future situations. They also tended to present mean responses to perturbations of a given driver with little or no consideration of the variance in that response. Although mean values are considered the most likely responses from a statistical perspective, in analyzing potential environmental impacts of changes in driver variables it is important to consider ranges (or variances) of responses. Although such responses may be less likely than mean values, they may not have negligible probabilities and they also could be much more detrimental than the mean responses. The Committee remains concerned that the District did not consider such conditions sufficiently in their otherwise thorough analyses.