Impacts of Climate Change on Salmon, part II Nate Mantua Ingrid Tohver, and Alan Hamlet JISAO CSES Climate Impacts Group University of Washington Harley Soltes/Seattle Times

What we did Hydrologic models were forced by downscaled precipitation and surface temperature data for “historic”, 2020s, 2040s, and 2080s (Elsner et al.) –Using the “VIC model” at 1/16˚ resolution; with multimodel composite A1B and B1 scenarios, respectively We analyzed simulated streamflow records at 97 locations for monthly average patterns, daily peak flows, and 10 day average summer low flows (base flows)

Why we chose these factors Peak flows: large flood events reduce egg-to-fry and parr survival rates Summer low flows = rearing habitat for fish with stream type life histories Seasonal runoff patterns are closely related to life history types and the biodiversity of salmon

3 basic streamflow patterns 1. rain-dominated 2. “transient” basins with an early winter peak from rainfall, and a spring peak from snowmelt 3. snowmelt-dominated basins, where streamflow peaks in late spring and early summer Historical 2080s A1B

Dramatic changes in snowmelt systems Snowmelt rivers become transient basins Transient basins become rainfall dominant

more winter floodingModels project more winter flooding in sensitive “transient runoff” river basins that are common in the Cascades –Likely reducing survival rates for incubating eggs and rearing parr

Summer base flows are projected to drop substantiallySummer base flows are projected to drop substantially (5 to 50%) for most streams in western WA and the Cascades duration of the summer low flow season is also projected to increase in snowmelt and transient runoff rivers –The duration of the summer low flow season is also projected to increase in snowmelt and transient runoff rivers, and this reduces rearing habitat

Cool water, weak stratification subarctic high nutrients, a productive “subarctic” food-chain with abundant forage fish and few warm water predators Warm stratified ocean, few subtropical nutrients, low productivity “subtropical” food web, a lack of forage fish and abundant predators Recently, warm ocean years have generally been poor for NW chinook, coho and sockeye, but good for Puget Sound pink and chum salmon. Upwelling food webs in our coastal ocean

The future will not present itself in a simple, predictable way, as natural variations will still be important for climate change in any location Overland and Wang Eos Transactions (2007) Box1 oCoC Degrees C

Reduced calcification rates for calcifying (hard-shelled) organisms and physiological stress Shifts in phytoplankton diversity and changes in food webs Reduced tolerance to other environmental fluctuations Potential for changes to fitness and survival, but this is poorly understood What are the biological implications of ocean acidification? Barrie Kovish Pacific Salmon Coccolithophores Vicki Fabry Pteropods Copepods (Slide provided by Dick Feely, NOAA)

Warmer lower flows in summer Flood s Acidification, warming, winds? Warm, low streamflow Impacts summary for salmon

Impacts will vary depending on life history and watershed types Low flows+warmer water = increased pre-spawn mortality for summer run salmon and steelhead –Clear indications for increased stress on Columbia Basin sockeye, summer steelhead, summer Chinook, also Lake Washington sockeye and Chinook Increased winter flooding in Puget Sound streams – an increased stressor on egg-to-fry survival rates for fall spawners, and overwinter survival rates for yearling parr (steelhead, coho, and stream-type chinook)

Impacts of Climate Change on Salmon Recovery in the Snohomish River (Battin et al. 2007: PNAS) Climate Change will make salmon restoration more difficult: Decreasing Summer/Fall Low Flows Increasing Winter Peak Flows Increasing water temperatures in critical periods Decreasing Spawning Flows Increasing Winter Flows

Mitigating projected impacts Reduce existing threats caused by land/water use that impair natural hydrologic processes – Protect and restore instream flows in summer – Identify and protect thermal refugia – Reconnect, restore and protect off-channel habitat in floodplains Glines Canyon Dam, Elwha River

Increased conflict over use of surface water in summer Human demands on surface water are projected to increase during times of high salmon vulnerability

Planning for a warmer future The potential for increased conflict over scarce summer water begs for strategic policy thinking that recognizes trade-offs will have to be made –Developing clear decision-guidance now may be an effective way to avoid future crises and potentially high-cost conflicts