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Predicting the hydrologic implications of land use change in forested catchments. Dennis P. Lettenmaier Department of Civil and Environmental Engineering University of Washington Chapman Conference on Ecosystem Interactions with Land Use Change June 14, 2003 Santa Fe, New Mexico. - PowerPoint PPT Presentation
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Predicting the hydrologic implications of land use change in forested catchments
Dennis P. LettenmaierDepartment of Civil and Environmental Engineering
University of Washington
Chapman Conference on
Ecosystem Interactions with Land Use Change
June 14, 2003
Santa Fe, New Mexico
Outline of this talk
• Background – the signature of land use change
• Example 1 – Logging and flooding in the Pacific Northwest
• Example 2 –Hydrologic effects of vegetation change in the upper Midwest
• Some outstanding issues in prediction of hydrologic effects of land cover change
1) Continental and regional signatures of land cover change
Source:
National Institute of Public Health and the Environment (RIVM, Netherlands) and the Center for Sustainability and the Global Environment (SAGE, University of Wisconsin).
Estimated 1850 and 1990 global land cover
Early Conifer
Middle Conifer
Late Conifer
Early Deciduous
Middle Deciduous
Late Deciduous
Brush
Agriculture
Water
Historical (1900) Current (1990)
Columbia River basin estimated 1900 and 1990 vegetation cover (from ICBEMP)
2) Example 1: Logging and flooding in the Pacific Northwest
Assessment approach – spatially distributed hydrologic modeling
Mechanisms for hydrologic change
• Rain-on-snow runoff generation
• Channel manipulation via forest roads
• Water table (hence saturated area changes) via altered evaporative demand
• Combinations of above
Investigation of forest canopy effects on snow accumulation and melt
Measurement of Canopy Processes via two 25 m2 weighing lysimeters (shown here) and additional lysimeters in an adjacent clear-cut.
Direct measurement of snow interception
SWE difference for February 1996ROS event; harvest - no harvest
More snow at beginning
of event
Less snow at end of
event
Simulated response to forest harvestSub-basins of the Deschutes River, WA
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
0.0 5.0 10.0 15.0 20.0
Increase in 2.3-Year Return Flood (%)
Incr
ease
in 1
0-Y
ear
Ret
urn
Flo
od (
%)
Sources of road-derived runoff
Surface routes for road runoff
Effect of forest roads on water table
Drier with roads
Wetter with roads
Simulated streamflow w/ and w/o forest roads
Hard Creek
Ware CreekHard Creek
Ware Creek
Bottom line:
• Both vegetation removal and roads contribute to increased peak runoff
• Effects more or less superimpose• For the Deschutes basin, each effect represents
about a 10% increase in the ~10 yr flood• Relative magnitude of vegetation effect decreases
with return period, road effect increases
Sediment Modeling with the DHSVM Watershed Sediment Module
DHSVM
MASS WASTING
SURFACE EROSION
CHANNELEROSION
Watershed Sediment Module
OUTPUT
Q
Qsed
Portraying Watershed Change Sediment Model
Wildfire in the Icicle Creek basin
Mass Wasting Module
MASS WASTING
Multiple realizations of total failure locations
Multiple time series of sediment supply
Soil depthDEM
Soil typeVegetation type
P(F
) Soil cohesionRoot cohesionVeg. SurchargeFriction angle
Surface Erosion ModuleMultiple time series of sediment supply
Overland flowSURFACE EROSION
Roads and streams
SoilPrecipitationVegetation
DEM
Distribution of sediment delivery
to channels(roads and streams)
Channel Erosion Module
CHANNELEROSION
Channel flow Mean and standard deviation of sediment
load for selected channel reaches
Distribution of sediment delivery
to channels(roads and streams)
0
1
23.9
21.9
17.1 18.0
19.8
19.219.7
18.9
19.5
19.3
23.9
21.9
17.1 18.0
19.8
19.219.7
18.9
19.5
19.3
Probability of slope failure before and after Fourth of July Fire
Icicle Creek Vegetation
Pre-fire
Post-fire
Approximate extent of August
2001 fire
3) Example 2 –Hydrologic effects of vegetation change in the upper
Midwest
Regional Land Use ChangePresettlement Land Use Modern Land Use
Land Use Changes:
Change in Forest Cover
Variable Infiltration Capacity (VIC) Macroscale Hydrologic Model
• Full Energy Balance• Full Water Balance• Mosaic Vegetation
Cover• Variable Infiltration
Curve Generates Runoff
• Arno Baseflow Curve
Evaporation Changes
Dif
fere
n ces
(m
m)
Eva
p ora
t ion
(m
m)
Presettlement Land Use Modern Land Use
Snow Cover Changes
Dif
fere
n ces
(m
m)
Snow
Wat
er
Equ
ival
ence
(m
m)
Presettlement Land Use Modern Land Use
Calibrated Flow Comparison
Chippewa River Flow
St. Croix River Flow
Flow Comparisons
Modern Land Use Pre-Settlement Land Use
0
20000
40000
60000
80000
100000
120000
Dis
cha
rge
(m
3/s
)
0 365 730 1095 1460 1825
Days Since 1951
0
10000
20000
30000
40000
50000
60000
Dis
cha
rge
(m
3/s
)
0 365 730 1095 1460 1825
Days since 1/1/1951
• Discharge was calibrated using:– Modern land use types
– Discharge Observations from 1980-1989
• Plots compare discharge for the first 5 simulation years (1951-1955)
• Discharge also generated for presettlement land use using the same parameters
Extreme Flow Comparison
• Annual peak and low flow events for Water Years 1951-1995
• Compares simulated flow with presettlement and modern land use
• Both peaks and low flows are greater with modern land use
Annual Low Flows
Annual Peak Flows
Peak and Low Flow Comparisons
St. Croix River Chippewa RiverWisconsin River Mississippi River
0
50
100
150
200
250
Mo
de
rn (
m3/s
)
0 50 100 150 200 250
Presettlement (m3/s)
500
1000
1500
2000
2500
Mo
de
rn (
m3 /
s)
500 1000 1500 2000 2500
Presettlement (m3/s)
Cumulative Flow Comparison
• Cumulative discharge from 1951 to 1995
• Decreased evaporation from smaller forested areas yields more runoff with modern land use
Chippewa River Cumulative Flow
St. Croix River Cumulative Flow
Cumulative Flow Comparisons
Modern Land Use Pre-Settlement Land Use
0
100000
200000
300000
400000
Dis
cha
rge
(km
3 /d
ay)
0 1825 3650 5475 7300 9125 10950 12775 14600 16425
Days Since 1950
0
50000
100000
150000
200000
Dis
cha
rge
(km
3 /d
ay)
0 1825 3650 5475 7300 9125 10950 12775 14600 16425
Days since 1/1/1950
4) Some outstanding issues in prediction of hydrologic effects of
land cover change
1. The calibration problem
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
4/1
/65
4/8
/65
4/1
5/6
5
4/2
2/6
5
4/2
9/6
5
5/6
/65
5/1
3/6
5
5/2
0/6
5
5/2
7/6
5
Flo
w (
cfs
)
0
10000
20000
30000
40000
50000
60000
70000
80000
900004
/1/6
9
4/8
/69
4/1
5/6
9
4/2
2/6
9
4/2
9/6
9
5/6
/69
5/1
3/6
9
5/2
0/6
9
5/2
7/6
9
Date
Flo
w (
cfs
)
Observed Modern Channel Modern Inflows
Presettlement Channel Modern Inflows Presettlement Channel Presettlement Inflows
1965 Flood Hydrograph (Flood of Record)
1969 Flood Hydrograph
Mississippi River at Anoka, MN
2. The model complexity problem
00.10.20.30.40.50.60.70.80.9
1
0 1 2 3 4 5 6 7 8 9 10
Years since wildfire
Effe
ctiv
e R
oot C
ohes
ion
Root decay Root regrowth Total root strength
Effect of wildfire on simulated root cohesion