By Jay Lund and Peter Moyle
In drought years, California usually reduces “environmental water flows” — the amount of river flows needed to maintain aquatic ecosystems — to make more water available for farms and cities. The current drought has been no exception. Depriving fish of adequate river flows, however, might not be in the interests of urban and agricultural users if it leads to long-term decline of species.
Reductions in environmental flows during the 1988-92 drought arguably sped the expansion of destructive clam and aquatic weed populations in the Sacramento-San Joaquin Delta. These invasive species have wreaked havoc on the Delta’s ecosystem and likely contributed to the decline of several open-water species, including delta smelt and longfin smelt (Winder and Jassby 2011; Sommer et al. 2007; Thomson et al. 2010; Moyle and Bennett 2008).
Reductions in cold-water releases from Shasta Dam helped lead to the 1990 listing of the winter-run Chinook salmon (Moyle et al. 2008). A recent study indicates that most California native fishes will suffer severe declines with climate change and eventually qualify for endangered species listings if deprived of adequate cold-water flows (Moyle et al 2013).
Diverting environmental flows to water users can lead to additional Endangered Species Act listings of native fish. This could require increased environmental flows to protect the listed species and jeopardize water diversions in the long run.
If the long-term value of the lost water supply is high enough, curtailment of environmental flows during a drought might not be worthwhile for most water users.
Consider the example in Figure 1, in which a simple risk-based decision analysis explores the long-term economic benefits to water users (not necessarily caring about fish).
Figure 1 – A Decision Tree on Environmental Flow Reduction during a Drought
The diagram shows a range of decision options – to reduce environmental flows or not – and a range of likely consequences for each decision – showing and structuring the effects of uncertainty and their consequences.
Table 1 gives rough numerical values for costs, benefits and consequences of each decision. And Table 2 shows results from the risk-based calculations. In this case, the values in Table 1 have been set to show the plausibility that a 500,000 acre-foot reduction in environmental flows might not provide a net long-term economic benefit to water users.
Progress in California water management and policy will require stakeholders to move beyond habitual conflicts and look toward their common long-term interests — for both water deliveries and the environment. Keeping native fish populations healthy may be the best long-term strategy for many water users.
Jay Lund and Peter Moyle are with the Center for Watershed Sciences at UC Davis. Lund is a professor of civil and environmental engineering and director of the center. Peter Moyle is a professor of fish biology.
Lund, J., E. Hanak, B. Thompson, B. Gray, J. Mount and K. Jessoe (2014), “Why give away fish flows for free during a drought?,” CaliforniaWaterBlog.com, Feb. 11, 2014
Raiffa, H. (1970), Decision Analysis: Introductory Lectures on Choices Under Uncertainty, Addison-Wesley Publishing Co.
Moyle, P. and W. Bennett (2008), The Future of the Delta Ecosystem and Its Fish, Appendix D to Comparing Futures for the Sacramento San Joaquin Delta, Public Policy Institute of California, San Francisco
Moyle, P.B., J.A. Israel, and S. E. Purdy. 2008. Salmon, steelhead, and trout in California: status of an emblematic fauna. UC Davis Center for Watershed Sciences. 316 pp.
Moyle, P.B., J. D. Kiernan, P. K. Crain, and R. M. Quiñones. 2013. Climate change vulnerability of native and alien freshwater fishes of California: a systematic assessment approach. PLoS One
Sommer, T., et al (2007), “The Collapse of Pelagic Fishes in the Upper San Francisco Estuary,” Fisheries, 32:6, 270-277
Thomson, J.R., W.J. Kimmerer, L.R. Brown, K.B. Newman, R. Mac Nally, W.A. Bennett, F. Feyrer and E. Fleishman (2010), “Bayesian change point analysis of abundance trends for pelagic fishes in the upper San Francisco Estuary”, Ecological Applications, 20(5), 2010, pp. 1431–1448
Winder, M. and A.D. Jassby (2011), “Shifts in Zooplankton Community Structure: Implications for Food Web Processes in the Upper San Francisco Estuary” Estuaries and Coasts (2011) 34:675–690