Effects of climate change on hydrology and water resources in the Blue Mountains, Oregon, USA

Abstract

In the semi-arid environment of the Blue Mountains, Oregon (USA), water is a critical resource for both ecosystems and human uses and will be affected by climate change in both the near- and long-term. Warmer temperatures will reduce snowpack and snow-dominated watersheds will transition to mixed rain and snow, while mixed rain and snow dominated watersheds will shift towards rain dominated. This will result in high flows occurring more commonly in late autumn and winter rather than spring, and lower low flows in summer, phenomena that may already be occurring in the Pacific Northwest. Higher peak flows are expected to increase the frequency and magnitude of flooding, which may increase erosion and scouring of the streambed and concurrent risks to roads, culverts, and bridges. Mapping of projected peak flow changes near roads gives an opportunity to mitigate these potential risks. Diminished snowpack and low summer flows are expected to cause a reduction in water supply for aquatic ecosystems, agriculture, municipal consumption, and livestock grazing, although this effect will not be as prominent in areas with substantial amounts of groundwater. Advanced planning could help reduce conflict among water users. Responding pro-actively to climate risks by improving current management practices, like road design and water management as highlighted here, may be among the most efficient and effective methods for adaptation.

Full text

Contents lists available at ScienceDirect
Climate Services
journal homepage: www.elsevier.com/locate/cliser
Effects of climate change on hydrology and water resources in the Blue
Mountains, Oregon, USA
Caty F. Clifton
a
, Kate T. Day
b
, Charles H. Luce
c,⁎
, Gordon E. Grant
d
, Mohammad Safeeq
e
,
Jessica E. Halofsky
f
, Brian P. Staab
a
a
U.S. Forest Service, Pacific Northwest Region, Portland, OR, USA
b
U.S. Forest Service, Colville National Forest, Colville, WA, USA
c
U.S. Forest Service, Rocky Mountain Research Station, Boise, ID, USA
d
U.S. Forest Service, Pacific Northwest Research Station, Corvallis, OR, USA
e
Sierra Nevada Research Institute, University of California, Merced, CA, USA
f
University of Washington, School of Environmental and Forest Sciences, Seattle, WA, USA
ARTICLE INFO
Keywords:
Climate change
Runoff
Snow
Low flows
Peak flows
Forest roads
Water supply
ABSTRACT
In the semi-arid environment of the Blue Mountains, Oregon (USA), water is a critical resource for both eco-
systems and human uses and will be affected by climate change in both the near- and long-term. Warmer
temperatures will reduce snowpack and snow-dominated watersheds will transition to mixed rain and snow,
while mixed rain and snow dominated watersheds will shift towards rain dominated. This will result in high
flows occurring more commonly in late autumn and winter rather than spring, and lower low flows in summer,
phenomena that may already be occurring in the Pacific Northwest. Higher peak flows are expected to increase
the frequency and magnitude of flooding, which may increase erosion and scouring of the streambed and
concurrent risks to roads, culverts, and bridges. Mapping of projected peak flow changes near roads gives an
opportunity to mitigate these potential risks. Diminished snowpack and low summer flows are expected to cause
a reduction in water supply for aquatic ecosystems, agriculture, municipal consumption, and livestock grazing,
although this effect will not be as prominent in areas with substantial amounts of groundwater. Advanced
planning could help reduce conflict among water users. Responding pro-actively to climate risks by improving
current management practices, like road design and water management as highlighted here, may be among the
most efficient and effective methods for adaptation.
Practical Implications
Water is a particularly valuable resource in the relatively dry
landscapes of the Blue Mountains region, Oregon (USA). Most
of that water is sourced from high-elevation public lands,
specifically the Malheur, Umatilla, and Wallowa-Whitman
National Forests. Snowpack, which is the key to downstream
water supply during the summer, may already be decreasing
in response to a warmer climate and will continue to decrease
in future decades. This will inevitably affect ecological pro-
cesses and human enterprises in the region.
A higher rain:snow ratio in the Blue Mountains is expected
to cause higher peak streamflows in late autumn and winter,
leading to increased frequency and magnitude of flooding
downstream. This will have the potential to damage roads,
especially in and near floodplains, and associated infra-
structure such as culverts and bridges. Refitting this infra-
structure for more severe conditions will create a financial
burden for the U.S. Forest Service, other public agencies, and
private landowners. Increase flooding may also reduce access
for recreational activities and resource management, possibly
for long periods of time. If damage is high enough, it will
require a prioritization of roads that can be maintained within
a sustainable transportation system, and perhaps the perma-
nent closure of some roads.
Reduced snowpack and earlier snowmelt will reduce hy-
drologic recharge of both surface and subsurface flows in
spring and summer. This will lead to lower streamflows in
summer in both rivers and smaller streams, creating adverse
conditions for coldwater fish species and other aquatic
https://doi.org/10.1016/j.cliser.2018.03.001
Received 27 January 2017; Received in revised form 22 October 2017; Accepted 6 March 2018
⁎
Corresponding author at: U.S. Forest Service, Rocky Mountain Research Station, 322 E Front St. Boise, ID 83702, USA (C.H. Luce).
E-mail address: cluce@fs.fed.us (C.H. Luce).
Climate Services xxx (xxxx) xxx–xxx
2405-8807/ © 2018 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Please cite this article as: Clifton, C.F., Climate Services (2018), https://doi.org/10.1016/j.cliser.2018.03.001

organisms. It will also reduce water supply for agriculture,
municipal uses (drinking water), industrial uses, livestock
grazing, and recreation. Reduced water supply will be an
especially important issue when multiple consecutive drought
years decrease water available for both aquatic ecosystems
and downstream human uses.
Currently, water allocation is mostly satisfactory in the
Blue Mountains region, and conflicts are occasional and lo-
calized. However, competition among different users may
become acute during future drought periods, and if low water
supply becomes a chronic situation, social and political solu-
tions may be needed to resolve conflicts. Finding a balance in
the near term among water allocated for ecological functions,
local communities, and economic benefits will help forestall
those conflicts.
1. Introduction
Water is a critical resource in arid and semi-arid forest and range-
land environments of western North America, typically limiting the
distribution of plant and animal species. Water is also a critical element
for human activities, affecting where and how human communities and
local economies persist across the landscape (Hartter et al., 2018). The
Blue Mountains of northeast Oregon and southeast Washington, most of
which are located within federal land, are the primary water source for
human uses, which include agriculture, drinking water, industrial uses,
livestock grazing, and recreation.
Climate change is expected to alter hydrologic processes in the
Pacific Northwest region of North America, thereby affecting key re-
sources and processes including water supply, infrastructure, aquatic
habitat, and access. A warmer climate will affect the amount, timing,
and type of precipitation, and the timing and rate of snowmelt (Luce
et al., 2012, 2013; Safeeq et al., 2013), which will in turn affect
snowpack volume (Hamlet et al., 2005; Luce et al., 2014a), streamflow
(Hidalgo et al., 2009; Elsner et al., 2010; Hamlet et al., 2013), and
stream temperature (Isaak et al., 2012; Luce et al., 2014b; Mantua et al.
2010). Altered precipitation patterns would also affect vegetation
(Kerns et al., 2018), which would in turn affect water supply (Adams
et al., 2012, Vose et al., 2016).
Federal lands dominate the headwaters of the major basins in the
Blue Mountains Ecoregion (Fig. 1). Understanding how climate change
will affect hydrologic processes will help federal land managers and
their many partners identify planning and management strategies that
maintain ecosystem function, water supply, and a sustainable road
system (Peterson and Halofsky, 2018). Reduced or less reliable water
supply affects local economic activities, planning, and resource man-
agement. Anticipatory planning can reduce conflicts and improve eco-
nomic and ecological outcomes during droughts. Damage to roads,
bridges, and culverts creates safety hazards, affects aquatic resources,
and incurs high repair costs. Reduced access to public lands reduces the
ability of land managers to preserve, protect, and restore resources and
to provide for public use of resources. Designing a less vulnerable road
network would again protect both ecological and economic interests.
Here we describe hydrologic processes in the Blue Mountains of
Oregon, historical trends in hydrologic parameters (snowpack, peak
streamflow, low streamflow, and stream temperatures), and projected
effects of climate change on these hydrologic parameters. We also
identify and map key sensitivities of water supply, roads, and infra-
structure to changes in climate and hydrology.
2. Effects of climate change on hydrologic processes
2.1. Methods
Hydrologic simulations of streamflow were prepared using the
Variable Infiltration Capacity (VIC) model (Liang et al., 1994) to si-
mulate streamflow driven by downscaled forcing data from global cir-
culation models (GCMs) that have contributed to the Intergovernmental
Panel on Climate Change AR4 (CMIP3) assessment (Elsner et al., 2010;
IPCC, 2007). VIC projections were prepared from an ensemble of 10
GCM models using A1B emission scenarios and having the best match
with observations in the historical period (Littell et al., 2011). Projec-
tions for the “2040s”cover an average from 2030 to 2059, and the
“2080s”cover 2070 to 2099. Historical metrics were based on the
period 1977 through 1997 (Wenger et al., 2010). VIC data were com-
puted on a 1/16th-degree (∼6 km) grid to produce daily flow data that
were further routed downstream and analyzed for metrics important to
aquatic ecology (Wenger et al., 2010, 2011). VIC outputs were further
processed with a linear groundwater reservoir routing algorithm using
the calibrated recession coefficient values of Safeeq et al. (2014) to
estimate impacts to low flows, which are sensitive to groundwater dy-
namics.
To assess changes in snowpack, we used the model of Luce et al.
(2014a), who evaluated snow sensitivity to climate at Snowpack Tele-
metry (SNOTEL) sites in the Pacific Northwest, developing projections
for April 1 snow water equivalent (SWE) for a scenario of 3 °C warmer
than the last 20 years. Validation of the model shows that it is suitable
to assess climate change effects (Lute and Luce, 2017).
Stream temperature changes were projected using the The NorWeST
Regional Stream Temperature Database (http://www.fs.fed.us/rm/
boise/AWAE/projects/NorWeST.html). NorWeST uses extensive stream
temperature observations and spatial statistical models to characterize
and project stream temperatures in the Blue Mountains (Isaak et al.,
2015, Isaak et al., this issue). Future stream temperatures were pro-
jected based on historical conditions, model projections of future cli-
mate, and assessments of past sensitivity to climate.
2.2. Effects of climate change on snowpack
The role of snow in watershed runoffin the Pacific Northwest is
determined to a great extent by mid-winter temperatures (Hamlet and
Lettenmaier, 2007). Rain-dominated basins are above freezing most of
the time in winter, and snow accumulation is minimal (< 10% of Oc-
tober-March precipitation). These basins typically have peak stream-
flows in winter, coinciding with peak precipitation, but may have
multiple peaks associated with individual rain events. Mixed rain and
snow (or transitional) basins collect substantial snowpack (10–40% of
October-March precipitation), and are typically slightly below freezing
in mid-winter. These basins have multiple seasonal streamflow peaks.
Snow-dominated basins are cold in winter, capturing > 40% of Oc-
tober-March precipitation as snow and have low flows through winter,
often with streamflow peaks in spring. The Blue Mountain region has all
three types of basins.
Over the last 50 years, increasing temperatures in the Pacific
Northwest have caused earlier snowmelt (Stewart et al., 2005; Hamlet
et al., 2007), and lower spring snowpack (Mote, 2003; Hamlet et al.,
2005; Mote et al., 2005). Snowpack is expected to be particularly
sensitive to future temperature increases, facilitating a change from
snowmelt-dominant to transitional basins, and from transitional to rain-
dominant basins (Tohver et al., 2014).
Decreases in snowpack persistence and April 1 SWE will be wide-
spread in the Blue Mountains, with the largest decreases in low to mid-
elevation locations. Large areas of the ecoregion are likely to lose sig-
nificant portions of April 1 SWE by the 2080s (Fig. 2). Snowpack sen-
sitivity will be relatively high even in some of the locally higher ele-
vation ranges such as the Strawberry Mountains, Monument Rock
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Wilderness, Wenaha-Tucannon Wilderness, and at mid-elevations in the
North Fork John Day, and Hells Canyon Wilderness. Much of the Eagle
Cap Wilderness, in the Wallowa Mountains, has the lowest sensitivity in
the area with declines in April 1 SWE on the order of 25% by the 2080s.
2.3. Effects of climate change on peak flows
Flooding in mountain watersheds in the Pacific Northwest is sensi-
tive to precipitation intensity, temperature (as it affects rain vs. snow),
and the combined effects of temperature and precipitation on snow
dynamics (Hamlet and Lettenmaier, 2007; Tohver et al., 2014). Floods
occur during autumn and winter (associated with heavy rainfall and
snowmelt) or in spring, associated with heavy snowpack and rapid
snowmelt (Hamlet and Lettenmaier, 2007; Sumioka et al., 1998).
Summer storms can also cause local flooding and mass wasting events
(such as landslides, gullies, and debris flows), particularly after wildfire
(Moody and Martin, 2009; Cannon et al., 2010; Luce et al., 2012).
Flooding can be exacerbated by rain-on-snow (ROS) events (Harr,
1986; Marks et al., 1998; McCabe et al., 2007; Eiriksson et al., 2013),
and a warmer climate is expected to alter ROS flood risk depending on
local conditions in different basins including elevation ranges and
groundwater dynamics (e.g. Safeeq et al., 2015). In general, the ROS
zone is expected shift upwards in elevation, which will tend to increase
flooding in basins where much of the basin is just above the elevation
where ROS is common. In contrast, in basins in which the ROS zone is
already high in the basin, the upward shift in the ROS zone may reduce
flooding.
Higher temperatures in the latter half of the 20th century have
caused earlier runoffin snowmelt-dominated and transitional water-
sheds in the western United States (Cayan et al., 2001; Stewart et al.,
2005; Hamlet et al., 2007). If temperature continues to increase, pos-
sibly accentuated by increased precipitation intensity, extreme
hydrologic events may become more frequent (Hamlet et al., 2013).
In the Blue Mountains, the hydrologic simulations estimate that
flood magnitude will increase in the Wallowa Mountains, Hells Canyon
Wilderness Area, and northeast Wallowa-Whitman National Forest by
the 2080s, particularly in mid-elevation areas (Fig. 3). High flow events
during winter are projected to change substantially in some areas, and
areas with the largest change in flood magnitude (Fig. 3) also have
altered frequency of those high flows occurring during winter months
(Fig. 4), which may be damaging for fish eggs in redds (Tonina et al.,
2008; Wenger et al., 2011; Goode et al., 2013; Isaak et al., this issue).
Some of the largest peak flow changes are occurring in areas where the
largest precipitation events (usually in November and December) now
commonly fall as snow and are expected more frequently to come as
rain falling on snow in the future. It is this shift in mechanism that
contributes most strongly to flood magnitude increases. Other areas in
the ecoregion already experience substantial rain-on-snow.
2.4. Effects of climate change on low flows
Earlier snowmelt over the last 50 years has reduced spring, early
summer, and late summer flows in the western United States (Leppi
et al., 2011; Safeeq et al., 2013; Kormos et al., 2016). The 25th per-
centile flows (drought year flows, 1948–2006) have become even lower
across the Pacific Northwest (Luce and Holden, 2009), and large de-
creasing fractional flows have been documented for eastern Oregon in
March-June (Stewart et al., 2005). Summer low flows are affected by
both snowmelt and landscape drainage efficiency (Tague and Grant,
2009; Safeeq et al., 2013). In the Blue Mountains, which have a mod-
erate groundwater component, summer flows decreased 21–28% be-
tween 1949 and 2010 (Safeeq et al., 2013).
Within the Blue Mountain region, snow-dominated regions with late
snowmelt, such as the Wallowa Mountains, have high streamflow
Fig. 1. National Forests and major basins in the Blue Mountains Ecoregion.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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sensitivity to a change in the magnitude and timing of recharge at broad
spatial scales (Safeeq et al., 2014), especially in early summer. Other
parts of the Blue Mountains have low-moderate sensitivity to changes in
magnitude and timing of snowmelt, although sensitivity in the Wallowa
Mountains is higher in early summer. Projections of future low flows
using the hydrologic simulations indicate small decreases in summer
streamflow (< 10%) for about half of perennial streams in the Blue
Mountains by 2080 (Fig. 5), although some of the more sensitive areas
(Wallowa Mountains, Elkhorn Mountains, Wenaha-Tucannon Wild-
erness) show > 30% streamflow decreases by 2080. Note that many of
the most sensitive areas for low flows are areas that have lower sensi-
tivity for snowpack (Fig. 2) because these are areas where late-lying
snow has always been an important contributor to summer runoff, and
small changes in snowpack drive large changes in low flow (Safeeq
et al., 2014).
2.5. Effects of climate change on water quality
Historical temperatures in unregulated streams across the Pacific
Northwest paralleled air temperature trends at nearby weather stations
from 1980 to 2009 (Isaak et al., 2010, 2012), and stream temperatures
increased significantly in summer, autumn, and winter, with the highest
rates of warming in summer (reconstructed trend of 0.22 °C per
decade). A significant stream cooling trend occurred during spring,
associated with a regional trend of cooler air temperature (Isaak et al.,
2012; Abatzoglou et al., 2014). Most of the variation in long-term
stream temperature (80–90%) was explained by air temperature trends
and a smaller proportion by discharge (10–20%). A separate study of
stream data found variable trends in stream temperature, with
increased temperature at some sites in the Pacific Northwest (28–44%)
and decreased temperature at others (22–33%) (Arismendi et al., 2012).
Discrepancies are attributed to differences in length of record and lo-
cation relative to dams, with warming more apparent in the longer
datasets. Cold streams were generally not as sensitive as warm streams
to varying climatic conditions (Luce et al., 2014b; Isaak et al., 2016).
Therefore, the relatively warm streams in the Blue Mountains are ex-
pected to be quite sensitive to a warmer climate.
Decreasing summer moisture and warming temperatures in dry
forests of the western United States may contribute to forest mortality
in some locations (e.g., Meddens and Hicke, 2014; Allen et al., 2015;
McDowell et al., 2015; Luce et al., 2016) and increased wildfire area
burned (Littell et al., 2009; Littell et al., 2016). Increased wildfire,
particularly if it occurs in riparian areas, would contribute to stream
temperature increases (Dunham et al., 2007; Isaak et al. 2010). These
risks are not characterized in the projections in this region, but illus-
trate that care in riparian management and land management that re-
duces wildfire spread can ameliorate projected warming.
Projections estimate that basin-wide average August stream tem-
peratures in the Blue Mountains will increase 1 °C by 2040 and nearly
2 °C by 2080 in response to higher air temperature, with warmer
streams in the basin likely to warm faster than cooler ones.
3. Consequences of hydrologic changes for water management
In the dry climate of the Blue Mountains region, many different
parties lay claim to use of water resources to support habitation and
economic enterprises. About 6800 water rights claims are located on
National Forest lands: 43% for domestic livestock, 32% for instream
Fig. 2. Projected change in snow water equivalent from present to the 2080s in the Blue Mountains. Names indicate Wilderness areas and other high elevation ranges
in the region to provide some reference for topography. Projections were modeled based on the methods of Luce et al. (2014a) using downscaled weather from
Abatzoglou and Brown (2012).
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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flows, 9% for wildlife, 5% for irrigation, and 3% for domestic use (320
points of diversion) (Gecy, 2014). Instream flows account for 75% of
water rights by volume. Six larger towns rely directly on the national
forests for water supply, and 20 small communities rely on surface
water or groundwater from the Blue Mountains for drinking water.
Water is critical for livestock in national forests and surrounding lands,
with grazing occurring in 80% of sub-watersheds in the Blue Moun-
tains.
Water in national forest basins is fully allocated in summer, and
although it is typically available for campgrounds, administrative sites,
and other uses (e.g., livestock and wildlife), water may be limited in dry
years. Dams and stream diversions affect local hydrology and in some
cases ecological functions (Dwire et al., 2018). It is uncertain how long-
term warming or short-term droughts will affect permitted water use,
although significant changes in water use on the National Forests
during the next decade are unlikely.
As discussed above, warming temperatures will lead to decreased
snowpack and earlier snowmelt, altering streamflow patterns and de-
creasing water availability in summer. Most precipitation in the Blue
Mountains falls during winter when consumptive demand is low. Rain
is infrequent, and streams depend on groundwater to maintain flows in
summer. Because water supply in summer is limited, climate change
may make it difficult to meet current demands during extreme drought
years and following consecutive drought years, especially after the mid
21st century. Current conflict over water use in the Blue Mountains
region is not a prominent issue, although future water shortages caused
by declines in dry season flows may create social and political tension if
different sectors (e.g., agriculture and municipal) compete for water.
Declining summer flows caused by reduced snowpack accumulation
and earlier snowmelt in the Blue Mountains could affect water avail-
ability during peak summer demand. Diversions from streams draining
high elevation areas may show the greatest changes (Fig. 6) even
though the snowpacks there are the most resilient. Summer flows are so
dependent on snow inputs in mid-summer that the declines in snow-
pack will be felt most strongly there. In contrast, basins with little snow
in summer already are less likely to be affected by large snowpack
declines. The Burnt, Powder, Upper Grande Ronde, Silver, Silvies,
Upper John Day, Wallowa, and Willow sub-basins (Fig. 1) are at highest
risk for summer water shortage associated with low streamflow.
Widespread diversions increase water extraction across the landscape,
with aging (leaky) infrastructure contributing to water loss.
Water availability is an important attribute of the Watershed
Condition Framework (WCF) classification system used to rate wa-
tershed condition in national forests (Potyondy and Geier, 2011). Most
sub-watersheds in the Blue Mountains are rated as “functioning”or
“functioning at risk,”based on flow alterations from diversions, with-
drawals, and dams relative to natural flows and groundwater storage.
The Burnt, Powder, Upper Grande Ronde, and Wallowa sub-basins have
the most sub-watersheds with “impaired function”for water quantity.
The highest off-forest consumptive uses are in the Burnt, Malheur,
Powder, Silver Creek, Silvies, Umatilla, and Walla Walla basis (Gecy,
2014), most of which are expected to have moderate to high changes in
summer flows (Fig. 6).
4. Consequences of hydrologic changes for roads, infrastructure,
and access
Roads, trails, bridges, and other infrastructure in the Blue
Mountains have historically provided access for land managers, mineral
prospectors, loggers, hunters, and recreationists. The U.S. Forest Service
is mandated to provide multiple resources across this landscape, and
access to water resources, timber and range resources, wildlife, and
enjoyment by the public has largely determined where these activities
occur. Sustainable management of access promotes use, stewardship,
Fig. 3. Projected change in the 1.5-year flood magnitude between the historical period (1970–1999) and the 2080s for the Blue Mountains region.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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and appreciation of public lands for their social and economic values
(Louter, 2006).
The three national forests assessed here, the Malheur, Umatilla, and
Wallow-Whitman National Forests, contain 37,500 km of roads: 800 km
paved, 17,800 km gravel, and 18,900 km native-surface (Table 1). Road
density is highest at low elevations and near mountain passes. Roads
and trails cross many streams, with 96% of crossings being culverts
installed decades ago. Some crossings are being replaced, but many
have not been inventoried and conditions are unknown. Older roads are
more likely to be near streams, thus increasing risks for damage to roads
and aquatic resources.
Although the need for roads for timber harvest has decreased
greatly in the past 20 years, demand for roads for recreational activities
has increased. Hiking and camping are the most popular warm-weather
activities, with greater than 60% of trips to national forests lasting 6 h
or less (USFS, 2010), thus concentrating human impacts on areas that
are easily accessible. Demand is increasing for trail use by mountain
bikes, off-highway vehicles, and winter recreation.
4.1. Road management
The condition of roads and trails in the Blue Mountains is a function
of their age, design, maintenance practices, and location. Culverts were
typically designed to withstand a 25-year flood. Road construction has
declined since the 1990s, with few new roads being added. Roads ac-
celerate runoffrates and decrease late-season flows, increase peak
flows, and increase erosion rates (e.g. Wigmosta and Perkins, 2001;
Lamarche and Lettenmaier, 2001; Bowling, 2001; Wemple and Jones,
2003). Impacts are greater for roads near streams, although roads in
uplands also affect surface and subsurface flows and erosion (Luce,
2002; Trombulak and Frissell, 2000).
National forest engineering staffare charged with operating a sus-
tainable transportation system that is safe, responsive to public needs,
and causes minimal environmental impact. Potential management ac-
tions include reducing road maintenance levels (e.g. Luce and Black,
2001), storm-proofing roads, upgrading drainage structures and stream
crossings, reconstructing and upgrading roads, decommissioning roads,
and converting roads to alternative modes of transportation. Activities
that are critical to health and safety receive priority in decisions about
which roads to repair and maintain, balanced with consideration for
access and aquatic habitat (Luce et al., 2001; Trombulak and Frissell,
2000).
The Malheur, Umatilla, and Wallow-Whitman National Forests are
currently identifying a sustainable road network that is ecologically and
fiscally sustainable in accordance with the 2001 Road Management
Rule (36 CFR 212, 261, 295). Their transportation analysis assesses the
condition of existing roads, including options for removing damaged or
unnecessary roads, and maintaining and improving necessary roads.
This process increases the agency’s ability to acquire funding for road
improvement and decommissioning, provides a framework for annual
maintenance costs, facilitates agreement with regulatory agencies, and
increases financial sustainability.
Reconstruction and decommissioning of roads and trails require an
environmental assessment and public involvement. The Water and
Fig. 4. The average number of winter days each year that are in the top 5% (18 days) for that year based on flow. This addresses whether high flow events typically
occur in winter (December-March), when fall spawning fish have eggs in the gravel, or in other months. Values are displayed the historical period (1970–1999) (left)
and projected for 2080 (right).
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Erosion Predictive model (Flanagan and Nearing, 1995), Geomorphic
Road Analysis and Inventory Package (GRAIP) (Black et al., 2012;
Cissel et al., 2012), and NetMap (Benda et al., 2007) are often used to
identify hydrologic impacts and guide management on projects. For
example, the Wall Creek watershed GRAIP analysis in the Umatilla
National Forest determined that 12% of the road system contributed
90% of the sediment, providing the information needed to prioritize
critical sites (Nelson et al., 2010).
4.2. Climate change effects on transportation systems
Climate and hydrology will influence the transportation system in
the Blue Mountains through reduced snowpack, resulting in a longer
season of road use, higher peak flows and flood risk (Fig. 7), and in-
creased landslide risk (Strauch et al., 2014). Increased wildfire dis-
turbance (Kerns et al., 2018) plus higher peak flows may contribute to
increased erosion and landslides (Goode et al., 2012). Direct (physical)
effects of climate change occur from floods, snow, landslides, extreme
temperatures, and wind, whereas indirect effects include secondary
influences on access related to public safety and visitor use patterns.
Effects on roads will be related to weather events (e.g., a single storm),
but the risks of such events are a characteristic of the climate. An in-
crease in the size of rare events will have major effects on hydrologic
systems and may require changes of current design standards for in-
frastructure.
In the highly dissected northern Blue Mountains, more intense
winter storms and more rain-on-snow events (Salathé et al., 2014) may
cause shallow debris slides to become more frequent, potentially da-
maging infrastructure and reducing access. In addition, reduced
snowpack is expected to increase antecedent soil moisture in winter
(Hamlet et al., 2013).
Vulnerability of roads to erosion and mass wasting (e.g. landslides
and gullies) processes varies depending on topography, geology, slope
stability, age, design, location, and use (Luce and Wemple, 2001;
Wemple et al., 2001). Roads and trails built decades ago have often
deteriorated, and many infrastructure components are near the end of
their design lifespan. Culverts were typically designed to last
25–75 years, and if they are beyond their design life, rust and wear
make them less resilient to high flows and bed load movement and
more susceptible to structural and piping failure. Even storms of low to
moderate intensity can damage roads and trails that are already com-
promised. Roads and trails built on steep slopes are particularly vul-
nerable to erosion and mass failures. The road network built to facilitate
past timber harvesting has contributed to the sensitivity of roads and
other infrastructure by increasing storm runoffand peak flows (Schmidt
et al., 2001; Croke and Hairsine, 2006). Roads and trails in valley
bottoms are built on gentle grades, but proximity to streams increases
sensitivity to flooding, channel migration, and bank erosion. Most road-
stream crossings use culverts rather than bridges, and culverts are more
sensitive to high streamflows and debris movement. Highways in the
Blue Mountains, with higher design and maintenance standards, will be
less vulnerable to climate change than unpaved roads in national for-
ests. Currently, budgets are often insufficient to maintain and repair
infrastructure, thus increasing the susceptibility of the transportation
system.
New or replaced infrastructure could increase resilience to climate
change because materials and standards have improved in recent years.
For example, new culverts and bridges are often wider than the original
structures, and open-bottomed, arched culverts are now often used in
the Blue Mountains to improve fish passage and stream function.
Fig. 5. Projected change in mean summer streamflow from the historic time period (1970–1999) to the 2080s for streams in the Blue Mountains region. Projections
created by modifying standard VIC projections (following Wenger et al., 2010) routed through a linear groundwater reservoir model, using calibrated recession
parameters for each watershed from Safeeq et al. (2014).
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
7

Natural channel design, which mimics upstream and downstream
conditions, is often used at stream crossings, and helps pass larger
pieces of wood.
4.3. Short-term climate change effects on other infrastructure and access
In the short-term changes in runoffand geomorphology will directly
challenge the road network integrity. Higher peak flows in winter in-
crease the potential impacts of flooding roads, trails, campgrounds, and
structures (Walker et al., 2011; MacArthur et al., 2012). Increased risk
of landslides in some areas will contribute to flooding by diverting
water, blocking drainage, and filling channels with debris (Crozier,
1986; Chatwin et al., 1994; Schuster and Highland, 2003).
In addition, altered hydrologic regimes in the Blue Mountains may
contribute to safety hazards. Damaged roads reduce access for re-
sponding to emergencies, and higher streamflows could create
hazardous conditions for river recreation and campers. More wildfires
(Kerns et al., 2018) would further restrict emergency access by in-
creasing downed logs and road damage, reducing agency capacity to
respond to additional fires and to emergency needs in local commu-
nities (Strauch et al., 2014).
4.4. Medium and long-term effects on access
As change progresses, runoffand geomorphic impacts could become
more severe and widespread, and accumulated minor impacts will ex-
acerbate the outcomes. More frequent flooding will continue to increase
sediment and debris transport, damaging stream-crossing structures.
Shifting channel dynamics caused by increased flow and sediment may
compound problems, even if crossing structures are upgraded to ac-
commodate higher flows. Repeated landslides can cause aggradation in
streams, thus elevating future flood potential, and culverts blocked with
debris can cause flooding and associated damage to roads, trails, and
campgrounds (Halofsky et al., 2011).
In the long term, higher winter soil moisture may increase the risk
of landslides in autumn and winter, especially in areas that have ex-
perienced high-severity wildfire and insect outbreaks (Montgomery
et al., 2000; Schmidt et al., 2001; Istanbulluoglu et al., 2004). Although
floods and landslides will continue to be more common in areas with
known susceptibility (e.g., high density roads, steep slopes), they may
also occur in higher elevation locations currently covered by snowpack
for much of the year (MacArthur et al., 2012).
A longer snow-free season will extend visitor use in spring and au-
tumn, especially at higher elevations (Rice et al., 2012). Trailheads at
lower elevations may be accessible earlier, but hazards associated with
snow bridges and avalanche chutes may persist along trails. River raf-
ters may encounter unfavorable conditions from lower streamflows in
Fig. 6. Projected risk of summer water shortage in the Blue Mountains region, based on low streamflows for 2080s. The data in Fig. 5 were used to calculate
differences averaged over each watershed.
Table 1
Kilometers of road by maintenance level in national forests in the Blue
Mountains.
Operational maintenance levels National forests
Malheur Umatilla Wallowa-Whitman
Kilometers
Basic custodial care (closed) 6059 3543 7216
High-clearance cars/trucks 8814 3131 6719
Suitable for passenger cars 587 545 435
Passenger car (moderate comfort) 0 114 29
Passenger car (high comfort) 0 132 210
All roads 15,460 7465 14,609
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
8

late summer (Mickelson, 2009), as well as hazards associated with
deposited sediment and woody debris from high winter flows. Warmer
winters may shift river recreation to times of the year when risks of
extreme weather and flooding are higher.
Some benefits to access and transportation in the Blue Mountains
may accrue from the effects of climate change. Lower snow cover will
reduce the cost of snow removal from roads, and allow earlier access for
snow removal and maintenance in low-mid elevation areas and a longer
construction season at higher elevations (e.g., installation of temporary
trail bridges). As noted above, less snow may increase access for warm-
weather recreation, but may reduce opportunities for winter recreation
(Joyce et al., 2001; Morris and Walls, 2009). The highest elevations of
the Blue Mountains are expected to retain a significant amount of snow,
at least for the next few decades, which may focus snow-based activities
in fewer areas as snow at lower elevations decreases.
Acknowledgments
We thank Robert Gecy, David Salo, and Thomas Friedrichsen for
helpful discussions and contributions. Assistance with redrafting
Figures was provided by Wes Hoyer and Amy Mathie. We also thank
participants in the hydrology group at the Blue Mountains Adaptation
Partnership workshop in La Grande, Oregon, for their valuable con-
tributions to this chapter. The manuscript has benefitted from the ad-
vice of two anonymous reviewers.
References
Abatzoglou, J.T., Brown, T.J., 2012. A comparison of statistical downscaling methods
suited for wildfire applications. Int. J. Climatol. 32 (5), 772–780.
Abatzoglou, J.T., Rupp, D.E., Mote, P.W., 2014. Seasonal climate variability and change
in the Pacific Northwest of the United States. J. Clim. 27, 2125–2142.
Adams, H.D., Luce, C.H., Breshears, D.D., et al., 2012. Ecohydrological consequences of
drought- and infestation-triggered tree die-off: insights and hypotheses.
Ecohydrology 5, 145–159.
Allen, C.D., Breshears, D.D., McDowell, N.G., 2015. On underestimation of global vul-
nerability to tree mortality and forest die-offfrom hotter drought in the
Anthropocene. Ecosphere 6 art129.
Arismendi, I., Johnson, S.L., Dunham, J.B., et al., 2012. The paradox of cooling streams in
a warming world: regional climate trends do not parallel variable local trends in
stream temperature in the Pacific continental United States. Geophys. Res. Lett. 39,
L10401.
Benda, L., Miller, D., Andras, K., et al., 2007. NetMap: a new tool in support of watershed
science and resource management. For. Sci. 53, 206–219.
Black, T.A., Cissel, R.M., Luce, C.H., 2012. The geomorphic road analysis and inventory
package (GRAIP). Volume 1: data collection method. Gen. Tech. Rep. RMRS-GTR-
280WWW. U.S. Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
Bowling, L.C., Lettenmaier, D.P., 2001. The effects of forest roads and harvest on
catchment hydrology in a mountainous maritime environment. In: Land Use and
Watersheds: Human Influence on Hydrology and Geomorphology in Urban and Forest
Areas, M.S. Wigmosta and S.J. Burges, eds., AGU Water Science and Application
Volume 2, pp. 145–164.
Cannon, S.H., Gartner, J.E., Rupert, M.G., et al., 2010. Predicting the probability and
volume of postwildfire debris flows in the intermountain western United States. Geol.
Soc. Amer. Bull. 122, 127–144.
Cayan, D.R., Dettinger, M.D., Kammerdiener, S.A., et al., 2001. Changes in the onset of
spring in the western United States. Bull. Am. Met. Soc. 82, 399–415.
Chatwin, S.C., Howes, D.E., Schwab, J.W., Swantson, D.N. 1994. A guide for management
of landslide-prone terrain in the Pacific Northwest. Land Manage. Handb. 18. 2nd ed.
British Columbia Ministry of Forests, Research Program, Victoria, British Columbia.
Cissel, R.M., Black, T.A., Schreuders, K.A.T., et al., 2012. The geomorphic road analysis
and inventory package (GRAIP). Volume 2: office procedures. Gen. Tech. Rep. RMRS-
GTR-281WWW. U.S. Forest Service, Rocky Mountain Research Station, Fort
Collins, CO.
Croke, J., Hairsine, P., 2006. Sediment delivery in managed forest: a review. Environ.
Rev. 14, 59–87.
Crozier, M.J., 1986. Landslides: Causes, Consequences, and Environment. Croom Helm
Ltd., Dover, NH.
Dunham, J.B., Rosenberger, A.E., Luce, C.H., Rieman, B.E., 2007. Influences of wildfire
and channel reorganization on spatial and temporal variation in stream temperature
and the distribution of fish and amphibians. Ecosystems 10, 335–346.
Fig. 7. Projected change in bankfull flow for roads within 90 m of a stream for the 2080s. The Variable Infiltration Capacity model was used to calculate differences in
Q1.5-bankfull flow between historic data (1915–2006) and the 2080s. Not all vulnerable roads are represented; some roads intersect smaller intermittent streams.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
9

Dwire, K.A., Mellmann-Brown, S., Gurrieri, J.T., 2018. Potential effects of climate change
on riparian areas, wetlands, and groundwater-dependent ecosystems in the Blue
Mountains, Oregon, USA. Clim. Serv. http://dx.doi.org/10.1016/j.cliser.2017.10.
002.
Eiriksson, D., Whitson, M., Luce, C.H., et al., 2013. An evaluation of the hydrologic re-
levance of lateral flow in snow at hillslope and catchment scales. Hydrol. Process. 27,
640–654.
Elsner, M.M., Cuo, L., Voisin, N., Deems, J.S., Hamlet, A.F., Vano, J.A., Lettenmaier, D.P.,
2010. Implications of 21st century climate change for the hydrology of Washington
State. Clim. Change 102 (1), 225–260.
Flanagan, D.C., Nearing, M.A. (Eds.), 1995. USDA–Water erosion prediction project
hillslope profile and watershed model documentation. Nat. Soil Erosion Res. Lab.
Rep. 10. West U.S. Department of Agriculture, National Soil Erosion Research
Laboratory, Lafayette, IN.
Gecy, R., 2014. Blue Mountain forest plan revision draft environmental impact statement.
Watershed function, water quality, and water uses section. http://www.fs.usda.gov/
detail/wallowa-whitman/landmanagement/planning/?cid=stelprd3792957 (ac-
cessed 16.06.18).
Goode, J.R., Buffington, J.M., Tonina, D., et al., 2013. Potential effects of climate change
on streambed scour and risks to salmonid survival in snow-dominated mountain
basins. Hydrol. Process. 27, 750–765.
Goode, J.R., Luce, C.H., Buffington, J.M., 2012. Enhanced sediment delivery in a chan-
ging climate in semi-arid mountain basins: implications for water resource manage-
ment and aquatic habitat in the northern Rocky Mountains. Geomorphology
139–140, 1–15.
Halofsky, J.E., Shelmerdine, W.S., Stoddard, R., et al., 2011. Climate change, hydrology,
and road management at Olympic National Forest and Olympic National Park. In:
Halofsky, J.E., Peterson, D.L., O’Halloran, K.A., Hoffman, C.H. (Eds.), Adapting to
climate change at Olympic National Forest and Olympic National Park. Gen. Tech.
Rep. PNW-GTR-844. U.S. Forest Service, Pacific Northwest Research Station,
Portland, OR, pp. 21–42.
Hamlet, A.F., Elsner, M.M., Mauger, G.S., et al., 2013. An overview of the Columbia Basin
climate change scenarios project: approach, methods, and summary of key results.
Atmos.-Ocean 51, 392–415.
Hamlet, A.F., Lettenmaier, D.P., 2007. Effects of 20th century warming and climate
variability on flood risk in the western US. Water Resour. Res. 43, W06427.
Hamlet, A.F., Mote, P.W., Clark, M.P., Lettenmaier, D.P., 2005. Effects of temperature and
precipitation variability on snowpack trends in the western U.S. J. Clim. 18,
4545–4561.
Hamlet, A.F., Mote, P.W., Clark, M.P., Lettenmaier, D.P., 2007. 20th century trends in
runoff, evapotranspiration, and soil moisture in the Western U.S. J. Clim. 20,
1468–1486.
Hartter, J., Hamilton, L.C., Boag, A.E., Stevens, F.R., Ducey, M.J., Christoffersen, N.D.,
Oester, P.T., Palace, M.W., 2018. Does it matter if people think climate change is
human caused? Clim. Serv. http://dx.doi.org/10.1016/j.cliser.2017.06.014.
Harr, R.D., 1986. Effects of clearcutting on rain-on-snow runoffin western Oregon: a new
look at old studies. Water Resour. Res. 22, 1095–1100.
Hidalgo, H.G., Das, T., Dettinger, M.D., et al., 2009. Detection and attribution of
streamflow timing changes to climate change in the western United States. J. Clim.
22, 3838–3855.
Intergovernmental Panel on Climate Change (IPCC), 2013. Summary for policymakers. In:
Stocker, T.F., Qin, D., Plattner, G.K., et al. (Eds.), Climate Change 2013: The Physical
Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the
Intergovernmental Panel on Climate Change. Cambridge University Press,
Cambridge, United Kingdom.
Isaak, D.J., Luce, C.H., Rieman, B.E., et al., 2010. Effects of climate change and wildfire
on stream temperatures and salmonid thermal habitat in a mountain river network.
Ecol. Applic. 20, 1350–1371.
Isaak, D.J., Wollrab, S., Horan, D., Chandler, G., 2012. Climate change effects on stream
and river temperatures across the northwest U.S. from 1980–2009 and implications
for salmonid fishes. Clim. Change 113, 499–524.
Isaak, D.J., Young, M.K., Nagel, D.E., et al., 2015. The cold-water climate shield: deli-
neating refugia for preserving salmonid fishes through the 21st century. Glob. Change
Biol. 21, 2540–2553.
Isaak, D.J., Young, M.K., Luce, C.H., et al., 2016. Slow climate velocities of mountain
streams portend their role as refugia for cold-water biodiversity. Proc. Nat. Acad. Sci.
U.S.A. 113, 4374–4379.
Istanbulluoglu, E., Tarboton, D.G., Pack, R.T., Luce, C.H., 2004. Modeling of the inter-
actions between forest vegetation, disturbances, and sediment yields. J. Geophys.
Res. 109, F01009.
Joyce, L., Abers, J., McNulty, S., et al., 2001. Potential consequences of climate variability
and change for the forests of the United States. In: Melillo, J., Janetos, A., Karl, T.
(Eds.), Climate Change Impacts on the United States: The Potential Consequences of
Climate Variability and Change. Cambridge University Press, Cambridge, United
Kingdom, pp. 489–524.
Kerns, B.K., Powell, D.C., Mellmann-Brown, S., Carnwath, G., Kim, J.B., 2018. Effects of
projected climate change on vegetation in the Blue Mountains ecoregion, USA. Clim.
Serv. http://dx.doi.org/10.1016/j.cliser.2017.07.002.
Kormos, P., Luce, C., Wenger, S.J., Berghuijs, W.R., 2016. Trends and sensitivities of low
streamflow extremes to discharge timing and magnitude in Pacific Northwest
mountain streams. Water Resour. Res. http://dx.doi.org/10.1002/2015WR018125.
Lamarche, J., Lettenmaier, D.P., 2001. Effects of forest roads on flood flows in the
Deschutes River Basin, Washington. Earth Surf. Process. Landforms 26, 115–134.
Leppi, J.C., DeLuca, T.H., Harrar, S.W., Running, S.W., 2011. Impacts of climate change
on August stream discharge in the Central-Rocky Mountains. Clim. Change 112,
997–1014.
Liang, X., Lettenmaier, D.P., Wood, E.F., Burges, S.J., 1994. A simple hydrologically based
model of land surface water and energy fluxes for General Circulation Models. J.
Geophys. Res. 99 (D7), 14415–14428.
Littell, J.S., Elsner, M.M., Mauger, G., et al., 2011. Regional climate and hydrologic
change in the northern U.S. Rockies and Pacific Northwest: internally consistent
projections of future climate for resource management. University of Washington,
Climate Impacts Group, Seattle, WA. http://cses.washington.edu/picea/USFS/pub/
Littell_etal_2010 (accessed 16.06.18).
Littell, J.S., McKenzie, D., Peterson, D.L., Westerling, A.L., 2009. Climate and wildfire
area burned in western U.S. ecoprovinces, 1916–2003. Ecol. Applic. 19, 1003–1021.
Littell, J.S., Peterson, D.L., Riley, K.L., et al., 2016. A review of the relationships between
drought and forest fire in the United States. Glob. Change Biol. 22, 2353–2369.
Louter, D., 2006. Windshield Wilderness: Cars, Roads, and Nature in Washington’s
National Parks. University of Washington Press, Seattle, WA.
Luce, C.H., 2002. Hydrological processes and pathways affected by forest roads: what do
we still need to learn? Hydrol. Process. 16, 2901–2904.
Luce, C.H., Abatzoglou, J.T., Holden, Z.A., 2013. The missing mountain water: slower
westerlies decrease orographic enhancement in the Pacific Northwest, USA. Science
342, 1360–1364.
Luce, C.H., Black, T.A., 2001. Effects of Traffic and Ditch Maintenance on Forest Road
Sediment Production Proceedings of the Seventh Federal Interagency Sedimentation
Conference (Vol. 2, pp. 67-74). Reno, NV: Subcommittee on Sedimentation.
Luce, C.H., Holden, Z.A., 2009. Declining annual streamflow distributions in the Pacific
Northwest United States, 1948–2006. Geophys. Res. Lett. 36, L16401.
Luce, C.H., Lopez-Burgos, V., Holden, Z., 2014a. Sensitivity of snowpack storage to pre-
cipitation and temperature using spatial and temporal analog models. Water Resour.
Res. 50, 9447–9462.
Luce, C., Morgan, P., Dwire, K., et al., 2012. Climate change, forests, fire, water, and fish:
building resilient landscapes, streams, and managers. Gen. Tech. Rep. RMRS-GTR-
290. U.S. Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
Luce, C.H., Rieman, B.E., Dunham, J.B., et al., 2001. Incorporating Aquatic Ecology into
Decisions on Prioritization of Road Decommissioning. Water Resour. Impact 3, 8–14.
Luce, C., Staab, B., Kramer, M., et al., 2014b. Sensitivity of summer stream temperatures
to climate variability in the Pacific Northwest. Water Resour. Res. 50, 3428–3443.
Luce, C.H., Vose, J.M., Pederson, N., Campbell, J., Millar, C., Kormos, P., Woods, R.,
2016. Contributing factors for drought in United States forest ecosystems under
projected future climates and their uncertainty. For. Ecol. Manage. 380, 299–308.
http://dx.doi.org/10.1016/j.foreco.2016.05.020.
Luce, C.H., Wemple, B.C., 2001. Introduction to special issue on hydrologic and geo-
morphic effects of forest. Earth Surf. Proc. Landf. 26, 111–113.
Lute, A.C., Luce, C.H., 2017. Are model transferability and complexity antithetical?
Insights from validation of a variable-complexity snow model in space and time.
Water Resour. Res. http://dx.doi.org/10.1002/2017WR020752. in press.
MacArthur, J., Mote, P., Ideker, J., et al., 2012. Climate change impact assessment for
surface transportation in the Pacific Northwest and Alaska. Res. Rep. WA-RD 772.1.
State of Washington, Department of Transportation, Office of Research and Library
Services, Olympia, WA. http://www.wsdot.wa.gov/research/reports/fullreports/
772.1.pdf. (accessed 16.06.18).
McDowell, N.G., Williams, A.P., Xu, C., et al., 2015. Multi-scale predictions of massive
conifer mortality due to chronic temperature rise. Nat. Clim. Change 6, 295–300.
Mantua, N., Tohver, I., Hamlet, A., 2010. Climate change impacts on streamflow extremes
and summertime stream temperature and their possible consequences for freshwater
salmon habitat in Washington State. Clim. Change 102, 187–223.
Marks, D., Kimball, J., Tingey, D., Link, T., 1998. The sensitivity of snowmelt processes to
climate conditions and forest cover during rain-on-snow: a case study of the 1996
Pacific Northwest flood. Hydrol. Process. 12, 1569–1587.
McCabe, G.J., Clark, M.P., Hay, L.E., 2007. Rain-on-snow events in the western United
States. Bull. Am. Meteorol. Soc. 88, 319–328.
Meddens, A.J., Hicke, J.A., 2014. Spatial and temporal patterns of Landsat-based detec-
tion of tree mortality caused by a mountain pine beetle outbreak in Colorado, USA.
For. Ecol. Manage. 322, 78–88.
Mickelson, K.E.B., 2009. Impacts of regional climate change on the Pacific Northwest
white water recreation industry. Master’s thesis, University of Washington,
Seattle, WA.
Montgomery, D.R., Schmidt, K.M., Greenberg, H.M., Dietrich, W.E., 2000. Forest clearing
and regional landsliding. Geology 28, 311–314.
Moody, J.A., Martin, D.A., 2009. Synthesis of sediment yields after wildland fire in dif-
ferent rainfall regimes in the western United States. Int. J. Wildl. Fire 18, 96–115.
Morris, D., Walls, M., 2009. Climate change and outdoor recreation resources for the
future: background. Resources for the Future, Washington, DC. http://www.rff.org/
RFF/Documents/RFF-BCK-ORRG_ClimateChange.pdf. (accessed 16.06.18).
Mote, P.W., 2003. Trends in snow water equivalent in the Pacific Northwest and their
climatic causes. Geophys. Res. Lett. 30, 1601.
Mote, P.W., Hamlet, A.F., Clark, M., Lettenmaier, D.P., 2005. Declining mountain
snowpack in western North America. Bull. Am. Meteorol. Soc. 86, 39–49.
Nelson, N., Clifton, C., Black, T., et al., 2010. Wall Creek watershed GRAIP roads as-
sessment, North Fork John Day subbasin, Umatilla National Forest. U.S. Forest
Service, Rocky Mountain Research Station, Boise, ID. http://www.fs.fed.us/GRAIP/
downloads/case_studies/WallCreekWatershed2010.pdf. (accessed 16.06.18).
Peterson, D.L., Halofsky, J.E., 2018. Adapting to the effects of climate change on natural
resources in the Blue Mountains, USA. Clim. Serv. http://dx.doi.org/10.1016/j.cliser.
2017.06.005.
Potyondy, J.P., Geier, T.W., 2011. Watershed condition classification technical guide. FS-
978. U.S. Forest Service, Washington, DC.
Rice, J., Tredennick, A., Joyce, L.A., 2012. Climate change on the Shoshone National
Forest, Wyoming: a synthesis of past climate, climate projections, and ecosystem
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
10

implications. Gen. Tech. Rep. RMRS-GTR-274. U.S. Forest Service, Rocky Mountain
Research Station, Fort Collins, CO.
Safeeq, M., Grant, G.E., Lewis, S.L., Kramer, M., Staab, B., 2014. A hydrogeologic fra-
mework for characterizing summer streamflow sensitivity to climate warming in the
Pacific Northwest, USA. Hydrol. Earth Syst. Sci. 18, 3693–3710.
Safeeq, M., Grant, G.E., Lewis, S.L., Staab, B., 2015. Predicting landscape sensitivity to
present and future floods in the Pacific Northwest, USA. Hydrol. Process. 29,
5337–5353.
Safeeq, M., Grant, G.E., Lewis, S.L., Tague, C.L., 2013. Coupling snowpack and ground-
water dynamics to interpret historical streamflow trends in the western United States.
Hydrol. Process. 27, 655–668.
Salathé, E.P., Hamlet, A.F., Mass, C.F., et al., 2014. Estimates of twenty-first-century flood
risk in the Pacific Northwest based on regional climate model simulations. J.
Hydromet. 15, 1881–1899.
Schmidt, K., Roering, J.J., Stock, J.D., et al., 2001. The variability of root cohesion as an
influence on shallow landslide susceptibility in the Oregon Coast Range. Can.
Geotech. J. 38, 995–1024.
Schuster, R.L., Highland, L.M., 2003. Impact of landslides and innovative landslide-mi-
tigation measures on the natural environment. In: Lee, C.F., Tham, L.G. (Eds.),
Proceedings of the international conference on slope engineering. University of Hong
Kong, Hong Kong, China, pp. 64–74.
Stewart, I.T., Cayan, D.R., Dettinger, M.D., 2005. Changes toward earlier streamflow
timing across western North America. J. Clim. 18, 1136–1155.
Strauch, R.L., Raymond, C.L., Hamlet, A.F. 2014. Climate change, hydrology, and access
in the North Cascade Range. In: Raymond, C.L., Peterson, D.L., Rochefort, R.M., eds.
Climate change vulnerability and adaptation in the North Cascades region. Gen.
Tech. Rep. PNW-GTR-892. U.S. Forest Service, Pacific Northwest Research Station,
Portland OR, pp. 45–112.
Sumioka, S.S., Kresch, D.L., Kasnick, K.D., 1998. Magnitude and frequency of floods in
Washington. Water Resour. Invest. Rep. 97-4277. U.S. Geological Survey,
Tacoma, WA.
Tague, C., Grant, G.E., 2009. Groundwater dynamics mediate low-flow response to global
warming in snow-dominated alpine regions. Water Resour. Res. 45, W07421.
Tohver, I., Hamlet, A.F., Lee, S., 2014. Impacts of 21st century climate change on hy-
drologic extremes in the Pacific Northwest region of North America. J. Am. Water
Resour. Assoc. 50, 1461–1476.
Trombulak, S.C., Frissell, C.A., 2000. Review of ecological effects of roads on terrestrial
and aquatic communities. Conserv. Biol. 14, 18–30.
Tonina, D., Luce, C.H., Rieman, B., et al., 2008. Hydrological response to timber harvest
in northern Idaho: Implications for channel scour and persistence of salmonids.
Hydrol. Process. 22, 3223–3235.
U.S. Forest Service (USFS), 2010. National visitor use monitoring results: USDA Forest
Service national summary report. U.S. Forest Service, Washington, DC. http://www.
fs.fed.us/recreation/programs/nvum/nvum_national_summary_fy2009.pdf (accessed
16.06.18).
Vose, J.M., Clark, J.S., Luce, C.H., 2016. Introduction to drought and US forests: impacts
and potential management responses. For. Ecol. Manage. 380, 296–298. http://dx.
doi.org/10.1016/j.foreco.2016.09.030.
Walker, L., Figliozzi, M., Haire, A., MacArthur, J., 2011. Identifying surface transporta-
tion vulnerabilities and risk assessment opportunities under climate change: case
study in Portland, Oregon. Transport. Res. Rec.: J. Transport. Res. Board 2244,
41–49.
Wemple, B.C., Jones, J.A., 2003. Runoffproduction on forest roads in a steep, mountain
catchment. Water Resour. Res. 39 (8), 1220. http://dx.doi.org/10.1029/
2002WR001744.
Wemple, B.C., Swanson, F.J., Jones, J.A., 2001. Forest roads and geomorphic process
interactions: Cascade Range, Oregon. Earth Surface Process. Landforms 26 (2),
191–204.
Wenger, S.J., Isaak, D.J., Dunham, J.B., et al., 2011a. Role of climate and invasive species
in structuring trout distributions in the interior Columbia River Basin, USA. Can. J.
Fish Aquat. Sci. 68, 988–1008.
Wenger, S.J., Isaak, D.J., Luce, C.H., et al., 2011b. Flow regime, temperature, and biotic
interactions drive differential declines of trout species under climate change. Proc.
Nat. Acad. Sci. U.S.A. 108, 14175–14180.
Wenger, S.J., Luce, C.H., Hamlet, A.F., et al., 2010. Macroscale hydrologic modeling of
ecologically relevant flow metrics. Water Resour. Res. 46, W09513.
Wigmosta, M.S., W.A. Perkins, 2001. Simulating the effects of forest roads on watershed
hydrology, in Land Use and Watersheds: Human Influence on Hydrology and
Geomorphology in Urban and Forest Areas, M.S. Wigmosta and S.J. Burges, eds., AGU
Water Science and Application Volume 2, pp. 127–143.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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