Pick Our Brain - January 2009

What are some of the expected effects of climate change on fish in the Delta?

There are numerous types of effects to consider. One is the direct effect of rising temperatures. Water temperatures are known to correlate closely with air temperatures. Therefore, warming of the climate by 2 degrees C will have a similar effect on water temperatures. This is of concern when water temperatures reach levels that are stressful or lethal to fish. There are studies that point to stressful or lethal temperatures being reached for salmon and delta smelt with this level of warming. These effects could be exacerbated by heat waves and low flows.

Other effects are much more difficult to evaluate. For example, climate change is very likely to deliver more water to California as rain versus snow and peak runoff from our rivers will occur earlier in the spring or winter. The effects of a change in the timing of high flows on Delta fish are less clearly understood. Major life cycle process like fish migration and reproduction are keyed to flow. It is unclear whether fish of the Delta can adapt or if they will be severely by these changes. Another example of an indirect effect is the strong likelihood that extreme weather conditions will accompany climate change. Extreme droughts and floods are predicted to become more common. The effects of these extreme events on the fish of the Delta are not well known, but are likely to place further stress on fish species. The direct effects of climate change are very likely to be important, but the additional effects that we can and cannot forecast may well be even more significant.