Aquatic Species Responses to Changes in Streamflow and Stream Temperature in the Willamette River Basin of Oregon

Abstract:

Climate models project less summer precipitation and hotter temperatures in the Pacific Northwest. These changes will bring earlier snowmelt and reduced summer flow, which will increase stream temperature. Many cold water species will be adversely affected by such changes. However, the spatial and temporal extent of how each stream responds to climate change and how fish species respond to varying degrees of changes in flow and stream temperature across multiple streams has not been thoroughly studied. Using a combination of representative downscaled climate data, a watershed hydrologic model, and regression analysis, we projected future changes in streamflow and temperature and the responses of fish habitat to these changes for several tributaries of the Willamette River basin that exhibits distinct hydrologic landscape regions. Our simulation results suggest that streams located in the High Cascades where groundwater input is high will experience less warming and less flow reduction, thus more resilient to warming. In contrast, streams in transient areas where snow cover is projected to decline substantially will experience the most declines in fish diversity as a result of reduction in flow and highest rise in stream temperature. Our results suggest spatially targeted adaptive management strategies for fishes in a large heterogeneous river basin will be necessary in a rapidly changing climate.