Integrating geology,
vegetation and snow
regimes in climate
change assessment for
the Western US
Christina Tague, Dept. of Geography, San Diego State University,
Gordon Grant, US Forest Service, Corvallis, Oregon
Lindsey Christensen, USGS, Natural Resource Ecology Lab, Fort Collins
Jill Baron, USGS, Natural Resource Ecology Lab, Fort Collins
How sensitive is summer water availability (as streamflow and soil
moisture for terrestrial ecological processes) to climate variability (in
the mountains of the Western US)?
How does this sensitivity vary in space? And across ‘relevant’ spatial
scales?
Mean Monthly Precipitation
North Cascade Region
(1895-1999)
20
10
Ju
n
Ju
l
Au
g
Se
p
O
ct
N
ov
D
ec
0
Ja
n
Fe
b
M
ar
Ap
r
M
ay
cm
30
RECHARGE: Spatial Structure of Snow Accumulation
Snowpack storage and subsequent
melt is the primary source of
recharge. Earlier snowmelt means
water leaves the system earlier in the
season and late summer streamflow
is reduced.
Spatial structure of “Snow-at-risk”
defined by elevation and latitude mid-elevation Sierras and
Cascades(Knowles and Cayan,
2004; Service et al. 2004; Mote et
al., 2005, Nolin et al. in press,
Hayhoe 2004; Payne et al. 2004)
Remaining questions - what are the
characteristic ‘resolution’ over which
gradients in snow accumulation and
melt must be defined to capture
significant differences in summer
streamflow?
Climate-hydrology interactions in Western US mountains
Processes and Drivers
High Cascades
Western Cascades
Will
am
ette
R
iver
Cl
ac
ka
m
N. Santiam
as
Drainage Efficiency:
Geology
Drained by large east-west
trending tributaries
(McKenzie and others)
Elevation range 132 -3150
meters (transition from rain
to snow-dominance)
S.Santiam
McKenzie
Tributaries cross two distinct
geologic regions
High Cascades
Western Cascades
High and Western Cascade streams: Distinctive
Summer Low Flow Regimes
High Cascade stream shows muted peaks but greater
summer baseflow with similar input precipitation
High Cascades
Western Cascades
High Cascades
„Recent
volcanic activity
(Pleistocene to present)
„Gently
sloping (shield
volcano) dominated
topography
„High vertical conductivity,
poorly developed soils,
„Low
density, disorganized
drainage networks,
combination of rapid shallow
subsurface and deep
groundwater drainage
High Cascades
Western Cascades
Western Cascades
„High
„Miocene
volcanic basalts
and andesites
„Steep, highly dissected
erosional topography
vertical conductivity
grading to shallow
subsurface clay, saprolite
confining layers
„High density, well
developed shallow
subsurface drainage
network
Empirical Analysis of USGS gage records for
High/Western Cascade streams
Log Mean August Streamflow
(mm/month)
5.0
Mean August Streamflow
4.5
4.0
3.5
Summer streamflow
recession characteristics
3.0
2.5
2.0
0%
20%
40%
60%
80%
High Cascades in Contributing Area
6
Average August Discharge, 2002
100%
Similar for stream
temperature
5
mm/day
4
3
Western Cascade
Stream s
High Cascade
Stream s
2
1
0
1
Predicted by percent High
Cascade geology in the
contributing area
Tague, C.L, and Grant, G. (2004) “A geological framework for interpreting the low flow regimes of Cascade
streams, Willamette River Basin, Oregon”, Water Resources Resarch, 40, W04303,
doi:10.1029/2003WR002629,
Tague et al (in press) , Hydrogeologic controls on summer stream temperatures in the McKenzie River basin,
OregonHydrologic Processes.
Implications of geologic-based classification and its
correlation with summer streamflow volumes and
temperatures
Are differences in streamflow volumes due to geologic
controls on flow or differences in elevation (more snow vs
rain in the High Cascades)?
Will these systems respond differently to climate
warming?
MODEL ANALYSIS of a High and Western Cascade
watersheds
Utilize RHESSys: spatially distributed physically based
model of coupled eco-hydrologic systems
http://geography.sdsu.edu/Research/Projects/RHESSYS/index.html
Tague and Band (2004) Earth Interactions
Modeling Case Study: Contrasting Watersheds
Snow
Precipitation
MRCL:
McKenzie
River at Clear
Lake, High
Cascade
(293km2)
MRCLGW
MRCL-SSF
LOC: Lookout
Creek, Western
Cascades
(64km2)
LOC
Rain
Slow
(Deeper
Groundwater)
Drainage
Fast
(Shallow
Subsurface)
100
Log og discharge (mm/day)
Western Cascade (LOC)
Modeled
Observed
10
1
st
gu
Au
ay
M
ch
M
ar
ry
nu
a
r
Ja
m
ve
No
pt
em
be
be
r
ne
Ju
ri l
Ap
High Cascade (MRCLGW, MRCL-SSF)
10
1
Observed
Modeled
0.1
ar
y
Ap
ril
Ju
ne
Au
gu
st
O
ct
o
De be r
ce
m
be
r
Ja
nu
ar
y
Ap
ril
Ju
ne
Au
gu
st
nu
Ja
ve
m
be
r
Modeled w/o gw
No
Log of discharge (mm/day)
100
Se
De
Fe
ce
br
m
ua
be
r
ry
0.1
Model allows us to
consider a hypothetical
watershed: High Cascade
(topography, vegetation,
climate, snow
accumulation and melt)
but Western Cascade
geology
RHESSys streamflow
estimates capture summer
streamflow distinctions
between High and Western
Cascades - and shows that
these are due primarily to
geologic controls on
drainage efficiency!!
Relative (percent) change in modelled
streamflow with a 1.5C warming scenario
Greatest reductions occur for Western Cascade system,
similar patterns obtained for a 2.5C warming
Reduction in modeled August Flow (as unit
discharge) with a 1.5C warming scenario
Greatest losses are now associated with High Cascade system
Relationship between modeled snowpack (water year
max 15-day average) and observed August
streamflow
High Cascade watershed
shows greater
increase in summer
flow with greater
modeled snow
Slope - High Cascade
(0.003) vs Western
Cascade (0.0004)
Both statistically
significant
Implications for climate change impacts on
water availability
High Cascade watersheds a) contribute a disproportionate amount of
flow in larger river basins and b) flow volumes are likely to be more
sensitive to climate warming
Large river water supply impacts (power generation, recreation,
water supply for irrigation)
Western Cascade watersheds, however, show greater relative
sensitivity of summer streamflow to climate warming (and are
warmer!)
Distributed headwater stream habitat impacts (aquatic habitat)
Differences in drainage efficiency are as important as topographic
differences in apriori snow accumulation and melt in controlling flow
regimes
Geologic framework in the Sierras - will it
matter there?
total water
input to soil
Southern Cascades
Volcanics
(Hat Creek)
Deep
Groundwater
Dominated
Sierra-volcanic
(Duncan Canyon
Creek)
Faster
Sierra-granitic
(Merced River;
Cole Creek )
Shallow
Sub-surface Flow
Dominated
Climate-hydrology interactions in Western US mountains
Processes and Drivers
How are important are spatial differences in plant water
use in understand spatial patterns of hydrologic
response to climate warming: summer streamflow?
Disturbance (Logging, Fire)
Spatial differences in plant
responses to warming
Initial increases in summer
streamflow following fire/logging
Changes in the timing and magnitude
of evapotranspiration
Longer term decreases in summer
streamflow with associated changes in
biomass and species in regrowth
While studies have shown how
biomass response to climate vary with
topography within the Western US,
fewer studies have explored the spatial
structure of ET response
RHESSys application
Model Patches
RHESSys couples estimation of ET
(Penman-Monteith) with soil moisture and
atmospheric/energy drivers.
900
800
700
precipitation (mm)
RHESSys used to estimate
changes in summer
streamflow with climate
variability for mature and
disturbed catchments
April - September (spring/summer) precipitation (mm) for CS2Met
600
500
400
300
200
100
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
0
year
W1 Precipitation (Climate Scenarios)
Total precipitation
(mm)
W8
W8
3500
3000
2500
2000
1500
1000
500
0
winter
W1
W1
W1
summer
total
Seasonal Period
Dry Year
Dry Spring
Wet Year
Choate, J. “Combined impacts of harvesting and climate variability on summer flow for snow and rain dominated
catchments in the Pacific Northwest”, MSc Thesis, San Diego State University
Wet Spring
Paired catchment experiments show long term reductions in
August flow (associated with changes in riparian zone
species) - Model results show similar reductions that are
potentially even greater under altered climate scenarios.
Do patterns of evapotranspiration-climate relationships
follow a similar spatial structure?
Is this structure the same as that of snow which also follows
topographic gradients?
Topography: redistribution of soil moisture; timing of
recharge (snowmelt), air-temperature/vpd, radiation (slope,
aspect)
Case Study: RHESSysbased eco-hydrologic
modelling:
Yosemite/Merced River
Basin (see Christensen
et a Poster)
600
550
550
-2
Annual Transpiration (mm m )
600
500
450
400
350
300
500
450
400
350
300
250
0
500
1000
Snowdepth (mm)
250
1500
17
0.8
0.75
CV Annual Transpiration
Annual Transpiration (mm m-2)
Basin Scale Transpiration-Climate Relationships
0.7
0.65
0.6
0.55
0.5
0
300
600
900
1200
Peak Snowdepth (mm)
1500
18
19
20
GSmeanT (C)
21
22
Spatial variation in annual transpiration - by elevation
Can spatial differences in
biomass (LAI) account for
these patterns - partial
So examine correlations with annual temperature,
precpitation, snow and other indices by elevation
Hig
h
elev
atio
ns
Change in Transpiration
(warm year - cold year)
High sensitivity
to temperature
Small
sensitivity
to climate
indicators
Mid
dle
elev
a
tion
s
Change in Transpiration
(high - average precip year)
c
d
elev
atio
Low
-347
0
Sensitivity to
water stress
ns
Change in Transpiration
(low - average precip year)
Sensitivity to
Temperature
+170
Small
sensitivity
to climate
indicators
Change in transpiration
Framework for assessing spatial structure of
summer streamflow and its sensitivity to climate
change and variability
Spatial patterns of current summer streamflow and response to climate variation and change
Process influence on summer flow
Landscape Controls
Modelling Issues
Drainage Efficiency
Discrete Geologic Classes
(High vs Western Cascade),
more spatially heterogeneous
geologically defined units in Sierras
MODEL: hydrologic parameters
assigned based on geo-classes
Recharge
Gradient of topographic (aspect, elevation)
control on snow
accumulation and melt,
and precipitation
MODEL: relevant scale at which
spatial variation in
snow accumulation and melt
must be defined
Evapotranspiration
Topographic differences
in vegetation water use
MODEL: stochastic disturbance regimes
(fire:where, how much, how frequently)
bgc- responses to climate
Disturbance Regimes
BIomass and Species Distributions
geology
topography
Conclusions for a work in
progress:
Geology matters
Topography matters for
vegetation water use
response but with a spatial
structure that is likely different
from that of snow
Next?
Systematic analysis that
considers the intersection of
the different characteristic
spatial scales of geo-ecosnow
US Geological survey
Measurement strategies that
link with model-based
hypothesis