Climate Change Impacts on Flood Frequency, Intensity, and Timing May Affect Trout Species in Sagehen Creek, California

Abstract

AbstractClimate warming is likely to alter the frequency, intensity, and seasonal timing of floods in Sagehen Creek, a headwater stream in California's Sierra Nevada, and thus has the potential to alter the population dynamics of brook trout Salvelinus fontinalis and rainbow trout Oncorhynchus mykiss. Both species are susceptible to floods that can scour redds or kill fry, potentially decreasing population size the following summer. Winter (November—April) floods affect brook trout, and spring (May) floods affect rainbow trout. In this study, we applied a spatially distributed ecohydrologic model (RHESSys) to estimate how climate warming (+2°C and +4°C) and changes in precipitation are likely to impact flood flows in Sagehen Creek. Model estimates predict substantial changes in the temporal distribution of floods from spring to winter and an increase in the frequency and intensity of floods in both warming scenarios. Greater annual precipitation or precipitation intensity increases flood frequency but does not change the temporal distribution. Results show a seasonal shift from mostly spring floods under current conditions (54 spring and 12 winter flood‐days) to almost entirely winter floods in the +4°C warming scenario (5 spring and 83 winter flood‐days), which would disproportionately impact brook trout populations. Given that this change in the timing of floods would probably be combined with greater flood intensity and higher stream temperatures, we argue that warming will likely cause a long‐term decline in brook trout abundance. Conversely, fewer spring floods and potentially decreased competition with brook trout are likely to have a positive impact on the abundance of rainbow trout in Sagehen Creek, although increases in precipitation intensity would negatively impact both species. A shift in the abundance of either species may impact recreational anglers and have resource management implications.