Climate Change Predictions and Management Options from Coupled Watershed and Population Dynamics Models: The Example of Spring-Run Chinook Salmon in California

Spring-run Chinook salmon (Oncorhynchus tshawytscha) are vulnerable to climate change because adults over-summer in freshwater streams before spawning in autumn. We sought to determine which future streamflow and water temperature regimes could lead to long-term reductions in spring-run Chinook salmon in a California stream and evaluate management adaptations to ameliorate these impacts. We used bias-corrected and spatially downscaled climate data from six General Circulation Models and two emission scenarios for the period 2010 – 2099, as input to two linked models: WEAP to simulate weekly mean streamflow and water temperature in Butte Creek, California that was used as input to SALMOD, a spatially explicit and size/stage structured model of salmon population dynamics in freshwater systems. Under these climate scenarios WEAP yielded lower summer base flows and higher water temperatures relative to historical conditions, while SALMOD yielded increased adult summer thermal mortality and population declines for all climate scenarios and model combinations. Of management adaptations tested, only ceasing water diversion for power production from the summer holding reach resulted in cooler water temperatures, more adults surviving to spawn, and extended population survival time, albeit with a significant loss of power production. Without changes in water management, spring run Chinook salmon are likely to go extinct in Butte Creek and elsewhere in California.