climate change in the green- the green/duwamish river ...€¦ · 26.10.2016 · duwamish estuary...

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Department of Natural Resources and ParksWater and Land Resources Division

The Green/Duwamish RiverWatershed

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LowerGreen RiverSubwatershed

MiddleGreen River

Subwatershed

UpperGreen RiverSubwatershed

Duwamish EstuarySubwatershed

Climate Change in the Green-Duwamish Watershed

Impacts on the Physical, Natural, and Human

Environment

Guillaume Mauger Climate Impacts Group WRIA 9, 26 Oct 2016

ClosingtheClimateGap

Science Prac*ce

“whatweknow”

“whatwe’redoingaboutit”

cig.uw.edu

Scoping Climate Science and Decision-Support Needs for Floodplain Management in Puget Sound

Guillaume Mauger, Climate Impacts Group, UW

Overview

The purpose of this document is to begin defining an agenda for the science and engagement efforts needed to support the consideration of climate change in multi-objective floodplain management. To do this, we propose a 3-tiered approach involving work at the regional, watershed, and project scales (Table 2). At each level, efforts to advance the science will be accompanied by stakeholder engagement aimed at defining science priorities and advancing the capacity to incorporate climate impacts in decision-making.

In the sections below we have summarized a number of actions, with their associated outcomes, assuming that the geographic scope is limited to the Puget Sound catchment. In writing the descriptions below, specific watersheds and projects have intentionally been omitted from the descriptions. Over the course of this project, it became clear that the discussions needed to identify the specific science and data needs of each stakeholder or project would require much more than was scoped for the current effort. Instead, we have distilled the results of these conversations into a set of research gaps that would address a wide range of planning and project needs, as well as a number of actions that would serve to further elucidate the science needed to support multi-objective floodplain management in the region.

Both feasibility and cost for this work will depend on the exact combination of efforts, priorities, and funding that is available for leverage. Moreover, these efforts can be undertaken by any number of entities in the region, depending on suitability and expertise. Nearly all of the efforts would require some degree of collaboration; potential partners include the many agencies, non-profits, and other institutions in the region.

Finally, it is important to emphasize that the tasks outlined in this document are intended to be a starting point for discussion. A comprehensive assessment of research gaps would require a larger evaluation involving researchers and stakeholders with varying points of view and expertise.

Table 1. Climate Architecture for Developing a Research Approach and Climate Work Plan for TNC.

Risk and Opportunity Assessment/Education

Policy and Planning

Implementation

Working with stakeholders to identify key interests and concerns, and developing science and data products that are tailored to decision needs.

Institutionalizing climate in regional funding, permitting, and policy decisions

Where to place projects to address specific climate risk, and how high to build your new levee.

Project/Reach Scale

The Lower XX river reach is at increased risk due to sea level rise, increased sedimentation and increased flood frequency and magnitude (all could be quantified). Tributary flows, engineered protections, agriculture and habitat considerations, or other specific issues are incorporated when focusing in on the project scale.

Updates to CFHMP, Salmon plans, and other plans include watershed-specific climate information, providing a basis for evaluating project ideas and prioritizing them relative to one another.

Lower XX and XX Creek suite of projects identified and designed to be resilient to climate change.

Watershed

Peak and low flows, reservoir operations, stream temperature, sediment transport, and hydrodynamic modeling necessary to make reach scale conclusions.

Projects are implemented in the headwaters to retain sediment and flood waters while parallel acquisition efforts retain opportunity in the floodplains.

Regional

Every major floodplain in Puget Sound will experience increases in 100-year flood events ranging from an increase of 18-55%, on average, however floodplain vulnerabilities extend beyond flooding, including sediment, water temperatures, sea level rise. Regional resources are targeted and sequenced as informed by climate risk/opportunity.

Ecology and PSP budgets and research plans; Legislative support; State and federal guidance documents.

Funding is driven towards research (analysis, modeling and data collection), monitoring, and implementation of projects that are deemed necessary in the face of climate change.

Playingthelongandtheshortgame

Awareness

Assessment

Analysis

Planning

Photo credit: Marli Miller

Climate Impacts

What does the science tell us?

2000 2050 2100

CO2−

SRES A1FIRCP 8.5SRES A2RCP 6.0SRES A1bRCP 4.5SRES B1RCP 2.6OBS

Greenhouse gas “scenarios” are best guesses about future emissions

Substantial Warming, Variable Rainfall

Historical

Low Emissions (RCP 4.5)

High Emissions (RCP 8.5)

1950 1975 2000 2025 2050 2075 2100

Temperature Difference(Relative to 1950−1999 average)

Precipitation Change(Relative to 1950−1999 average)

1950 1975 2000 2025 2050 2075 2100

−40%

−20%

−40%

−20%

ClimateChange:PhysicalDrivers

SeaLevelRise

Warming,Rainfall

Forests,Freshwater

Surge/Waves,OceanpH

OceanAcidifica*on

•  By2100,oceanpHisprojectedtodecreaseby–0.14to–0.32([H+]increaseof+38to+109%)

•  VariabilityinupwellingcanstronglyaffectpH

SeaLevelRise

PhotobyHughShipman,WADept.ofEcology

•  Pastcentury:about+8in.

•  By2100:+24in.(range:+4to+56in.)

•  Localratesofrisevary.

•  Noincreaseinstormsurge,buthigherseaswillcarrysurgefartherinland.

AlkiBeach,WestSea`le,January21,2010PhotobyHughShipman,WADept.ofEcology

Warner,Mass,Salathé,JHydromet,2014

More Intense Heavy Rains

Heaviestraineventsareprojectedtobecome+22%moreintense(range:+5to+34%)bythe2080s.

Ourprimarymechanismforstoringwater–snow–issensiGvetowarming.

The Cascade and Olympic Mountains have the highest fraction of “warm snow” (snow falling between 27-32°F) in the continental U.S. (Mote et al. 2008)

April1stSnowpack:

•  Since1950:about−25%

•  2080s,averageprojec*on:−37to−55%.

Historical

Samish River

Oct Dec Feb Apr Jun Aug

Rain dominant (Green)

Snohomish River

Mixed rain and snow (Red)

Sauk River

Snow dominant (Blue)

Snow has a major effect on streamflow.

HistoricalA1B 2040s

Samish River

Snohomish River

Sauk River

HistoricalA1B 2040sA1B 2080s

Samish River

Snohomish River

Sauk River

Snowkeepswateroutoftheriverswhenwedon’twantit,andreleasesitwhenwedo.

WarmingStreamsBythe2080s:

•  WarmingStreams:+4.0°Fto+4.5°F,onaverage.

•  Numberofrivermilesexceedingthermaltolerancesareprojectedtoincreaseby>70mi.forsalmon,and>170mi.forchar Datasource:NorWeST,

Figure:ClimateImpactsGroup

Early peak flows

Floods

OA? SSTs?

Warm, low streamflow

Salmon Impacted Across Full Life-Cycle

EvaluaGngtheEffecGvenessofRestoraGonAcGons

Figuresource:Ba.netal.2007

yearling migrants primarily spawn in the upper watershed (16),where climate impacts are projected to be greatest.

Chinook salmon exhibit remarkable plasticity in many life-historytraits and may be able to respond evolutionarily or behaviorally toclimate change in ways not captured in our models. Our findings donot support the notion that fish will react to climate change bymoving to higher elevations (17), but they may be able to mitigatetemperature effects by sheltering in thermal refugia when temper-atures become too high (18). Although their need to lay eggs inareas of high subgravel flows (19) makes it unlikely that Chinook

could alter redd placement to avoid the effects of higher peak flows,changes in the timing of migration, egg laying, and other life stagesmay allow fish to prosper in altered habitats. More southerlypopulations of Chinook, which migrate and spawn later in the year,may provide a model for how Puget Sound populations will respondto warming, but climate change also may produce conditions unlikeanything currently experienced by salmon. Little is known about thecapacity of salmon to adjust to climate change, and the potential forevolutionary or behavioral responses is one of the most importantavenues for future research.

Habitat restoration can play an important role in offsetting theeffects of climate change, although our results suggest that mostexpected climate impacts cannot be mitigated entirely. In relativelynarrow streams, reforestation may decrease water temperatures byincreasing shading, but in wide, main-stem reaches where mostChinook salmon spawn, riparian vegetation has a minor effect onwater temperature. New reservoirs and flood-control structurescould mitigate flow impacts, but because these effects are likely tobe most severe in headwater streams, it is unlikely that such actionswould be feasible or desirable. As in many river basins, thehighest-elevation portions of the Snohomish watershed, whereprojected climate impacts are greatest, are largely protected andpristine, with little potential for further restoration. Although directmitigation of the hydrologic impacts of climate change may not bepossible, habitat restoration, particularly the restoration of juvenilerearing capacity, may benefit salmon populations threatened by

Fig. 3. Climate impacts on three hydrologic variables. (A1–A3) The results ofthe GFDL R30 climate model. (B1–B3) The results of the HadCM3 model. (Top)Percent change in incubation peak flow. (Middle) Percent change in minimumspawning flow. (Bottom) Change in prespawning temperature in degreesCelsius. The basin-wide average change is shown in the lower left corner ofeach figure. Black lines delineate subbasin boundaries. All simulations usedthe ‘‘current’’ land use scenario.

Fig. 4. Basin-wide percent change from 2000 in numbers of spawningChinook under different combinations of climate change and habitat resto-ration for the GFDL R30 (A) and HadCM3 (B) climate models.

Fig. 5. Change in spawning Chinook salmon abundance between 2000 and2050 under three future land-use scenarios. (A1–A3) The results of the GFDLR30 climate model. (B1–B3) The results of the HadCM3 model. (Top) Currentland-use scenario. (Middle) Moderate restoration scenario. (Bottom) Full res-toration scenario. The basin-wide total change appears in the lower leftcorner of each figure.

Battin et al. PNAS ! April 17, 2007 ! vol. 104 ! no. 16 ! 6723