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

  • USDA Forest Service and Oregon State University

Abstract and Figures

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.
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Climate Services
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Eects of climate change on hydrology and water resources in the Blue
Mountains, Oregon, USA
Caty F. Clifton
, Kate T. Day
, Charles H. Luce
, Gordon E. Grant
, Mohammad Safeeq
Jessica E. Halofsky
, Brian P. Staab
U.S. Forest Service, Pacic Northwest Region, Portland, OR, USA
U.S. Forest Service, Colville National Forest, Colville, WA, USA
U.S. Forest Service, Rocky Mountain Research Station, Boise, ID, USA
U.S. Forest Service, Pacic Northwest Research Station, Corvallis, OR, USA
Sierra Nevada Research Institute, University of California, Merced, CA, USA
University of Washington, School of Environmental and Forest Sciences, Seattle, WA, USA
Climate change
Low ows
Peak ows
Forest roads
Water supply
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 aected 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
ows occurring more commonly in late autumn and winter rather than spring, and lower low ows in summer,
phenomena that may already be occurring in the Pacic Northwest. Higher peak ows are expected to increase
the frequency and magnitude of ooding, which may increase erosion and scouring of the streambed and
concurrent risks to roads, culverts, and bridges. Mapping of projected peak ow changes near roads gives an
opportunity to mitigate these potential risks. Diminished snowpack and low summer ows are expected to cause
a reduction in water supply for aquatic ecosystems, agriculture, municipal consumption, and livestock grazing,
although this eect will not be as prominent in areas with substantial amounts of groundwater. Advanced
planning could help reduce conict 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 ecient and eective 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,
specically 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 aect ecological pro-
cesses and human enterprises in the region.
A higher rain:snow ratio in the Blue Mountains is expected
to cause higher peak streamows in late autumn and winter,
leading to increased frequency and magnitude of ooding
downstream. This will have the potential to damage roads,
especially in and near oodplains, and associated infra-
structure such as culverts and bridges. Retting this infra-
structure for more severe conditions will create a nancial
burden for the U.S. Forest Service, other public agencies, and
private landowners. Increase ooding 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 ows in
spring and summer. This will lead to lower streamows in
summer in both rivers and smaller streams, creating adverse
conditions for coldwater sh species and other aquatic
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: (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 (
Please cite this article as: Clifton, C.F., Climate Services (2018),
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 conicts are occasional and lo-
calized. However, competition among dierent 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 conicts. Finding a balance in
the near term among water allocated for ecological functions,
local communities, and economic benets will help forestall
those conicts.
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, aecting 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
Pacic Northwest region of North America, thereby aecting key re-
sources and processes including water supply, infrastructure, aquatic
habitat, and access. A warmer climate will aect 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 aect
snowpack volume (Hamlet et al., 2005; Luce et al., 2014a), streamow
(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 aect vegetation
(Kerns et al., 2018), which would in turn aect 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 aect 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 aects local economic activities, planning, and resource man-
agement. Anticipatory planning can reduce conicts and improve eco-
nomic and ecological outcomes during droughts. Damage to roads,
bridges, and culverts creates safety hazards, aects 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
streamow, low streamow, and stream temperatures), and projected
eects 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. Eects of climate change on hydrologic processes
2.1. Methods
Hydrologic simulations of streamow were prepared using the
Variable Inltration Capacity (VIC) model (Liang et al., 1994) to si-
mulate streamow 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 2040scover an average from 2030 to 2059, and the
2080scover 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 ow 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 coecient values of Safeeq et al. (2014) to
estimate impacts to low ows, which are sensitive to groundwater dy-
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 Pacic 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 eects (Lute and Luce, 2017).
Stream temperature changes were projected using the The NorWeST
Regional Stream Temperature Database (
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. Eects of climate change on snowpack
The role of snow in watershed runoin the Pacic 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-
ows 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 (1040% of
October-March precipitation), and are typically slightly below freezing
in mid-winter. These basins have multiple seasonal streamow peaks.
Snow-dominated basins are cold in winter, capturing > 40% of Oc-
tober-March precipitation as snow and have low ows through winter,
often with streamow peaks in spring. The Blue Mountain region has all
three types of basins.
Over the last 50 years, increasing temperatures in the Pacic
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-
nicant 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
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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. Eects of climate change on peak ows
Flooding in mountain watersheds in the Pacic Northwest is sensi-
tive to precipitation intensity, temperature (as it aects rain vs. snow),
and the combined eects 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 ooding and mass wasting events
(such as landslides, gullies, and debris ows), particularly after wildre
(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 ood risk depending on
local conditions in dierent 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
ooding 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
Higher temperatures in the latter half of the 20th century have
caused earlier runoin 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
ood 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 ow events
during winter are projected to change substantially in some areas, and
areas with the largest change in ood magnitude (Fig. 3) also have
altered frequency of those high ows occurring during winter months
(Fig. 4), which may be damaging for sh 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 ow 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 ood magnitude increases. Other areas in
the ecoregion already experience substantial rain-on-snow.
2.4. Eects of climate change on low ows
Earlier snowmelt over the last 50 years has reduced spring, early
summer, and late summer ows in the western United States (Leppi
et al., 2011; Safeeq et al., 2013; Kormos et al., 2016). The 25th per-
centile ows (drought year ows, 19482006) have become even lower
across the Pacic Northwest (Luce and Holden, 2009), and large de-
creasing fractional ows have been documented for eastern Oregon in
March-June (Stewart et al., 2005). Summer low ows are aected by
both snowmelt and landscape drainage eciency (Tague and Grant,
2009; Safeeq et al., 2013). In the Blue Mountains, which have a mod-
erate groundwater component, summer ows decreased 2128% 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 streamow
Fig. 1. National Forests and major basins in the Blue Mountains Ecoregion.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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 ows
using the hydrologic simulations indicate small decreases in summer
streamow (< 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% streamow decreases by 2080. Note that many of
the most sensitive areas for low ows 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 runo, and
small changes in snowpack drive large changes in low ow (Safeeq
et al., 2014).
2.5. Eects of climate change on water quality
Historical temperatures in unregulated streams across the Pacic
Northwest paralleled air temperature trends at nearby weather stations
from 1980 to 2009 (Isaak et al., 2010, 2012), and stream temperatures
increased signicantly in summer, autumn, and winter, with the highest
rates of warming in summer (reconstructed trend of 0.22 °C per
decade). A signicant 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 (8090%) was explained by air temperature trends
and a smaller proportion by discharge (1020%). A separate study of
stream data found variable trends in stream temperature, with
increased temperature at some sites in the Pacic Northwest (2844%)
and decreased temperature at others (2233%) (Arismendi et al., 2012).
Discrepancies are attributed to dierences 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 wildre area
burned (Littell et al., 2009; Littell et al., 2016). Increased wildre,
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 wildre 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 dierent
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
ows, 9% for wildlife, 5% for irrigation, and 3% for domestic use (320
points of diversion) (Gecy, 2014). Instream ows 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-
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 aect local hydrology and in some
cases ecological functions (Dwire et al., 2018). It is uncertain how long-
term warming or short-term droughts will aect permitted water use,
although signicant 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 streamow 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 ows in
summer. Because water supply in summer is limited, climate change
may make it dicult to meet current demands during extreme drought
years and following consecutive drought years, especially after the mid
21st century. Current conict over water use in the Blue Mountains
region is not a prominent issue, although future water shortages caused
by declines in dry season ows may create social and political tension if
dierent sectors (e.g., agriculture and municipal) compete for water.
Declining summer ows caused by reduced snowpack accumulation
and earlier snowmelt in the Blue Mountains could aect 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 ows 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 aected 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 streamow.
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) classication system used to rate wa-
tershed condition in national forests (Potyondy and Geier, 2011). Most
sub-watersheds in the Blue Mountains are rated as functioningor
functioning at risk,based on ow alterations from diversions, with-
drawals, and dams relative to natural ows and groundwater storage.
The Burnt, Powder, Upper Grande Ronde, and Wallowa sub-basins have
the most sub-watersheds with impaired functionfor water quantity.
The highest o-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 ows (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 ood magnitude between the historical period (19701999) and the 2080s for the Blue Mountains region.
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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, o-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 ood. Road construction has
declined since the 1990s, with few new roads being added. Roads ac-
celerate runorates and decrease late-season ows, increase peak
ows, 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 aect surface and subsurface ows and erosion (Luce,
2002; Trombulak and Frissell, 2000).
National forest engineering staare 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-proong 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,
The Malheur, Umatilla, and Wallow-Whitman National Forests are
currently identifying a sustainable road network that is ecologically and
scally 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 agencys ability to acquire funding for road
improvement and decommissioning, provides a framework for annual
maintenance costs, facilitates agreement with regulatory agencies, and
increases nancial 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 ow. This addresses whether high ow events typically
occur in winter (December-March), when fall spawning sh have eggs in the gravel, or in other months. Values are displayed the historical period (19701999) (left)
and projected for 2080 (right).
C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
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 eects on transportation systems
Climate and hydrology will inuence the transportation system in
the Blue Mountains through reduced snowpack, resulting in a longer
season of road use, higher peak ows and ood risk (Fig. 7), and in-
creased landslide risk (Strauch et al., 2014). Increased wildre dis-
turbance (Kerns et al., 2018) plus higher peak ows may contribute to
increased erosion and landslides (Goode et al., 2012). Direct (physical)
eects of climate change occur from oods, snow, landslides, extreme
temperatures, and wind, whereas indirect eects include secondary
inuences on access related to public safety and visitor use patterns.
Eects 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 eects on hydrologic
systems and may require changes of current design standards for in-
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
2575 years, and if they are beyond their design life, rust and wear
make them less resilient to high ows 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 runoand peak ows (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 ooding, channel migration, and bank erosion. Most road-
stream crossings use culverts rather than bridges, and culverts are more
sensitive to high streamows 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 insucient to maintain and repair
infrastructure, thus increasing the susceptibility of the transportation
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 sh passage and stream function.
Fig. 5. Projected change in mean summer streamow from the historic time period (19701999) 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
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 eects on other infrastructure and access
In the short-term changes in runoand geomorphology will directly
challenge the road network integrity. Higher peak ows in winter in-
crease the potential impacts of ooding roads, trails, campgrounds, and
structures (Walker et al., 2011; MacArthur et al., 2012). Increased risk
of landslides in some areas will contribute to ooding by diverting
water, blocking drainage, and lling 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 streamows could create
hazardous conditions for river recreation and campers. More wildres
(Kerns et al., 2018) would further restrict emergency access by in-
creasing downed logs and road damage, reducing agency capacity to
respond to additional res and to emergency needs in local commu-
nities (Strauch et al., 2014).
4.4. Medium and long-term eects on access
As change progresses, runoand geomorphic impacts could become
more severe and widespread, and accumulated minor impacts will ex-
acerbate the outcomes. More frequent ooding will continue to increase
sediment and debris transport, damaging stream-crossing structures.
Shifting channel dynamics caused by increased ow and sediment may
compound problems, even if crossing structures are upgraded to ac-
commodate higher ows. Repeated landslides can cause aggradation in
streams, thus elevating future ood potential, and culverts blocked with
debris can cause ooding 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 wildre and insect outbreaks (Montgomery
et al., 2000; Schmidt et al., 2001; Istanbulluoglu et al., 2004). Although
oods 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 streamows in
Fig. 6. Projected risk of summer water shortage in the Blue Mountains region, based on low streamows for 2080s. The data in Fig. 5 were used to calculate
dierences averaged over each watershed.
Table 1
Kilometers of road by maintenance level in national forests in the Blue
Operational maintenance levels National forests
Malheur Umatilla Wallowa-Whitman
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
late summer (Mickelson, 2009), as well as hazards associated with
deposited sediment and woody debris from high winter ows. Warmer
winters may shift river recreation to times of the year when risks of
extreme weather and ooding are higher.
Some benets to access and transportation in the Blue Mountains
may accrue from the eects 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 signicant 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.
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 benetted from the ad-
vice of two anonymous reviewers.
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C.F. Clifton et al. Climate Services xxx (xxxx) xxx–xxx
... Timber and other forest products, as well as recreation and wildlife, are an important source of income for local economies (Hamilton et al 2016). Increasing air temperatures over the last several decades has reduced late spring snowpack as well as summer soil and fuel moisture (Stewart et al 2005;Hamlet et al 2007;Clifton et al 2018), and these trends are expected to continue (Davis et al 2017). Increased fire activity is expected to catalyze changes in dry to moist mixed conifer forest communities, such as decreases in forested area, lower canopy cover within forested areas, and shifts toward more drought-tolerant species (Kerns et al 2018). ...
... Expected effects ("+" positive, "-" negative, "NT" not tested) were based on prior studies (see superscript numbers and footnotes) in the Blue Mountains ecoregion or neighboring ecoregions a (Boag et al, 2020) b (Downing et al, 2019) c (Povak et al 2020) d (Littlefield 2019) 1970-1999. Annual precipitation has not significantly changed, and model projections do not agree on the direction of change in future annual precipitation (Clifton et al 2018). Soils are ashy loamy sand derived from basalt layers, loess deposits, and volcanic ash (NRCS 2012). ...
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Background In seed-obligate conifer forests of the western US, land managers need a better understanding of the spatiotemporal variability in post-fire recovery to develop adaptation strategies. Successful establishment of post-fire seedlings requires the arrival of seeds and favorable environmental conditions for germination, survival, and growth. We investigated the spatiotemporal limitations to post-fire seedling establishment and height growth in dry to moist mixed conifer forests with and without post-fire forest management treatments (salvage logging, grass seeding) in areas burned from low to high severity. In 2011, we measured post-fire seedling establishment year, juvenile density (seedlings and saplings), and height growth (annual and total) in 50 plots with six conifer species in the School Fire (2005), Blue Mountains, WA, USA. In 2021, we remeasured the plots for post-fire juvenile density and height growth. Results Post-fire juvenile tree densities appeared sufficient for self-replacement of forest (> 60 stems ha ⁻¹ ) in 96% of plots in 2021 (median 3130 stems ha ⁻¹ ), but densities were highly variable (range 33–100,501 stems ha ⁻¹ ). Annual seedling establishment was positively correlated with cooler, wetter climate conditions during the summer of germination (July–September) and the growing season of the subsequent year (April–September) for multiple tree species. We found lower juvenile densities at greater distances to seed sources and with higher grass cover, while salvage logging had no effect. Annual height growth was shorter on warmer, drier topographic positions for three species, whereas annual height growth was associated with climate variability for one species. Shifts in height class structure from 2011 to 2021 were, in part, explained by differences among species in annual height growth. Conclusions Abundant and widespread tree seedling establishment for multiple conifer species after fire was strong evidence that most burned sites in the present study are currently on a trajectory to return to forest. However, post-fire establishment may be constrained to brief periods of cooler, wetter climate conditions following future fires. Long-term monitoring of post-fire recovery dynamics is needed to inform management activities designed to adapt forests to climate change and future disturbances, which will collectively shape future forest structure and composition.
... Snowpack acts as a seasonal high mountain water reservoir, recharging aquifers and nourishing the rivers, streams, and tributaries into the summer and fall following snowmelt [1][2][3], providing important moisture for soils and vegetation. A warming climate has reduced snowpack volume [4][5][6], advanced the timing of spring snowmelt [5,7,8], limited downstream water availability [1,7,9], and ultimately reduced summer soil moisture [10]. Moreover, due to climate warming, forest fires are increasing in intensity, extent, frequency, and duration across the western US, particularly during early snowmelt years [11][12][13]. ...
... Snowpack acts as a seasonal high mountain water reservoir, recharging aquifers and nourishing the rivers, streams, and tributaries into the summer and fall following snowmelt [1][2][3], providing important moisture for soils and vegetation. A warming climate has reduced snowpack volume [4][5][6], advanced the timing of spring snowmelt [5,7,8], limited downstream water availability [1,7,9], and ultimately reduced summer soil moisture [10]. Moreover, due to climate warming, forest fires are increasing in intensity, extent, frequency, and duration across the western US, particularly during early snowmelt years [11][12][13]. ...
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Surface snow albedo (SSA) darkens immediately following a forest fire, while landscape snow albedo (LSA) brightens as more of the snow-covered surface becomes visible under the charred canopy. The duration and variability of the post-fire snow albedo recovery process remain unknown beyond a few years following the fire. We evaluated the temporal variability of post-fire snow albedo recovery relative to burn severity across a chronosequence of eight burned forests burned from 2000 to 2019, using pre- and post-fire daily, seasonal, and annual landscape snow albedo data derived from the Moderate Resolution Imaging Spectroradiometer (MOD10A1). Post-fire annual LSA increased by 21% the first year following the fire and increased continually by 33% on average across all eight forest fires and burn severity classifications over the period of record (18 years following a fire). Post-fire LSA measurements increased by 63% and 53% in high and moderate burn severity areas over ten years following fire. While minimum and maximum snow albedo values increased relative to annual post-fire LSA recovery, daily snow albedo decay following fresh snowfall accelerated following forest fire during the snowmelt period. Snow albedo recovery over 10 years following fire did not resemble the antecedent pre-fire unburned forest but more resembled open meadows. The degradation of forest canopy structure is the key driver underlying the paradox of the post-fire snow albedo change (SSA vs. LSA).
... This is because transitional river basins face large increases in winter streamflow. While many studies have generally focused on mountainous and arctic regions [23][24][25][26], relatively fewer studies have reported on snow hydrology changes across low-relief topography regions [27,28]. These are regions in which the river runoff is also sensitive to the effects of the changing patterns of snow accumulation and melt. ...
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The rapidly changing climate affects vulnerable water resources, which makes it important to evaluate multi-year trends in hydroclimatic characteristics. In this study, the changes in cold-season temperature (November-April) were analyzed in the period of 1951-2021 to reveal their impacts on precipitation and streamflow components in the Liwiec River basin (Poland). The temperature threshold approach was applied to reconstruct the snowfall/rainfall patterns. The Witten-berg filter method was applied to the hydrograph separation. The Mann-Kendall test and Sen's slope were applied to estimate the significance and magnitude of the trends. An assessment of the similarity between trends in temperature and hydroclimatic variables was conducted using the Spearman rank-order correlation. The shift-type changes in river regime were assessed via the Krus-kal-Wallis test. The results revealed that temporal changes in both snowfall, rainfall, and baseflow metrics were significantly associated with increasing temperature. Over 71 years, the temperature rose by ~2.70 °C, the snowfall-to-precipitation ratio decreased by ~16%, the baseflow increased with a depth of ~17 mm, and the baseflow index rose by ~18%. The river regime shifted from the snow-dominated to the snow-affected type. Overall, this study provides evidence of a gradual temperature increase over the last seven decades that is affecting the precipitation phase and streamflow component partitioning in the middle-latitude region.
... Because they see two-thirds of their yearly precipitation and because snow and ice build up as water reservoirs, spring and winter are crucial seasons in the Himalayan area(Kulkarni et al., 2021). Altered precipitation patterns during these months can induce water shortages in summer, effect agricultural yields in autumn, and modify snow-regimes(Viviroli et al., 2011;Chai et al., 2016;Clifton et al., 2018). However, our data does not reveal any signi cant changes in Maximum temperature. ...
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Planning agricultural practises relies entirely on the timely prediction of rainfall based on data analysis. Early forecasting aids in the preparation of disaster management plans in high-risk locations in the event of predicted severe or limited rainfall. In this study, we analyzed the trends of precipitation and climatic variability for of Jammu region from 1925-2020. The non-parametric Mann-Kendall test was used to analyze the significance of trends in precipitation data on monthly seasonal and annual scales, whereas the non-parametric Sens’s estimator of the slope was used to quantify the magnitude of climatic trends. The results revealed that the Jammu region shows a statistically significant positive (p <0.005) for annual mean precipitation. In annual trend magnitude, the Jammu region showed a statistically significant increasing trend of 0.5260079 mm a ⁻¹ for the observed 95 years' climatic time series. The seasonal trends of precipitation statistics exhibit statistically significant positive trends over the observed time series in the case of the summer season only. Further, a significant precipitation increase of 1.484841 mm ⁻¹ was observed for the summer season only. The results of Pettit’s test for detecting annual change points for precipitation show a statistically significant change in the years 1988, 1951, and 1985 and seasonally in the year 1993 for the summer season only. Further, the results of the Mann–Kendall test for detecting monthly trends in the precipitation variables for the 95 years of observed climatic time series exhibit a statistically significant increasing trend for the months of May, June, August, and November. The results of this study are extremely useful in many sectors including agriculture, water resources, and most notably climatology studies in most striking aspects of developmental planning in recent times.
... Higher temperatures cause increasing atmospheric water demand, which, in turn, changes precipitation timing and amount, affecting snow season (Gergel et al., 2017), snowmelt (Hakala et al., 2018) and timing of consequent streamflow (Clow, 2010). Concurrent shifts in precipitation and temperature impact the availability and access to water (Clifton et al., 2018), while also influencing the timing and magnitude of extreme events, such as floods or droughts (Dankers et al., 2014;Dankers and Feyen, 2009;Villarini and Wasko, 2021). ...
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Climate change poses undeniable impacts on hydroclimatic processes due to simultaneous effects of rising temperature and changing precipitation patterns. To quantify these impacts, simulations of climate variables are typically retrieved from climate models, which are then downscaled and bias-adjusted for a particular study site. The literature holds various methods for bias adjustment, ranging from simple univariate methods that only adjust one variable at a time, to more advanced multivariate methods that additionally consider the dependence between variables. There is, however, still no guidance for choosing appropriate bias adjustment methods for a study at hand. In particular, the question whether the benefits of potentially improved adjustments outweigh the cost of increased complexity, remains unanswered. This thesis primarily sought to provide an answer to this question by offering practical guidelines for the application of uni- and multivariate bias-adjustment methods in hydrological climate-change impact studies. To this end, the thesis includes a practice-oriented overview of copulas, one of the most widely used multivariate methods in climate-change studies. Furthermore, it presents an evaluation of two commonly used parsimonious univariate and two advanced multivariate methods. The assessment focused on their ability to reproduce numerous statistical properties of precipitation and temperature series, and on the cascading effects on simulated hydrologic signatures. The thesis culminates in a practical application of one bias adjustment method as part of a modeling chain to quantify future droughts. The results elucidate that all bias adjustment methods generally improved the raw climate model simulations, but not a single method consistently outperformed all other methods. Univariate methods generally adjusted the simulations reasonably well, while multivariate methods were favorable only for particular flow regimes. Thus, other practical aspects such as computational time and theoretical requirements should also be taken into consideration when choosing an appropriate bias adjustment method.
... In dry and semi-arid regions of the world, water is a limited resource, limiting the range of plant and animal species (Clifton et al. 2018). Water is also an important component of human activity, influencing where and how human communities and local economies thrive across the landscape (Barros et al. 2021). ...
... In montane headwater basins, transport of suspended sediment primarily occurs during storm events and snowmelt periods (Wipfli et al., 2007). As the climate continues to warm in many montane areas, snow-dominated regimes will shift towards more raindominated regimes (Clifton et al., 2018;Klos et al., 2014;. This will increase high-flow events during the wet season (Safeeq et al., 2015;, followed by a greater and faster transport of suspended sediment (Ares et al., 2016;Buendia et al., 2016). ...
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Suspended sediment transport in montane headwaters is important to water quality and nutrient balances. However, predictions of sediment source and transport can be difficult, in part, because of a changing climate and increasing frequencies of disturbances. We used observations from ten headwater streams in Water Year (WY; starting on October 1st and ending on September 30th) 2007–2009 and 2013–2018 to determine the potential impacts of climate and forest management on suspended sediment delivery. We analyzed hysteretic responses of suspended sediment for 76 events in five headwater catchments within a snow‐dominated site and another five within a lower‐elevation, rain‐snow transition site, in the mixed‐conifer zone of California's Sierra Nevada. Hysteresis patterns were predominantly clockwise at both sites, suggesting localized sediment sources such as streambeds and banks. The warmer, transition site exhibited a lower proportion of clockwise‐loop events, faster transport speed, and higher peak sediment concentrations than the snow‐dominated site. This suggests extended sediment sources and increases in transport can occur as currently snow‐dominated areas become rain‐snow transitional. Over the nine water years, we observed similar hysteresis effects among years under drought, near‐average, and extremely wet conditions. Hence, fluctuations in precipitation amounts across years may not influence sediment source area substantially. Furthermore, we compared hysteresis metrics between the control, thin only, burn only, and thin combined with burn catchments during the post‐treatment period (WY 2013–2018). Hysteresis effects remained unchanged among treatments, which may be attributed to the combinations of low‐intensity operations implemented with best management practices combined with a four‐year drought (WY 2013 – 2016). Taken together, sediment sources in small headwater catchments will probably remain localized with changing precipitation levels and low‐intensity management operations, but it may be extended and potentially lead to higher sediment yields as the main hydrologic input shifts from primarily snow to a mix of rain and snow. This article is protected by copyright. All rights reserved.
... As much as it affects the physical sphere, likewise, it profoundly impacts the anthropogenic domains, some of them being: health and well-being (Leal Filho et al., 2018;Thomas et al., 2014), forage supply (Ferner et al., 2018), and food systems (Butler, 2010;Ebi et al., 2010). Moreover, the rise in climate change related variabilities and extreme events like changes in precipitation patterns, heat waves, and cold spells, along with the trend toward warming temperatures, induce hydrological changes and impacts on water resources (Clifton et al., 2018;Meng et al., 2016;Nan et al., 2011;Prasad Devkota & Raj Gyawali, 2015); temperature-related mortality (Dear & Wang, 2015;Heaviside et al., 2016); disruption in essential services like public transit systems (Miao et al., 2018); and even instances of conflict and forced migration (Abel et al., 2019), all amplifying risk to the human sphere. ...
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The present century faces developmental fallout as vulnerability and risk mount on the global systems due to climate change, urbanisation, and population ageing. Moreover, population ageing is gaining a stronger hold in urban areas, and so are climate change and related shocks and stresses. Consequently, repercussions for the weakest sections of society – including the elderly – remain under academic consideration. In this context, the paper aims to understand the perilous predicament of older people due to the occurrence and interaction between climate change, urbanisation, and population ageing. This review investigates the underpinnings of the nature of the interaction among the three phenomena; and discerns how as a result of the interaction, various climate change related shocks and stresses affect older people in urban settings. It emerges that these three phenomena exhibit: concurrence; a positive trend of growth; and a cyclic pattern of interaction with four linkages, implying (i) rapid urbanisation is fuelling climate change, (ii) climate change is impacting urban areas, (iii) older people are increasing in urban areas, and (iv) urbanisation provides opportunities and barriers for older people. This interplay further discloses that older people stand vulnerable and at heightened risk from climate change related stressors in urban areas. These understandings highlight the need to ensure that urban environments remain age-friendly even in the face of climate change.
Environment and climate changes have been posing pressure on the quality and quantity of water resources. The research examined the hydrological response of upper Awash River basin under the influences of environmental and climate changes. The climate change results up to 77.5% and 100.5% increament in annual and wet season monthly river flow, respectively when using projected climate data of RCP4.5. Whereas, the land use change alterss river flow in a one digit percentile increment/ decrement. It was observed that effects of both climate and land use changes will likely to increase the river flow and possibly cause flooding in the upper Awash River basin. The land use change impact can be alleviated by implementing appropriate land use management practices . The climate change mitigation needs long term process; as a result climate change adaptation mechanisms are recommended for the short term while employing climate mitigation options in the long run.
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Riparian areas, wetlands, and groundwater-dependent ecosystems, which are found at all elevations throughout the Blue Mountains, comprise a small portion of the landscape but have high conservation value because they provide habitat for diverse flora and fauna. The effects of climate change on these special habitats may be especially profound, due to altered snowpack and hydrologic regimes predicted to occur in the near future. The functionality of many riparian areas is currently compromised by water diversions and livestock grazing, which reduces their resilience to additional stresses that a warmer climate may bring. Areas associated with springs and small streams will probably experience near-term changes, and some riparian areas and wetlands may decrease in size over time. A warmer climate and reduced soil moisture could lead to a transition from riparian hardwood species to more drought tolerant conifers and shrubs. Increased frequency and spatial extent of wildfire spreading from upland forests could also affect riparian species composition. The specific effects of climate change will vary, depending on local hydrology (especially groundwater), topography, streamside microclimates, and current conditions and land use.
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There is a growing consensus that climate is changing, but beliefs about the causal factors vary widely among the general public. Current research shows that such causal beliefs are strongly influenced by cultural, political, and identity-driven views. We examined the influence that local perceptions have on the acceptance of basic facts about climate change. We also examined the connection to wildfire by local people. Two recent telephone surveys found that 37% (in 2011) and 46% (in 2014) of eastern Oregon (USA) respondents accept the scientific consensus that human activities are now changing the climate. Although most do not agree with that consensus, large majorities (85-86%) do agree that climate is changing, whether by natural or human causes. Acceptance of anthropogenic climate change generally divides along political party lines, but acceptance of climate change more generally, and concerns about wildfire, transcend political divisions. Support for active forest management to reduce wildfire risks is strong in this region, and restoration treatments could be critical to the resilience of both communities and ecosystems. Although these immediate steps involve adaptations to a changing climate, they can be motivated without necessarily invoking human-caused climate change, a divisive concept among local landowners.
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We used autecological, paleoecological, and modeling information to explore the potential effects of climate change on vegetation in the Blue Mountains ecoregion, Oregon (USA). Although uncertainty exists about the exact nature of future vegetation change, we infer that the following are likely to occur by the end of the century: (1) dominance of ponderosa pine and sagebrush will increase in many locations, (2) the forest-steppe ecotone will move upward in latitude and elevation, (3) ponderosa pine will be distributed at higher elevations, (4) subalpine and alpine systems will be replaced by grass species, pine, and Douglas-fir, (5) moist forest types may increase under wetter scenarios, (6) the distribution and abundance of juniper woodlands may decrease if the frequency and extent of wildfire increase, and (7) grasslands and shrublands will increase at lower elevations. Tree growth in energy-limited landscapes (high elevations, north aspects) will increase as the climate warms and snowpack decreases, whereas tree growth in water-limited landscapes (low elevations, south aspects) will decrease. Ecological disturbances, including wildfire, insect outbreaks, and non-native species, which are expected to increase in a warmer climate, will affect species distribution, tree age, and vegetation structure, facilitating transitions to new combinations of species and vegetation patterns. In dry forests where fire has not occurred for several decades, crown fires may result in high tree mortality, and the interaction of multiple disturbances and stressors will probably exacerbate stress complexes. Increased disturbance will favor species with physiological and phenological traits that allow them to tolerate frequent disturbance.
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National forests in the Blue Mountains (USA) region have developed adaptation options that address effects identified in a recent climate change vulnerability assessment. Adaptation strategies (general, overarching) and adaptation tactics (specific, on-the-ground) were elicited from resource specialists and stakeholders through a workshop process. For water supply and infrastructure, primary adaptation strategies restore hydrologic function of watersheds, connect floodplains, support groundwater-dependent ecosystems, maximize valley storage, and reduce fire hazard. For fisheries, strategies maintain or restore natural flow regimes and thermal conditions, improve water conservation, decrease fragmentation of stream networks, and develop geospatial data on stream temperature and geologic hazards. For upland vegetation, disturbance-focused strategies reduce severity and patch size of disturbances, protect refugia, increase resilience of native vegetation by reducing non-climate stressors, protect genotypic and phenotypic diversity, and focus on functional systems (not just species). For special habitats (riparian areas, wetlands, groundwater-dependent ecosystems), strategies restore or maintain natural flow regimes, maintain appropriate plant densities, improve soil health and streambank stability, and reduce non-climate stressors. Prominent interactions of resource effects makes coordination critical for implementation and effectiveness of adaptation tactics and restoration projects in the Blue Mountains.
Decades of quantitative measurement indicate that roots can mechanically reinforce shallow soils in forested landscapes. Forests, however, have variations in vegetation species and age which can dominate the local stability of landslide-initiation sites. To assess the influence of this variability on root cohesion we examined scarps of landslides triggered during large storms in February and November of 1996 in the Oregon Coast Range and hand-dug soil pits on stable ground. At 41 sites we estimated the cohesive reinforcement to soil due to roots by determining the tensile strength, species, depth, orientation, relative health, and the density of roots ≥1 mm in diameter within a measured soil area. We found that median lateral root cohesion ranges from 6.8-23.2 kPa in industrial forests with significant understory and deciduous vegetation to 25.6-94.3 kPa in natural forests dominated by coniferous vegetation. Lateral root cohesion in clearcuts is uniformly ≤10 kPa. Some 100-year-old industrial forests have species compositions, lateral root cohesion, and root diameters that more closely resemble 10-year-old clearcuts than natural forests. As such, the influence of root cohesion variability on landslide susceptibility cannot be determined solely from broad age classifications or extrapolated from the presence of one species of vegetation. Furthermore, the anthropogenic disturbance legacy modifies root cohesion for at least a century and should be considered when comparing contemporary landslide rates from industrial forests with geologic background rates.
The related challenges of predictions in ungauged basins and predictions in ungauged climates point to the need to develop environmental models that are transferable across both space and time. Hydrologic modeling has historically focused on modelling one or only a few basins using highly parameterized conceptual or physically based models. However, model parameters and structures have been shown to change significantly when calibrated to new basins or time periods, suggesting that model complexity and model transferability may be antithetical. Empirical space-for-time models provide a framework within which to assess model transferability and any tradeoff with model complexity. Using 497 SNOTEL sites in the western U.S., we develop space-for-time models of April 1 SWE and Snow Residence Time based on mean winter temperature and cumulative winter precipitation. The transferability of the models to new conditions (in both space and time) is assessed using non-random cross-validation tests with consideration of the influence of model complexity on transferability. As others have noted, the algorithmic empirical models transfer best when minimal extrapolation in input variables is required. Temporal split-sample validations use pseudoreplicated samples, resulting in the selection of overly complex models, which has implications for the design of hydrologic model validation tests. Finally, we show that low to moderate complexity models transfer most successfully to new conditions in space and time, providing empirical confirmation of the parsimony principal.