Orographic Enhancement, declining
streamflow distributions and recent wildfire
activity in the Pacific Northwest US
Zachary A. Holden
Charles Luce
John Abatzoglou
Penny Morgan
Michael Crimmins
USDA Forest Service, Missoula
USDA Forest Service, Boise
University of Idaho, Moscow
University of Idaho, Moscow
University of Arizona, Tucson
Western US forest wildfires (1984-2010)
Monthly 800m climatic water balance data from PRISM (1895-2010)
1948-2010 average August defict
INPUTS
monthly data
(Tmin, Tmax, Prcp,
Dewpoint)
Radiation (r.sun)
Wind (NARR)
AWC (STATSGO)
1895-2010
OUTPUTS
Monthly Products:
PET
AET
Deficit
Dobrowski et al. (2013). Climate velocity of the coterminous US in the 20th century.
Terrain influences on water balance deficits
In dry years, largest departures
from average at high elevations
Topographic influences on
moisture diminish in driest years.
Each point = 1 year
Fire Frequency and Burned Area Sensitivity
• Trends in recent fire activity widely attributed to
warming temperatures
• Warm spring temperatures decrease snow
accumulation /accelerate melt
• Early melt would accelerate homogenization of
landscape moisture
Fire
Extent
Temperature
Runoff
Timing
Westerling et al., 2006, 2011
Streamflow Timing
Stewart et al., 2005
Trends in HCN2 Precipitation (% change in 25th %ile)
27.3 % to 35 %
19.6 % to 27.3 %
12 % to 19.6 %
4.3 % to 12 %
-3.4 % to 4.3 %
-11.1 % to -3.4 %
-18.7 % to -11.1 %
-26.4 % to -18.7 %
-34.1 % to -26.4 %
-41.8 % to -34.1 %
700
400
500
600
75th %ile
50th %ile
200
300
Annual Flow (mm)
800
R Trend
NR TWIN
SPRINGS
Middle ForkBOISE
Boise –
in Water
YieldIDQuantiles
25th %ile
P.25=0.02
1950
Luce and Holden, 2009
1960
1970
1980
1990
2000
76% of stream gages show statistically significant trends in dry years
Large magnitude changes in annual flow in drier years
> 40% decreases in runoff at some gages
Significant at
Not Significant at
0.1
0.1
-4.3 % to 4.3 %
-12.9 % to -4.3 %
-21.5 % to -12.9 %
-30.1 % to -21.5 %
-38.7 % to -30.1 %
-47.3 % to -38.7 %
Streamflow timing and distribution are fundamentally related
Smaller snowpacks melt faster
Interactions between water volume and radiation
Influence date of 50th percentile flow
Empirical relationship between timing/flow
16 Jun
Theoretical curves
Center of Timing
01 Jun
16 May
01 May
16 Apr
Salmon R nr Salmon
01 Apr
Luce and Holden, 2009
16 Mar
100
150
200
250
Moore (2007)
Annual Streamflow (mm)
Wildfire annual area burned from MTBS data (1984-2006)
Environmental Site Potential (ESP) from LANDFIRE
Holden, Luce, Crimmins and Morgan (2011)
Analysis of Streamflow-Wildfire Area Burned Relationships
PCA on annual flow and date of 50th percentile flow from 84 Stream Gages in the PNW
3 PC’s on Annual flow explain 90% of the total variation across all gages.
Multiple regression models with streamflow metrics as predictors of annual wildfire
area burned
Model
Area Burned
Area Burned
Area Burned
Area Burned
Area Burned
Area Burned
~ PC1F+PC2F*PC3F + PC1T
~ PC1F+PC2F*PC3F
~ PC1F+PC2F+PC3F
~ PC1F+PC2F
~ PC1T
~ PC1F
Holden, Luce, Crimmins and Morgan (2011)
ΔAIC
0.0
0.7
4.2
5.0
7.2
7.2
R2 (adj)
0.471
0.466
0.35
0.28
0.24
0.18
p-value
0.004
0.004
0.016
0.01
0.02
0.03
Burned Area Sensitivity
Fire Extent
Temperature
Runoff
Timing
Westerling et al., 2006, 2011
Burned Area Sensitivity considering influence of
precipitation on melt and flow timing
• Snowpack and resulting annual flow have a direct, mechanistic influence on
Timing (more water = delayed timing)
• Timing has no influence on annual discharge
Precipitation
Annual
Runoff
Fire Extent
Temperature
Runoff
Timing
Path analysis
Application of multiple regression that seeks to identify causality in sets of
correlated variables
Remove spurious influence of annual flow on flow timing
amount of water may provide simpler mechanistic predictor of fire activity
than timing
Precipitation
Annual
Runoff
q = 0.49
Fire Extent
r = 0.53
Temperature
Runoff
Timing
r = standardized regression coeff.
q = correlation after removing spurious correlation
q = 0.17
Holden et al., 2011
Where is the missing water?
Warmer temperatures increase evapotranspiration?
Decreased high elevation precipitation?
Orographic Precipitation
Zonal Wind Flow
west
Adiabatic cooling
condensation
Adiabatic compression
warm, dry air mass
Foehn wind
east
10
le
9
75 th%i
median
8
mean
7
700 hPa Zonal Wind Speed (m/s)
11
NCEP Nov.-March zonal wind speeds (1948-2012)
25 th%
ile
1950
1960
Luce et al. (2013)
1970
1980
1990
2000
2010
Zonal Wind and Precipitation:
Differential correlation
with elevation
Correlation of 1979-2012 NovMar HCN (circles) and SNOTEL
(squares) precipitation with NovMar 700 hPa zonal winds over
42.5-47.5° N and 110-130° W
(u700).
Hypothesis:
Slower westerlies have decreased
orographic enhancement and
reduced high elevation precipitation
May be responsible for observed
decreases in annual flow
Luce et al. (2013)
Conclusions
Streamflow observations provide an integrated measure
of all water in a basin
Annual winter precipitation is strongly correlated with
westerly winds at higher elevations
significant decreasing trends in westerly winds
Decreased orographic enhancement associated with
slower westerlies may explain declining streamflows
suggests an alternative mechanism by which regional-scale
climatic change has influenced fire activity in the region.
Managing wildfires in complex terrain
TOPOFIRE: Interactive web server for monitoring terrain and insectinduced effects on fire danger (NASA Wildland Fire Applications)
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Daily FASST runs generated each day at 240m
Ground surface temperature (Min, Max)
Soil moisture (5cm, 50cm)
Account for all terrain-varying energy inputs
(solar radiation, wind, temperature, humidity)
Acknowledgements
FUNDING
NASA A.35 Wildland Fire Applications
NSF – EPSCOR
USFS Region 1
Many great collaborators
Russ Parsons, Matt Jolly, Solomon Dobrowski,
Marco Maneta, Susan Frankenstein, Erin Landguth,
Anna Klene, Rob Keefe