high and dry: declining precipitation in the mountains of the pacific northwest charles luce us...
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High and Dry: Declining Precipitation in the Mountains of the Pacific Northwest
Charles Luce US Forest Service Research. Boise, ID
John Abatzoglou University of Idaho
Zachary Holden US Forest Service R1, Missoula, MT
Fu et al., 2010
Luce and Holden, 2009
Clark , 2010
Declining PNW Streamflows
-47.3 % to -38.7 %-38.7 % to -30.1 %-30.1 % to -21.5 %-21.5 % to -12.9 %-12.9 % to -4.3 %-4.3 % to 4.3 %
Not Significant at 0.1
Significant at 0.1
Luce and Holden, 2009
Two Kinds of ‘Trends’
Change in Mean Change in
VariabilityOrExtremes
1950 1960 1970 1980 1990 2000
20
03
00
40
05
00
60
07
00
80
0
BOISE R NR TWIN SPRINGS IDA
nn
ua
l Flo
w (
mm
)Middle Fork Boise – Trend in Water Yield Quantiles
75th %ile
50th %ile
25th %ile
Luce and Holden, 2009
25th %ile
a)
50th %ile
b)
75th %ile
c)
Mean
d)
-47.3 % to -38.7 %-38.7 % to -30.1 %-30.1 % to -21.5 %-21.5 % to -12.9 %
-12.9 % to -4.3 %-4.3 % to 4.3 %4.3 % to 12.9 %12.9 % to 21.5 %
Not Signif icant at 0.1 Signif icant at 0.1
25th – Dry Years 75th – Wet Years
50th Mean Luce and Holden, 2009
-47.3 % to -38.7 %-38.7 % to -30.1 %-30.1 % to -21.5 %-21.5 % to -12.9 %-12.9 % to -4.3 %-4.3 % to 4.3 %
Not Significant at 0.1
Significant at 0.1
Change in 25th %ile annual flowLuce and Holden, 2009
Why? E P
-41.8 % to -34.1 %
-34.1 % to -26.4 %
-26.4 % to -18.7 %
-18.7 % to -11.1 %
-11.1 % to -3.4 %
-3.4 % to 4.3 %
4.3 % to 12 %
12 % to 19.6 %
19.6 % to 27.3 %
27.3 % to 35 %
Trends in HCN2 Precipitation (% change in 25th %ile)
Energy Balance of a Surface
Net IncomingRadiation
Heat Lost throughEvaporation
TemperatureChange= +
0 1000 2000 3000 4000
-2.0
-1.5
-1.0
-0.5
0.0
Average Annual Runoff (mm)
Cha
nge
in 2
5th
%ile
Run
off (
mm
/day
)
52.3
39.2
26.2
13.1
0
Ene
rgy
Req
uire
men
t to
Eva
pora
te W
m2
1.8 W/m2
4.2 W/m2
Insufficient Additional Energy Available to Evaporate Water
-124 -122 -120 -118 -116 -114
01
00
02
00
03
00
0
Longitude
Ele
v (m
)
PrecipitationGage
WatershedMaxMeanMin
Kirshbaum and Smith, 2008
Orographic Precipitation
Precipitation Correlation with Regional Westerly Wind Speed
HCN StationSnotel Station
Precipitation Correlation with Regional Westerly Wind Speed
Nov-Mar Westerly Winds42.5-47.5 N, 115-130 W
ChangedWind
ChangedPrecipitation
Changed Streamflow
The Story So Far …
Why did the wind slow?
1950 1960 1970 1980 1990 2000 2010
7.0
7.5
8.0
8.5
9.0
9.5
10
.01
0.5
U7
00
mo
de
led
fro
m P
NA
, ME
I, a
nd
PD
O
Modeled WindspeedModeled TrendObserved Trend
U700=f(MEI,PNA,PDO), R2=0.37, P<0.001Influence of Climate Modes on Wind
1920 1940 1960 1980 2000
20
03
00
40
05
00
60
07
00
80
0
Year
MF
Bo
ise
Str
ea
mflo
w (
mm
)
2
1
0
-1
-2
PD
O
25th%ile StreamflowPDO
PDO
Lutz et al., 2012
Gedalof et al., 2004
Tree Ring Flow Reconstructions
Trends and Future Predictions
Why would warming slow the westerlies?
Future Changes in Pressure
Historical Trends in Nov-Mar 500hPa Height
Interannual Variations in Nov-Mar Westerlies
Future Wind Changes – from GCMs
20 of 24 models show a decline for the region studied!
Drivers of PPTN Change
• Dynamic– Spreading Hadley
Cell– Northward shift in
jetstream
– Changing winds over mountains
• Thermodynamic– Clausius-Clapeyron
Relationship
– Higher Lifting Condensation Level
– Cloud microphysics
See Seager et al., 2010; Smith and Kirnbaum, 2008
ChangedWind
ChangedMountain
Precipitation
Changed Streamflow
Changed Pressure
Distribution
Differential Heating
Cascading Changes
Is missing the effect of mountains on precipitation important?
Adaptation Choices
Regonda et al, 2005see also Mote et al, 2005
D April 1 SWE (cm)(1950-1999)- +
Historical April 1 Snowpack (SWE)
Sensitivity of April 1 SWE
Mote et al., 2005See also Mote, 2006
Fractional decrease in Apr 1 SWE with 3C warming
0 % to 10 %10 % to 20 %20 % to 30 %30 % to 40 %40 % to 50 %50 % to 60 %60 % to 70 %70 % to 80 %80 % to 90 %90 % to 100 %100 % to 100 %
Luce et al. (in review)
Loss in April 1 SWE with 3°C increase - SNOTEL
Stewart et al., 2004, 2005
100 150 200 250
Annual Streamflow (mm)
16 Mar
16 Apr
16 May
16 Jun
01 Apr
01 May
01 Jun
Ce
nte
r o
f Tim
ing
Salmon R nr Salmon
Luce and Holden, 2009
Annual Runoff Change (1980s->2090s, A1B)
IPCC AR4 SYR 3.5
Color where > 66% agreement in signStipled where > 90% agreement in sign
0
50
100
150
200
250
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Mon
thly
Wat
er Y
ield
(mill
ions
m3 )
1990s 2080s
MF Boise RiverModeled Differences 1990-2080
VIC Modeled Flow Changes
-120.00
-100.00
-80.00
-60.00
-40.00
-20.00
0.00
20.00
40.00
60.00
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Chan
ge in
Mon
thly
Yie
ld (m
illio
ns m
3 )
MF Boise RiverPredicted Change 1990-2080
VIC Modeled Flow Changes
-120.00
-100.00
-80.00
-60.00
-40.00
-20.00
0.00
20.00
40.00
60.00
Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Chan
ge in
Mon
thly
Yie
ld (m
illio
ns m
3 )
Modeled Flow Changes 1990s-2080s
Observed Flow Changes 1950s-1990s
Kormos, in prep
Kormos, in prep
Temperature Runoff Timing
Fire Extent
Burned Area Sensitivity
Westerling et al., 2006, 2011
Temperature
Precipitation
Runoff Timing
Fire Extent
AnnualRunoff
Burned Area Sensitivity
Holden et al., 2012
Temperature
Precipitation
Runoff Timing
Fire Extent
AnnualRunoff
Burned Area Sensitivity
r = 0.53
q = 0.17
q = 0.49
Holden et al., 2012
1972-2003 large forest firesFor years with early snowmeltWesterling et al, 2006
Fires on NationalForests2001-2007
1000 1500 2000 2500 3000 35000
.20
.40
.60
.81
.01
.21
.4Elevation (m)
Ap
r 1
SW
E P
reci
pita
tion
Se
nsi
tivity
(m
m/m
m)
1000 1500 2000 2500 3000 3500
0-1
00
-20
0-3
00
-40
0-5
00
Elevation (m)
Ap
r 1
SW
E T
em
pe
ratu
re S
en
sitiv
ity (
mm
/C)
Temperature Sensitivity Apr 1 SWE Precipitation Sensitivity Apr 1 SWE
Luce et al. (in review)
Summary• Mountain precipitation has declined in
Idaho.• ‘Low’ elevation precipitation has shown no
trend over the same period.• Knowledge of the trend is essential for
understanding historical snow and ecology changes and sensitivity.
• Insights from the trend may be informative for assessing future changes in precipitation.
