Stream flow and temperature maps - Effect of Climate Change on Salmon Population Vulnerability

1. Steelhead (Oncorhynchus mykiss) and other Pacific salmon are threatened by unsustainable
   levels of harvest, genetic introgression from hatchery stocks and degradation or loss of freshwater
   habitat. Projected climate change is expected to further stress salmon through increases
   in stream temperatures and altered stream flows.
2. We demonstrate a spatially explicit method for assessing salmon vulnerability to projected
   climatic changes (scenario for the years 20302059), applied here to steelhead salmon across
   the entire Pacific Northwest (PNW). We considered steelhead exposure to increased temperatures
   and more extreme high and low flows during four of their primary freshwater life stages:
   adult migration, spawning, incubation and rearing. Steelhead sensitivity to climate change
   was estimated on the basis of their regulatory status and the condition of their habitat. We
   assessed combinations of exposure and sensitivity to suggest actions that may be most effective
   for reducing steelhead vulnerability to climate change.
3. Our relative ranking of locations suggested that steelhead exposure to increases in temperature
   will be most widespread in the southern Pacific Northwest, whereas exposure to substantial
   flow changes will be most widespread in the interior and northern Pacific Northwest.
   There were few locations where we projected that steelhead had both relatively low exposure
   and sensitivity to climate change.
4. Synthesis and applications. There are few areas where habitat protection alone is likely to
   be sufficient to conserve steelhead under the scenario of climate change considered here.
   Instead, our results suggest the need for coordinated, landscape-scale actions that both
   increase salmon resilience and ameliorate climate change impacts, such as restoring connectivity
   of floodplains and high-elevation habitats.

Stream flow and temperature gridded data for PNW.