Impacts of Climate Change on Salmon, part II

Nate MantuaIngrid Tohver, and Alan Hamlet

JISAO CSES Climate Impacts GroupUniversity 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

patterns1. 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

HistoricalHistorical2080s A1B2080s A1B

Dramatic changes in snowmelt Dramatic changes in snowmelt systemssystems

• Snowmelt rivers become transient basins• Transient basins become rainfall dominant

• Models project more winter floodingmore 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 Summer base flows are projected to drop substantiallydrop substantially (5 to 50%) for most streams in western WA and the Cascades– The duration of the summer low flow season duration of the summer low flow season

is also projected to increase in snowmelt is also projected to increase in snowmelt and transient runoff riversand transient runoff rivers, and this reduces rearing habitat

Cool water, weak stratificationhigh nutrients, a productive “subarcticsubarctic” food-chain with abundant forage fish and few warm water predators

Warm stratified ocean, fewnutrients, low productivity “subtropicalsubtropical” 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 Upwelling food webs in our in our

coastal oceancoastal ocean

The future will not present itself in a The future will not present itself in a simple, predictable way, as natural simple, predictable way, as natural variations will still be important for variations will still be important for

climate change in any location climate change in any location

Overland and Wang Eos Transactions (2007)

Box1

oC

Deg

rees

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 What are the biological implications of ocean acidification?ocean acidification?

Barr

ie K

ovis

h

Pacific Salmon

Coccolithophores

Vic

ki F

ab

ry

Pteropods

Copepods

AR

CO

D@

ims.

uaf.

ed

u

(Slide provided by Dick Feely, NOAA)

Warmer lower

flows in summe

r

Floods

Acidification, warming,

winds?

Warm, lowstreamflow

Impacts summary for salmonImpacts 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