Climate Change in the Chehalis River and Grays Harbor Estuary · 2013. 4. 4. · (model A1FI,...

Climate Change in the Chehalis River and Grays Harbor Estuary

Prepared for the Chehalis Basin Habitat Work Group

February, 2013

Prepared by Wild Fish Conservancy Dr. Todd Sandell and Andrew McAninch

Grays Harbor Juvenile Fish Use Assessment, 2011 Wild Fish Conservancy Page 2

Contents Anticipating the Effects of Climate Change ................................................................................... 2

1.1: Climate Change on the Global Scale ................................................................................... 2

1.2: Climate Change in the State of Washington ........................................................................ 8

1.3: Climate Change in the Chehalis River Basin and Grays Harbor Estuary .......................... 12

1.4: Effects of Climate Change on Salmon in the Chehalis River Basin .................................. 14

1.5: Modeling Sea Level Rise in the Grays Harbor Estuary ..................................................... 19

References ..................................................................................................................................... 41

Anticipating the Effects of Climate Change

1.1: Climate Change on the Global Scale

The latest Intergovernmental Panel on Climate Change report (IPCC: 2007)

confirms the findings of earlier panels and predicts that ocean temperatures and sea

levels will continue to rise through the 21st century as a result of anthropogenic carbon

(CO2) production. From 1961-2003, global ocean temperatures have risen by 0.10°C

from 700m in depth to the surface (Figure 1; Pacific Northwest, USA circled in red); from

1993-2003, the rate of warming increased, but has slowed since 2003 (Bindoff et al.

2007). Global sea level rise increased during the 20th century at an average rate of 1.7 ±

0.5 mm/year (Figure 2), and there is evidence that this rate has accelerated in recent

years (1961-2003), with an average increase of 1.8 ± 0.5 mm/year. The increase in sea

level is primarily the result of two factors, the thermal expansion of warming sea water

(accounting for 0.4 ± 0.1 mm/year from 1963-2003; Figure 1) and the input of melt

water from glaciers, ice caps at the poles and the major ice sheets (Greenland and

Antarctica). For the more recent period of 1993-2003, the estimates are more precise

due to improved technology (mainly satellite observations of sea surface height) and the

contribution from thermal expansion (1.6 ± 0.5 mm/year) and melt water combined was


2.8 ± 0.7 mm/year. However, these two factors (and other minor inputs deemed to be

inconsequential on the global scale) do not match the observed rise in sea levels; thus,

the models currently in use underestimate observed global sea level rise and therefore

lend uncertainty to predicted sea level rise by 2100. Of the several different predictive

models presented in the IPCC review, the model “A1B” is commonly cited as it

represents a moderate scenario for ocean warming and sea level rise. The A1B model

values for air temperature increase range from 1.7°C to 4.4°C (~3 to 8°F); for sea level

rise, the values range from 21cm to 48cm (Bindoff et al. 2007). The worst-case scenario

(model A1FI, calculated under a scenario of no significant reduction in greenhouse gas

emissions) predicts that air temperature will increase by 2.4 to 6.4°C (4.3 to 11.5°F) and

sea levels will rise from 26cm to 59cm.

Figure 1: Linear trends in the change of ocean heat content from 1955-2003.

Reproduced from the original 2007 IPCC report, where it was figure 5.2.

These effects, both observed and predicted, are not evenly distributed on the global

scale. The Pacific Ocean is characterized by warming, but recent cooling also occurred in some


regions of the eastern Pacific, namely the region extending from 32°N to 48°N (note that Grays

Harbor is at ~47°N) (Figure 1; Pacific Northwest circled in red). This cooling may be the result of

a reversal in the Pacific Decadal Oscillation (PDO) (Bindoff et al. 2007). Regional differences are

also apparent in the sea level data; in the Pacific Northwest, oceanographic factors including

shifts in ocean circulation (seasonal and annual) and atmospheric pressure associated with the El

Niño Southern Oscillation (ENSO) and Aleutian low (an area of low pressure that moves from the

Aleutian Islands into the Gulf of Alaska in the winter, influencing storm tracks) are largely

responsible (the IPCC report cites an approximately 10 mm rise and fall mean sea level during

the 1997–1998 ENSO event) (Bindoff et al. 2007). In the eastern Pacific Ocean (including along

the Pacific Northwest coast) sea level has declined in the short term (Figure 2), but is has still

risen in comparison with historical levels (“long-term trends”, Figure 3). It is important to note

that, due to the lack of data, the 2007 IPCC report models do not factor in the instability of the

major ice sheets, and as a result sea level rise may exceed the predictions of scenario A1B (Stocker

et al. 2010).


Figure 2. (a) Geographic distribution of short-term linear trends in mean sea level (mm yr–1) for 1993

to 2003 based on TOPEX/Poseidon satellite altimetry (updated from Cazanave and Nerem, 2004) and

(b) geographic distribution of linear trends in thermal expansion (mm yr–1) for 1993 to 2003 (based on

temperature data down to 700 m from Ishii et al., 2006). Modified from the original (Figure 5.15a from

the 2007 IPCC report); the Pacific Northwest is circled in red.


Figure 3. (a) Geographic distribution of long-term linear trends in mean sea level (mm yr–1) for 1955

to 2003 based on the past sea level reconstruction with tide gauges and altimetry data (updated from

Church et al., 2004) and (b) geographic distribution of linear trends in thermal expansion (mm yr–1) for

1955 to 2003 (based on temperature data down to 700 m from Ishii et al., 2006). Note that colours in

(a) denote 1.6 mm yr–1 higher values than those in (b). Modified from the original (Figure 5.15b from

the 2007 IPCC report); the Pacific Northwest is circled in red.


Along with these predictions, more general effects on climate are also noted. The

occurrence of extreme high tides, the intensity of hurricanes and typhoons (which are likely to

generate greater storm surges), and an increase in the number of heavy precipitation events are

all expected (Bindoff et al. 2007), though they will vary by region. Changes in ocean salinity have

also occurred, with the north Pacific Ocean (above 50°N) freshening (decreased salinity in the

upper 500m) due to the addition of melt water from glaciers and the Arctic ice cap, though

predictions of the extent of these changes are not available at this time, due in part to differing

effects at regional and local scales and uncertainty about the stability of ice sheets and the

Arctic ice cap (Bindoff et al. 2007; Stocker et al. 2010). Changes in precipitation are also

expected, with warmer air carrying more evaporated moisture from the subtropics towards the

poles in both hemispheres. Due to the increase in moisture, rainfall is expected to increase on

the windward slopes of mountain ranges in North America as the air is pushed upward by the

mountains, cools, and condenses. Precipitation during the cold season is expected to increase in

the northern Rocky, Cascade, and Sierra Nevada mountain ranges (up to 10%), though mean

annual precipitation may decline (Christensen et al. 2007). A decrease in snow depth (“snow

pack”) is also predicted despite increased winter precipitation, due to delays in autumn snowfall

and earlier spring snowmelt associated with generally warmer air temperatures. However, the

increased snowfall could “more than make up for” the shorter snow season and yield increased

snow accumulation in some regions (Christensen et al. 2007).


Figure 4. Regional temperature anomalies for North America (Figure 11.11 in the

original 2007 IPCC report).

1.2: Climate Change in the State of Washington

In 2009, the Washington Climate Change Impacts Assessment Group issued a

report on climate change predictions for the state. Using higher resolution regional

models, they predicted an annual average increase in air temperature of 1.7°C (3.2°F)

by the 2040s and 2.9°C (5.3°F) by the 2080s (compared to temperatures from 1970-

1992) (Figure 4) (Littell et al. 2009). Sea level rise by the year 2100 is projected to be in

the range of 5-33cm (2-13 inches) under the moderate models for Washington state

(similar to the A1B global climate model), with the possibility of much larger increases

(as high as 89-127cm (35-50 inches)) if the Greenland ice sheets collapse, depending

on location. The report emphasizes that there will likely be substantial variation


within different regions of the state caused by local winds (in western Washington,

typically higher on the coast and Strait of Juan de Fuca) and vertical land movement

(the Olympics mountains continue to rise as a result of plate tectonics at a rate of

~2mm per year (Huppert, Moore, and Dyson 2009). In comparison with the historical

average (1916-2000), spring snowpack (April 1st) is predicted to decrease statewide

by 28% by the 2020s, 59% by the 2040s, and 59% by the 2080s (Littell et al. 2009).

This is likely to cause significant changes in seasonal river and stream water flow,

particularly for “transient” river systems, where water is input as a mix of rain and

snowmelt (typically at moderate elevations, e.g. Yakima River), with expected

increases in total snowmelt and decreased summer flows (Figures 5, 6). “Snowmelt

dominant” systems (typically higher elevation basins or basins that have high

elevation headwaters (e.g. the Columbia River)), which receive most of their winter

precipitation as snow, will also be affected. State hydrological models predict that by

the 2080’s no snowmelt dominant systems will remain; ten formerly snowmelt

dominant basins at high elevations in the North Cascades will become transient

basins (Mantua, Tohver, and Hamlet 2009; Mantua, Tohver, and Hamlet 2010). The

final category, “rain dominant” river systems (e.g. coastal rivers, including the

Chehalis River), will be the least impacted, although an increase in the magnitude

and frequency of extreme winter precipitation events is predicted, which will increase

winter stream flows and may increase flooding (Figure 6). Finally, the regional, high

resolution climate models specific for Washington State suggest that some localities

may experience very different patterns in temperature and precipitation than those

predicted for western North America region by global climate models.


Figure 5. Differences between a regional climate model (WRF) and a global climate model (CCSM3)

for projected changes in fall precipitation (September to November top) and winter temperature

(December to February, bottom) for the 2040s. The global model produces a regionally averaged

11.7% increase in precipitation, but the regional model provides more detail (top), projecting some

areas of increase (green) and some of decrease (brown) compared to the global model. Note that

large increases are seen on windward (west and southwest) slopes and smaller increases on leeward

(east and northeast) slopes. The global model produces a 3.6°F statewide averaged increase in winter

temperature, while the regional model produces a statewide average 2.6°F warming. There are greater

increases (darker red) at higher elevations and windward slopes, particularly the Olympic Mountains,

North Cascades, and central Cascades. These differences illustrate the value of regional climate

models for identifying sub-regional patterns and differences. The patterns of climate change differ

depending on the global model being downscaled (we present only one here); nevertheless, the local

terrain has a consistent influence on the results. (Figure 4 in the original 2009 WA climate report; page

7)


Figure 6. Historical and projected future hydrographs for three rivers under the medium emissions

scenario (A1B). The Chehalis River represents a rain-dominated watershed, the Yakima River

represents a transient watershed (mixed rain and snow), and the Columbia River represents a

snowmelt-dominated watershed. Projected climate changes will influence the timing of peak stream

flow differently in different types of hydrologic basins. The timing of peak stream flow does not

change in rain-dominated basins because most of the precipitation falls as rain, both currently and in

the future, and is therefore available for runoff as it falls. Timing of peak flow shifts earlier as climate

warms in the transient and snowmelt-dominated basins because precipitation that historically fell as

snow later falls as rain – snowpack melting ceases to dominate the timing of peak flow as the

snowpack declines (Figure 6 in the original WA state climate report; page 9).


1.3: Climate Change in the Chehalis River Basin and Grays Harbor Estuary

The predicted shifts in climate will have a number of effects on the Washington

coast:

1) Inundation. As the sea level rises (Mote, et al. 2008), the lowest lying

shores will be regularly flooded by high tides. Coastal inundation is a

gradual process on decadal time scales due to expanding volume of

ocean water (called eustatic SLR), melting of glaciers, and local factors

such as land subsidence and tectonic uplift (Snover et al., 2007).

2) Flooding. During major storm events, SLR will compound the effects of

storm surges, which can contribute to more extensive coastal flooding.

Also, changes in the seasonal pattern of rainfall or increased peak runoff

from snow melting could lead to more serious coastal flood events,

especially near rivers.

3) Erosion and Landslides. Although erosion on beaches and bluffs is a

natural, on-going process, major episodes of erosion often occur during

storm events, particularly when storms coincide with high tides. SLR will

exacerbate the conditions that contribute to episodic erosion events, and

this will accelerate bluff and beach erosion. Increased storm strength or

frequency will exacerbate this. Climate change is also likely to increase

winter precipitation in the Pacific Northwest, which can contribute to

landslides on bluffs saturated by rainfall or run-off.

4) Saltwater Intrusion. As the sea level rises, coastal freshwater aquifers will

be subject to increased intrusion by salt water.

5) Increased Ocean Surface Temperature and Acidity. As the atmosphere

warms, the ocean temperatures will increase. Additionally, absorption of

carbon dioxide by the oceans leads to increasing acidity (lower pH).

(Huppert, Moore, and Dyson 2009)

Here we will focus on changes in sea level, precipitation and stream flow, and the

likely effects on salmon in the Chehalis Basin and Grays Harbor estuary. The entrance

to Grays Harbor is within the northern part of the Columbia River littoral (nearshore)

cell; the plume of water from the Columbia extends North (particularly in winter) and,

historically, transported sediment into Grays Harbor. The construction of jetties at


the mouths of the Columbia River and Grays Harbor limited this influx of sediment,

but did encourage rapid sediment accretion adjacent to the jetties through the

1950’s. However, since the construction of the hydropower system on the Columbia

River, sediment transport has been greatly reduced. The Southwest Washington

Coastal Erosion Project has identified several areas (“hot spots”) where erosion is a

concern, primarily caused by the loss of sediment transport, gradually rising sea

levels, and a northward shift in the tracks of winter storms (as a result of broader

global climate change). In the Grays Harbor area, these hot spots are just North of

the northern jetty (Ocean Shores) and at the north entrance of Willapa Bay, which

has lost an average of 19.7m (65 ft.) of beach per year since the 1880s (Huppert,

Moore, and Dyson 2009). If winter storms intensify, as predicted by the climate

models, coastal erosion will intensify. Previous efforts to limit erosion at Ocean

Shores are unlikely to reverse this trend:

“Ironically, shoreline armoring by sea walls, riprap, or revetments

typically decreases the volume of sediment available to sustain

beaches. Because wave energy reflected off coastal armor carries

sediment offshore, and the armoring itself reduces erosion of protected

bluffs, protected shores gradually lose sediment and shallow water

habitat (Johannessen and MacLennan, 2007, p.13.). The resulting

increased water depths and greater wave energy tends to weaken the

protective structures.” (Huppert, Moore, and Dyson 2009)

The interior of Grays Harbor (Willapa Bay is similar) is dominated by mud flats and is

relatively protected from high energy waves. However, the area occupied by mud flats in Grays

Harbor has declined, possibly due to the increased currents flowing through the jettied

entrance at the mouth, which allows more wave energy to enter the estuary.

Sea level rise will move the shoreline landward both within and outside of Grays Harbor.

Predictions for Washington state are given as relative sea level rise (rSLR) because in some areas


(Olympic Peninsula) the land is rising, while in others (Puget Sound) it continues to fall; rSLR is

the difference between land movement and sea level rise. The area around Grays Harbor is

relatively stable, with less than 1mm/year of land elevation change (Huppert, Moore, and Dyson

2009). For the southern Washington coast (including Grays Harbor), rSLR is estimated to rise in

the range of 3-45cm (1-18”) by 2050 and by 6-108cm (2-43”) by 2100 (see Table 1, below) (Mote

et al. 2008). The authors note that the rSLR estimates are provided for advisory purposes and are

not actual predictions because the current models are not deemed fully reliable, the

probabilities have not been formally quantified, and SLR cannot be accurately predicted for

specific locations.

Table 1: Relative sea level rise (rSLR) projections under 3 different severity models for

major geographic areas of WA state (reproduced from Mote et al., 2008, where it

was Table 2)

By 2050 By 2100

SLR Estimate

NW Olympic Peninsula

Central & Southern

Coast

Puget Sound

NW Olympic

Peninsula

Central & Southern

Coast Puget Sound

Very Low -12cm (-5”) 3cm (1”) 8cm (3”) -24cm (-9”) 6cm (2”) 16cm (6”)

Medium 0 12.5cm (5”) 15cm (6”) 4cm (2”) 29cm (11”) 34cm (13”) Very High 35 cm (14”) 45cm (18”) 55cm (22”) 88cm (35”) 108cm (43”) 128cm (50”)

1.4: Effects of Climate Change on Salmon in the Chehalis River Basin

As has been frequently pointed out, salmon are affected by the various aspects of

climate change at every stage of their life cycle; however, these changes will have varying effects

on different stocks due to life history variation and location. The Washington Climate Impacts

Group (CIG) focused on “hydroclimate”: how seasonal low flows, stream temperatures during the

warmer months, and the timing and volume of peak flows due to climate change are likely to

impact salmon. Increasing stream temperatures are likely to reduce freshwater habitat,

particularly in summer, because salmon are stressed by water temperatures above ~17.4°C

(64°F), varying by species (Mantua, Tohver, and Hamlet 2009). Average temperatures in excess

of 21°C (70°F) can pose a barrier to migration; prolonged exposure to temperatures at or above

this mark can be lethal in both adults and juveniles. Temperatures above 15°C (59°F) can also

place salmon at a competitive disadvantage with warm water species (both native and


introduced, e.g. largemouth bass) and lead to higher predation. In the CIG report, areas where

predicted maximum weekly water temperatures exceeded the thermal limits for salmon were

classified as “lost habitat”; estimates ranged from 5-22% of salmon habitat lost statewide by

2090 under the various climate model scenarios used to predict warming (Mantua, Tohver, and

Hamlet 2009).

The amount and timing of stream flow is also a critical consideration for salmon.

Excessive flows can lead to stream bed scouring, removing spawning habitat for egg

deposition, as well as the loss of in-channel large woody debris that serves to mitigate

flow and provide a refuge for juveniles. The CIG report cites research by Battin (2007) in

the Snohomish River basin on spring/summer (ocean-type) Chinook salmon that found

projected extreme high flows would have the most deleterious effect on reproductive

success (Mantua, Tohver, and Hamlet 2009). For coho salmon, freshwater survival was

most heavily affected by (1) in-stream temperatures during their first summer, in

combination with the availability of deep pools with cooler water at the bottom, and (2)

water temperatures during their second winter, combined with off-channel refugia (e.g.

beaver ponds, backwaters) that provided areas with warmer water and decreased flows.

The combination of reduced summer flows and increased water temperatures are thus

particularly problematic for coho salmon (Beechie et al. (1994) and Reeves et al. (1989),

cited in (Mantua, Tohver, and Hamlet 2009)).

More generally, stocks of salmon with extended freshwater rearing periods will

be more sensitive to the predicted climate changes in freshwater (these include

steelhead and coho and fall (ocean type) Chinook salmon). Mortality rates for adult

salmon with summer spawning migrations are also expected to increase. In western

Washington, changes in the availability of quality rearing habitat due to warmer

temperatures is predicted to affect mainly summer and winter run steelhead and coho

salmon (Mantua, Tohver, and Hamlet 2009). Because the Chehalis River is a rainfall

dominant system, alterations to the effect of seasonal snowpack and the hydrocycle


(timing of runoff) are expected to be minimal (Figure 5, above) in comparison with

transient and snow-dominated basins in the state. Of the major tributaries, only the

Humptulips and (to a lesser extent) Satsop Rivers receive snowmelt from the Olympic

mountains; these rivers are expected to transition into fully rainfall dominant systems as

regional air temperatures increase as a result of climate change. The Chehalis basin is

predicted to have stressful (but not lethal) summer water temperatures by 2040 (Figure

5) (Mantua, Tohver, and Hamlet 2009). In the tributaries, particularly those without cool

groundwater seepage and/or with decreased riparian tree cover as a result of logging or

other disturbances, summer water temperatures may rise into the critical zone for

salmon, rendering these areas unviable rearing grounds. The report recommends

mapping areas of thermal refugia as one of the key steps in anticipating climate change

and mitigating the effects on salmon.

Figure 7. August mean surface air temperature (colored patches) and maximum stream

temperature (dots) for 1970-1999 (left) and the 2040s (right, medium emissions scenario,

(A1B)). The area of favorable thermal habitat for salmon declines by the 2040s in western

Washington, and in eastern Washington many areas transition from stressful to fatal for

salmon. Circles represent selected stream temperature monitoring stations used for

modeling stream temperatures. (Figure 9 in the original report; (Mantua, Tohver, and Hamlet 2009))


The CIG report did not specifically consider the effects of climate change on

Washington’s estuaries, and most of the IPCC studies on estuaries considered only those

bordering the Atlantic Ocean. However, studies on the Columbia River estuary and nearshore

(ISAB, 2007 and others) provide some information that pertains to Grays Harbor. Changes in the

volume and temperature of the river water entering the estuary will clearly modify the extent of

salt water intrusion and stratification in the estuary. Increased water flows in the winter (due to

predicted increases in precipitation) will likely lead to increased stratification, with the less dense

freshwater overlaying the denser salt/brackish component. However, a warmer ocean could also

result in a less dense salt wedge that would not intrude as far into the estuary. This may have

important ramifications for the location of the estuary turbidity maximum, the region at the

leading edge of the salt wedge characterized by high bacterial production and increased

concentrations of prey items utilized by juvenile salmon (e.g. harpacticoid copepods) (ISAB

2007).

Changes to the Chehalis River flow regime are also likely to modify the habitat

availability in the estuary. Low elevation sand and mud flats and floodplains are likely to be

inundated more frequently during the higher winter precipitation regimes predicted. In winter,

the amount of plant detritus flushed into the estuary from riparian and emergent marsh areas

could increase, providing more energy to the food web (though fewer salmon utilize the estuary

in winter). Reduced summer flows would have the opposite effect. Rising sea levels could offset

the increase in detrital input from tidal marsh and freshwater riparian areas by permanently

covering mud flats, which are detrital producers, reducing the net input of nutrients into the

estuarine food web. Only a significant increase in sediment transport would maintain the mud

and sand flats; this is unlikely under present scenarios (construction of a dam on the mainstem

Chehalis would further reduce sediment input into the estuary, accelerating the loss of mud and

sand flats). An increase in the strength and frequency of winter storm events, as predicted,

would lead to higher wind-driven wave energies along the coast and near the estuary mouth,

and could undercut terraces along the shoreline and undermine restoration projects that utilize

dredged sand (ISAB 2007).


The effect of these changes on salmon in the estuary again varies by species and life

history, but some factors will affect all of the salmon species present. During the adult phase,

when salmon are returning to spawn, increased freshwater temperatures in the tributaries could

result in adults holding in the estuary awaiting cooler temperatures. This has been shown to

increase mortality due to stress and disease among salmon in B.C. (Johnson et al., 1996) and in

the Klamath River (OR and CA; California Department of Fish and Game 2003; cited in (ISAB

2007)). There are also a number of effects on juvenile salmon, primarily the result of

temperature. In Grays Harbor, juvenile Chinook salmon have the longest estuary residence times

(see the WFC Grays Harbor project annual reports), and an increase in water temperature would

affect their growth and metabolism, potentially increasing the demand for food and increasing

competition between salmon species, hatchery and wild salmon, and salmon and other fish

species (ISAB 2007). Warmer water temperatures may also reduce the influx of cool-water

species (e.g. herring, anchovy) into the estuary from the ocean in spring and summer. A

reduction in the number of baitfish that are of a similar size to smolts, but typically much higher

in abundance, may result in increased piscine and avian predation on juvenile salmon (ISAB

2007). An effort to model the effect of environmental conditions on juvenile coho salmon

marine survival (Logerwell et al. 2003) in the Oregon production area found that lower spring

sea level anomalies were correlated with increased coho survival in the nearshore. In this case,

reduced sea levels were the result of strong southward along-shore winds and currents

combined with offshore transport of the water mass, which leads to the upwelling of nutrient-

rich water to the surface and increases primary and secondary production (Logerwell et al. 2003).

Anticipating the effect of climate change was not part of this study, but higher sea levels,

changes in water temperature, salinity, and regional and global shifts in atmospheric and

oceanic circulation could alter the frequency and duration of upwelling events, negatively

impacting coho salmon.

The options for mitigating the effects of these are varied, but place salmon and people at

odds with one another over water usage. Since water temperature and stream flow are critical to

salmon survival, reducing alterations to these should be a priority. Management actions should

focus on “restoring floodplain functions that recharge aquifers, identifying and protecting

thermal refugia provided by ground-water and tributary inflows, undercut banks and deep


stratified pools, and restoring vegetation in riparian zones that provide shade and complexity for

stream habitat. Restoring, protecting, and enhancing instream flows in summer are also key”

(Logerwell et al. 2003). Freshwater salmon habitat, particularly those areas that provide off-

channel refugia from high flows (in the lower Chehalis River, exemplified by the tidal surge plain)

need to be protected and enhanced. Other strategies include the retention of forest cover to

limit stream warming, particularly in riparian corridors, and reducing the expansion of

impervious surfaces that accelerate runoff and contribute to high flows (Booth and Jackson

1997, cited in (Logerwell et al. 2003)). As temperatures warm, thermal refugia are likely to

become restricted to headwater reaches during the summer; protection of these areas, as well as

reconnecting fish access by removal of barriers to passage (e.g. culverts) will be important. In the

estuary, increases in sea level will lead to inundation of lower elevation areas; planning for land

acquisition and protection of these sensitive areas, rather than disruptive alterations (e.g.

shoreline armoring, dikes, and levees) will be essential in helping offset habitat loss. Finally,

climate changes will alter the selective pressures among salmon species and life histories; those

utilizing spring or fall/winter for rearing, migration and spawning are likely to fair better than

those dependent upon doing so in summer, when temperatures will be at their peak and water

flows reduced. The changes predicted to occur by 2100 are rapid on the evolutionary time scale,

and salmon will be challenged to adapt. The maintenance of salmon life history diversity, a key

to resilience, is paramount.

1.5: Modeling Sea Level Rise in the Grays Harbor Estuary

To better understand what these predicted changes in sea level rise (SLR) will

mean for habitat availability in Grays Harbor in the future, we applied three different

scenarios of SLR to the tidal portions of the estuary. Preliminary sea level rise (SLR)

modeling was conducted using the Sea Level Affecting Marshes Model (SLAMM), which

“simulates the dominant processes involved in wetland conversions and shoreline

modifications during long-term sea level rise.” SLAMM uses a digital elevation model

(DEM) and National Wetlands Inventory (NWI) based habitat classification as the basis


for its modeling. We used a 2009 Light Detection and Ranging (LIDAR) elevation model

of Grays Harbor that was flown by the Federal Emergency Management Agency (FEMA)

and obtained from the Puget Sound LIDAR Consortium. The Grays Harbor estuary was

previously modeled using SLAMM by Warren Pinnacle Consulting, Inc. for Ducks

Unlimited in 2010; however, their analysis used the 10 meter DEM for the majority of the

harbor, resulting in considerable uncertainty in the model output in low relief areas. We

wanted to redo this modeling using the more accurate and precise LIDAR DEM (2009),

which has a one meter resolution cell size. The size of the DEM for the whole of the

Grays Harbor estuary was too large for the SLAMM software to process, so the DEM was

resampled to a 5m cell size so that the SLAMM software could process the data.

The National Wetlands Inventory (NWI) wetlands data were reclassified into

SLAMM categories using the classification described in the SLAMM technical

documentation, available at:

http://warrenpinnacle.com/prof/SLAMM6/SLAMM6_Technical_Documentation.pdf.

Since the SLAMM is designed to work with the NWI data, the model starts simulating

from the date that the NWI data was created, 1981, and uses recent, known sea level

rise (SLR) for the historic portion of the simulation. We chose to simulate three SLR

scenarios based on current predictions. First, we simulated the IPCC A1B maximum

scenario, which is 59cm sea level rise by 2100. Since current scientific opinion seems to

be in agreement that the IPCC predictions are low and it is likely that the actual SLR will

be significantly higher (due to rapid melting of ice sheets), we also simulated a rise of

75cm and 1 meter so that the projections are still applicable if SLR is higher than the

A1B scenario predicts (Figures 10 and 11, below). The changes in habitat area (hectares)

are summarized in Table 2 (below) as well as in Table 3, which shows the percentage

change in area.

The modeling that WFC performed was preliminary and has some limitations.

First, we did not delineate the existing dikes in Grays Harbor (particularly in the

http://warrenpinnacle.com/prof/SLAMM6/SLAMM6_Technical_Documentation.pdf


Humptulips River flood plain) and therefore the model does not take these into account.

Additionally, the data set available did not include bathymetric (underwater) elevations

and therefore the model doesn't model habitat changes in the flats and open water

habitats very precisely. We will investigate the possibility of including these data, if they

are available with enough precision, in future reports. Second, the NWI data does not

perfectly match our study plan habitat classifications (e.g. NWI identifies both tidal and

freshwater swamps, while our simpler habitat categories may refer to these areas as

“forested”, as in much of the surge plain). As a disclaimer, the model outputs are only

projections and should not be used for specific predictions at any one area or point in

time.


Figure 8: Grays Harbor estuary initial habitat classifications from the 1981 National Wetland Inventory study (1981)


Figure 9a: Estimated habitat changes in Grays Harbor estuary in 2025 under the IPCC projection A1Bmax sea level rise by 2100


Figure 9b: Estimated habitat changes in Grays Harbor estuary in 2050 under the IPCC projection A1Bmax sea level rise by 2100


Figure 9c: Estimated habitat changes in Grays Harbor estuary in 2075 under the IPCC projection A1Bmax sea level rise by 2100


Figure 9d: Estimated habitat changes in Grays Harbor estuary in 2100 under the IPCC projection A1Bmax sea level rise


Figure 10a: Estimated habitat changes in Grays Harbor estuary in 2025 with an increase of 75cm in sea level rise by 2100


Figure 10b: Estimated habitat changes in Grays Harbor estuary in 2050 with an increase of 75cm in sea level rise by 2100


Figure 10c: Estimated habitat changes in Grays Harbor estuary in 2075 with an increase of 75cm in sea level rise by 2100


Figure 10d: Estimated habitat changes in Grays Harbor estuary in 2100 with an increase of 75cm in sea level rise


Figure 11a: Estimated habitat changes in Grays Harbor estuary in 2025 with an increase of 100cm in sea level rise by 2100


Figure 11b: Estimated habitat changes in Grays Harbor estuary in 2050 with an increase of 100cm in sea level rise by 2100


Figure 11c: Estimated habitat changes in Grays Harbor estuary in 2075 with an increase of 100cm in sea level rise by 2100


Figure 11d: Estimated habitat changes in Grays Harbor estuary in 2100 with an increase of 100cm in sea level rise


Table 2: Comparison of habitat area (in hectares) in the Grays Harbor estuary under varying

model predictions of sea level rise (SLR). The A1B model (~59cm SLR max) is the

moderate climate change scenario from the 2007 IPCC report; also shown are changes

if sea level rises 75cm and 100cm by 2100 in comparison to the 1981 data.

Table 3: Comparison of percent change in habitat areas in the Grays Harbor estuary under

varying model predictions of sea level rise (SLR). The A1B model (~59cm SLR max) is

the moderate climate change scenario from the 2007 IPCC report; also shown are

changes if sea level rises 75cm and 100cm by 2100 compared to 1981 data. Both the

NWI habitat categories and the approximate equivalent habitat from our sampling plan

are provided. Note that percent changes >100% are listed as multiples (e.g. “3x”);

percentages of less than 100% indicate a net loss in that habitat type.

Area in Hectares (Ha)

NWI habitat categories 1981 (Ha) A1B (Ha) % of 1981 75cm (Ha) % of 1981 1 m (Ha) % of 1981

Dry Land 32,788.9 28,802.9 88 28,665.2 87 28,101.0 86

Nontidal Swamp 1,544.0 660.3 43 635.7 41 529.2 34

Inland Fresh Marsh 788.3 355.6 45 346.3 44 306.1 39

Tidal Fresh Marsh 327.3 36.2 11 31.6 10 18.3 6

Transitional Marsh / Scrub Shrub 13.9 3,692.6 26532 3,671.4 26380 2,773.4 19928

Regularly Flooded Marsh (Saltmarsh) 1,109.5 2,674.1 241 2,873.3 259 4,523.6 408

Estuarine Beach 265.3 179.6 68 176.9 67 131.4 50

Tidal Flat 14,926.6 2,481.3 17 2,489.4 17 2,554.7 17

Inland Open Water 106.3 56.4 53 55.2 52 51.7 49

Riverine Tidal Open Water 656.5 49.3 8 48.8 7 45.9 7

Estuarine Open Water 8,664.5 22,260.0 257 22,274.4 257 22,392.1 258

Irregularly Flooded Marsh 408.7 2,497.6 611 2,487.8 609 2,361.5 578

Inland Shore 67.6 61.6 91 61.1 90 52.5 78

Tidal Swamp 2,209.3 69.2 3 59.7 3 35.2 2

Sea Level Rise


Note that in Table3 we provide the rough equivalent of the NWI habitats from our habitat

categories. Several of these are fairly clear (e.g. “tidal flat” is equivalent to our sand and mud

flats), but the “estuary open water” category from the NWI classifications is not easily broken

down into areas of depth (open water) and those shallower areas that are likely to support

aquatic vegetation beds, which are productive and critical for juvenile fish. Hopefully the

inclusion of bathymetric data in the future will help resolve these two categories.

Several trends are immediately obvious from the changes depicted in figures 8-11. In the

central estuary and North Bay (and to a lesser extent South Bay), there will be extensive loss of

low elevation tidal mud and sand flats (roughly 83% lost; Table 3) (Figure 12). Under the A1B

scenario this is predicted to occur by 2075; under the 75cm and 1 meter scenarios, by 2050.

Both Goose and Sand Islands are submerged by increasing sea levels by 2100 (A1B and 75cm

scenarios) or 2075 (1 meter scenario). In the inner estuary zone, the extensive mud flats around

Moon Island (near the airport) and Rennie Island are submerged by 2075 in all three scenarios,

although inundation of Rennie Island itself is not predicted. The area of the Grays Harbor

National Wildlife Refuge (USFWS), adjacent to Moon Island, fares better, though some area will

still be lost. Note that maintenance of mud and sand flats is dependent upon sediment

deposition in the estuary; if the dam currently under discussion for the Chehalis River near

Amount of change

NWI habitat categories Our Habitat Category A1B 75cm 1m

Dry Land Dry Land 88% 87% 86%

Nontidal Swamp Forest 43% 41% 34%

Inland Fresh Marsh Scrub/Shrub Cover 45% 44% 39%

Tidal Fresh Marsh High Emergent Marsh 11% 10% 6%

Transitional Marsh / Scrub Shrub Scrub/Shrub Cover 265x 263x 199x

Regularly Flooded Marsh (Saltmarsh) High Emergent Marsh 2.4x 2.6x 4.1x

Estuarine Beach Cobble/gravel/Sand beach 67.7% 66.7% 49.5%

Tidal Flat Mud Flat/Sand Flat 16.6% 16.7% 17.1%

Inland Open Water Open Water 53.1% 51.9% 48.6%

Riverine Tidal Open Water Open Water 7.5% 7.4% 7.0%

Estuarine Open Water Aquatic Vegetation Beds? 2.5x 2.6x 2.6x

Irregularly Flooded Marsh High Emergent Marsh 6x 6.1x 5.8x

Inland Shore 91.2% 90.4% 77.7%

Tidal Swamp Forest 3.1% 2.7% 1.6%

Sea Level Rise


Interstate Highway 5 is constructed, these habitats will be lost more quickly due reduced

downstream transport of sediment into the estuary.

Figure 12: Map of the Gray Harbor estuary, showing the sampling zones defined in the WFC

annual reports.

In the surge plain (Figure 12), the predicted changes in SLR will result in a rapid transition

from forested tidal swamp to irregularly flooded marsh by 2025 even in the most conservative

scenario (A1B); the net loss of forested area is predicted to be severe (~97% for the estuary as a

whole; Table 3). Many of the trees in this area will be claimed by the rising water levels and,

potentially, increased intrusion of the salt water wedge into the lower Chehalis River (the

changes in the extent of salt wedge intrusion are not covered by the model and are an area of

uncertainty). Under the higher SLR predictions, the area around Cosmopolis (currently protected


by tide gates) will also transition from dry land to transitional marsh by 2025 (all scenarios) and

eventually to tidal fresh water marsh (by 2050 under the 75cm scenario and between 2025 and

2050 under the 1 meter scenario). Aberdeen is predicted to undergo similar, but less dramatic,

transition, with transitional marsh beginning to appear around 2050 under the 1 meter scenario.

In North and South Bays, SLR will have less dramatic effects. Some areas of tidal flats will be

lost and there will be a reduction in the amount of forested area in the headwaters of the Elk

and Johns Rivers. However, most of these areas are expected to transition from one type of

marsh currently present (e.g. tidal fresh or transitional marsh) to salt marsh. In the estuary as a

whole, rising sea levels are predicted to dramatically increase the amount of the various types of

marsh land; for transitional marsh (scrub/shrub cover), over 200-fold; for regularly flooded salt

marsh, 2.5-4 fold; for irregularly flooded marsh, roughly 6 fold under all scenarios (Table 3). The

increase in salt water levels will result in a decrease in freshwater marsh habitat, with inland fresh

water marsh declining to ~45% of 1981 levels and tidal fresh marsh declining to roughly 10% of

1981 levels (Table 3).

Near the estuary mouth, the most noticeable changes will occur at Damon Point and the

Point Brown marsh (at the southern tip of Ocean Shores). The area of dry land at Damon Point

will decline under all scenarios by 2100, and almost no dry land will remain by 2100 under the 1

meter SLR scenario. The Point Brown marsh will transition from a majority of salt marsh (1981) to

a mix of salt marsh and transitional marsh by 2075 (A1B scenario) and by 2050 under the 75 cm

and 1 meter scenarios. The beach at Half Moon Bay, across the estuary mouth (southern shore),

will also be reduced and the dunes there may be subjected to increased wave energy and tidal

currents as SLR increases, potentially destabilizing the area (Scavia et al. 2002).

These changes will result in complex alterations in habitat availability and productivity for

the estuarine food web that are difficult to anticipate. Shellfish production will be adversely

impacted by the decline in the area of mud flats of appropriate depth (as well as by changes in

ocean acidification and other factors which are beyond the scope of this report). Bird species

reliant on estuaries will also be impacted, and in Grays Harbor, chick rearing areas on Sand

Island will eventually be inundated. Two important habitat types for juvenile salmon and other


fishes, eelgrass and aquatic vegetation beds, will also be altered, although the short-term

changes (prior to 2050) may not be negative (“eelgrass” is not a specific habitat type in the NWI

classification). A modeling study of eelgrass beds (and accessibility for feeding by the Brandt

goose) in Willapa Bay found that the area of eelgrass beds was likely to increase in the coming

decades as low elevation mud flats were inundated, providing habitat for eelgrass to occupy.

However, the long term outlook was for an eventual decline in the area available for eelgrass as

water depths increased and the waterline advanced to dikes (already in place), preventing the

formation of new shallow water areas optimal for eelgrass growth (Shaughnessy et al. 2012).

A review of climate change impacts on U.S. coastal ecosystems was conducted in 2002,

prior to the recent IPCC (2007) report; though the outlook has changed, with many climate

indices “ahead” of the predictions (e.g. ice sheet melting), several of their recommendations

remain valid. The preservation of estuarine habitats is essential for the species that depend on

them for survival, so it is critical that as sea level rises, new areas of habitat are available as the

waterline migrates landward. Extensive armoring of shorelines (dikes, levees, etc.) against sea

level rise may prevent this process from occurring, leading to the loss of wetlands and

undermining the biological and chemical processes that allow estuaries to be such productive

ecosystems (Scavia et al. 2002). To this end, development of vulnerable areas should be

prevented or discouraged, and setback lines from the coast and wetland margins should be

increased. Another option is the establishment of “rolling easements” which allow for

development that does not lead to the destruction of wetlands and beaches and are adjusted

according to local sea level rise over time.

For salmonids in particular, management strategies will also have to adapt. In theory,

harvest management is designed to produce sustainable yields, which are directly linked to the

productive capacity of the environment. As the environment is altered by climate change in

ways that do not favor salmon recruitment (e.g. warmer water temperatures, loss of thermal

refugia, decreased summer stream flows, etc.), harvest must be adaptively managed to maintain

sustainability. Exploitation and environmental change must be considered together to produce

strategies that allow these fish populations to remain sustainable (Scavia et al. 2002). As run


timing becomes increasingly important to offset increases in fresh water temperature, the

maintenance of salmon life history diversity will be critical. Stocks that return to spawn in the

summer or early fall will be most adversely affected; others will fare better in the Chehalis

system.

The scenarios predicted by climate change are sobering. However, advanced planning and

informed management provide solutions that can at least mitigate these changes and help

preserve the essential habitats that estuarine species rely upon. In Grays Harbor, shorelines

(particularly the southern shoreline, which overall has more areas at low elevation), the surge

plain, and the areas around the various sloughs and tributaries are most likely to be impacted by

sea level rise and as such should receive sustained attention. The creation of protected areas

(through a combination of public and private ownership) in as many of these regions as possible

should be a priority, with the goal of allowing increased inundation to lead to the formation of

new wetland habitats. Several areas in Grays Harbor already benefit from such arrangements;

much of the Johns River is protected as state land (WDFW), much of the area around the mouth

of the Humptulips River is owned by the Grays Harbor Audubon Society and WDFW, and a large

portion of South Bay is also protected by WDFW, the Washington Department of Natural

Resources, and Grays Harbor county.


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Climate Change in the Chehalis River and Grays Harbor Estuary · 2013. 4. 4. · (model A1FI,...

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