by Peter Moyle 

Close relatives of mine live in Asheville, North  Carolina.  Retired professors, they chose to move there in part because of its pleasant climate. This quiet community was hit hard by Hurricane Helene, on September 27, 2024. The path the hurricane took through Asheville was unprecedented and heavy rains and flooding resulted in widespread treefalls, with damage and destruction to homes, buildings, roads, and other infrastructure. They watched the quiet little creek below their community become a raging torrent that moved boulders and trees. They lost electricity and internet for a couple of weeks and had potable tap water restored only after about 2 months.  There is little doubt that the severity and unexpected  pathway of the hurricane were the result of climate change, starting with the warming of the Atlantic Ocean. More rogue hurricanes can be expected. Such major events are increasingly likely as the planet warms (Palmer 2024). 

I live in Davis, California and sometimes wonder if we Davisites are too complacent in recognizing that a similar or even bigger flood event might happen to us.  At some point, we may experience a megaflood in the Central Valley (Moyle et al. 2023). Indeed, the whole landscape of the Central Valley is shaped by major flood events. The incredibly rich and flat farmland on which we live and build is the result of aperiodic massive floods that carried fine sediment originating in the Coast Range to the Valley floor where it was deposited as the flood water lost its energy.  Sediment cores show such floods have occurred once every 150 to 200 years (Ingram and Malamud-Roam 2013). The last such flood, a small one by geologic standards, was in 1861-1862 when the Central Valley became an “Inland Sea” (Kelley 1989). Sacramento was underwater and the newly elected governor famously had to be rowed from his house to the building where he was sworn in, on the second floor. 

In Davis, we are protected, in theory, from large floods by Monticello Dam on Putah Creek. The dam created a large reservoir for retaining flood water. In addition, below the dam, levees on both sides of the lower creek concentrate the creek’s flows so they down-cut the channel on the valley floor for much of the lower creek’s length. The high flows have caused the creek to excavate a canyon of sorts which carried potential flood waters to the Putah Creek Sinks, now part of the Yolo Bypass. The bypass is a huge farmed area that is maintained to protect the city of Sacramento from flooding (Opperman et al. 2017).  The bypass is scheduled to be enlarged, to increase its capacity for flood flows. Changes in infrastructure and management are also underway to make the bypass more fish-friendly by allowing for improved upstream passage of returning adult salmon as well as for rearing habitat, on flooded areas, for juvenile salmon, splittail, and other fishes. 

California has done, and continues to do, an amazing job of increasing floodable areas to help protect people, as well as the native biota, especially fish and waterfowl. We are fortunate also that the native fishes, as the result of millions of years of evolution, are adapted to take advantage of high flows and widespread flooding in the Central Valley (Moyle 2002). However, many non-native species, such as common carp and largemouth bass, are also adapted to live with floods, so there could be a biological race to see what fish species prevail in the years following major floods (Moyle 2017). Floods of the magnitude of the 1861-62 flood -or bigger- will occur within the next 50-100 years, thanks to global warming. Directly or indirectly, each flood will affect Davis and the UCD campus in unexpected ways and we need to act accordingly. For example, the ongoing rebuilding of the UCD Arboretum Waterway is shaping up. It is being labeled as a flood management project to help protect the campus, as well as a refuge for native plants and animals. We need more projects like that, only on a much larger scale.   

“This year, 52% of properties in Yolo County have risk of flooding. In 30 years, 54% of properties in Yolo County will have risk of flooding. https://firststreet.org/county/yolo-county-ca/6113_fsid/flood.” These estimates are likely conservative.  Maybe we Davisites should be worried about flooding.

Peter B. Moyle is a Distinguished Professor Emeritus at the University of California, Davis and is Associate Director of the Center for Watershed Sciences. 

Further Reading

Ingram, L. and F. Malamud-Roam 2013. The West without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us About Tomorrow. Berkeley: University of California Press.

Kelley, R.   1989  Battling the Inland Sea. Berkeley: University of California Press.

Moyle, P.B. 2002. Inland Fishes of California. Revised and expanded. Berkeley: University of California Press.

Moyle, P.B., J. Lund, and N. Pinter. 2023. Living with Extreme Floods in California. California WaterBlog. Center for Watershed Sciences, July 14, 2023.  https://californiawaterblog.com/2023/07/30/living-with-extreme-floods-in-california/

Moyle, P.B. 2013. Warmer water will kill off most of California’s native fishes. California WaterBlog. Center for Watershed Sciences, May 31, 2013. https://californiawaterblog.com/2013/05/31/warmer-water-will-kill-off-most-of-californias-native-fishes/

Moyle, P.B. 2017. What do stream fish do during flood flows?  UCD Center for Watershed Sciences California Water Blog, March 5 2017.

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.

Opperman, J.J, P.B. Moyle, E.W. Larsen, J.L. Florsheim, and A.D. Manfree. 2017. Floodplains: Processes, Ecosystems, and Services in Temperate Regions. Berkeley: University of California Press.

Palmer, T. 2024. Seek Higher Ground: the Natural Solution to Our Urgent Flooding Crisis. Berkeley, University of California Press.