Streamflow response to climate
warming in mountain regions:
Integrating the
effects of snowpack and
groundwater dynamics
Gordon E. Grant
USDA Forest Service
PNW Research Station
Christina Tague
University of California – Santa Barbara
Sarah Lewis
Oregon State University
Historic linear trends in April 1 Snow Water Equivalent
a. Observed
1950-2000
b. Modeled
Snowpacks have
gotten smaller, are
melting earlier…
Mote et al., 2005
…and are projected to
continue to diminish.
Montana
Washington
Idaho
Oregon
Red = rain instead of snow
in the winter
“At-risk” snow in a warmer climate:
22%
12%
61%
<3%
Oregon Cascades
Washington Cascades
Olympic Range
Pacific Northwest study area
Nolin and Daly (2006)
Historical Trends from Cascade Streams
Temporal centroid of hydrograph
Autumn minimum discharge
100
Temporal
Centroid (Tc)
Between 1948 and 2006:
Temporal centroid - 14 days earlier
Autumn minimum discharge - 1.4 cms lower
3
Discharge (m /s)
150
50
0
10/1/01
12/1/01
2/1/02
4/1/02
6/1/02
8/1/02
10/1/02
Jefferson (2006)
But….
• It’s not just about snow….
• Location (geology) matters too…
• Major implications for where, when, and
how much water will be available in the
future – and what its quality will be.
High Cascades
Western Cascades
(surface flow)
Western Cascades
Will
a me
tte R
iver
Cl
ac
ka
m
Precipitation and snowmelt
run off hillslopes directly
and rapidly to stream
channels.
as
N. Santiam
S.Santiam
High Cascades
(spring-fed)
McKenzie
Precipitation
infiltrates into young
lava flows and
emerges much later at
large springs.
2
Unit Discharge (cms/km )
12
9
6
3
0
10/1
12/1
2/1
4/1
6/1
8/1
Tague & Grant, 2009
Simple Conceptual Model - Linear Reservoir
Qt – streamflow at time t (in days)
Qo – streamflow at beginning of
recession
k – baseflow recession constant
Q(t ) = Qo e
( − kt )
(Tague & Grant, 2009)
pk15-day
k
tr
Treating recharge as a
single event,
we develop a model for
summer baseflow:
−k (t r )
r
l 5−day
Q = pk
e
Qr – summer streamflow
k - drainage efficiency
tr - days between snowmelt (tpk) and time of interest (tsummer)
pk15-day- snowmelt input (peak reduction in a watershed areal
mean of a 15 day running average
(Tague & Grant, 2009)
Summer flow sensitivity to changes in
snowmelt dynamics (first derivatives)
∂Qr
− k (t r )
Magnitude
=e
(pk15-day) ∂ pk15day
(
Timing
(tr)
)
∂Qr
−k (t
= pk15day ∗ ke
∂ (t r )
r
)
Both contain
k, drainage
efficiency
(Tague & Grant, 2009)
Magnitude
sensitive
unit change in daily streamflow (mm/day)
long
short
Not sensitive
deep/slow
shallow/fast
(Tague & Grant, 2009)
Timing
sensitive
unit change in daily streamflow (mm/day)
long
short
Not sensitive
deep/slow
shallow/fast
(Tague & Grant, 2009)
RHESSys
Original
framework
Added deep groundwater component
10
Mean unit discharge (mm/day)
8
A. High Cascade
wetter
winters
(920-2035m)
6
4
earlier and lower
snowmelt peak
2
0
Jan
decreased
summer flow
Feb Mar Apr May
Jun
Jul
Aug Sep Oct
Nov
Dec
Modeling scenarios: current climate; 1.5 C/1.5 C warming
14
12
10
B. Western Cascade
wetter
winters
(410-1630m)
8
6
4
2
0
Jan
minimal
snowmelt
Feb Mar Apr May
earlier summer
drought
Jun
Jul
Aug Sep Oct
Nov
Dec
Tague & Grant, 2009
geology
topography
Oregon Cascades
Young volcanic rocks =
Large groundwater system
Water stored in:
• groundwater
• snowpacks
• reservoirs
Sierra Nevada
Old granitic rocks =
Surface-flow dominated
Water stored in:
• snowpacks
• reservoirs
US Geological survey
California Sierras
Oregon Cascades
MC
LOC
McKenzie at
Clear Lake
MC
Lookout
Creek
Sagehen
Creek
LOC
Upper Merced
River
SAGE
YOS
SAGE
YOS
D
eep
G
roundw
ater
D
om
inate
Faster
S
halow
S
ub-surfaceFlow
D
om
inated
d
MC
LOC
SAGE
YOS
Geology
High Cascade
Basalt
Western
Cascade Basalt
Sierra
Volcanic
Sierra
Granitic
Elevation (m)
920-2035
410-1630
1928-2653
1200-3997
Drainage area
(km2)
239
64
2.6
465
Mean annual
streamflow (cm)
168.6
175.7
45.3
67.4
MC
LOC
SAGE
YOS
Tague & Grant, 2009
Change in mean unit discharge (mm/day)
with 1.5°C climate warming
more water
little change
less water
Tague & Grant, 2009
Oregon
Hydrologic
Landscape
Classification
Oregon Hydrologic Landscapes Map from EPA,
Wigington in prep
Validation Basins
Metolius River
Clear Lake, High Cascade Geology
VsHMM/VsHTH: Very wet, summer seasonality, High bedrock perm,
Mountain/Transitional terrain, Moderate/High soil perm
Lookout Creek, Western Cascade Geology
VwLML : Very wet, fall or winter seasonality, Low bedrock perm,
Mountain terrain, Low soil perm
• Timing of
Recharge
climatic
• Magnitude of
Recharge
• Vegetation
• Drainage
intrinsic
Efficiency
anthropogenic
• Dams
Tague & Grant, 2009
Perspective 1: Sensitivity of streamflow to climate
change in mountain landscapes
involves convolution of projected
snowpack changes, underlying
drainage efficiency and vegetation.
Perspective 2: Sensitivity varies over time as well as
space; landscapes dominated by rapid
subsurface flow (eg. Western
Cascades) are insensitive in the late
summer, but quite sensitive in the
spring.
Paradox: With respect to late summer streamflow,
areas with extensive groundwater recharge
will still have the most water, but stand to
lose the most.
We are now at the point where we
can begin to map sensitivity at the
landscape scale
www.fsl.orst.edu/wpg