Development of a coupled soil
erosion and large-scale hydrology
modeling system
Dazhi Mao, Keith A. Cherkauer
Ag. & Biological Engineering
Purdue University
Dennis C. Flanagan
NSERL
Outline
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Introduction
Concerns in coupling processes
Coupling scheme
Preliminary single cell analysis
Development afterwards
Current status
Introduction
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Soil erosion by water is a major concern for
resource management
Frozen soil modifies surface runoff
generation and erodibility of the soil
Large-scale hydrology model to represent the
impact of frozen soil on erosion at
management scale
Introduction (continued)
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Macro-scale hydrologic model
The Variable Infiltration Capacity
(VIC) model
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Mosaic-type representation of soil
and vegetation
Infiltration curve to control spatial
variability in soil moisture and
infiltration
Improved representation of cold
season processes
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Erosion models
USLE, RUSLE, MUSLE
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Based on field-scale
observations
Lumped approach
The WEPP model
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Continuous process-based
model
Capable of estimating spatial
and temporal distribution of soil
loss
Coupling possibilities
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The VIC model improved representation of cold season
processes (Cherkauer and Lettenmaier, 1999)
The stand-alone WEPP-Hillslope Erosion (WEPP-HE)
code (Flanagan et al. 2005) provide basis for coupling
with hydrology model
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Predicts soil loss for single storm event
Needs only soil texture, slope profile, adjusted daily erodibility and
friction factors, and hydrologic pass files
Use basic erosion algorithms from the WEPP model to
represent soil erosion in the VIC model
Concerns
Different scales
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Different parameters
 WEPP
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Spatial scales
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VIC
WEPP
field scale
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large scale
Temporal scales
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VIC
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0.16
0.14
Rainfall depth
1.2
Intensity
1
0.8
0.6
0.4
0.12
0.1
0.08
0.06
0.04
0.02
0.2
0
0
0
0.16 0.21 0.27 0.34 0.42 0.53 0.66 0.84 1.16 4.09
Time
WEPP disaggregated
rainfall intensity
1
3
5
7
9
11
13
15
17
19
Hour
VIC sub-daily
rainfall depth
21
23
Soil texture, management
options, slope profile,
erodibility, friction factors,
rainfall intensity, duration,
peak runoff, etc.
Soil parameters,
vegetation type,
precipitation depth, runoff
depth
Approach
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Downscale VIC model I/O to run WEPP-HE
code
Represent topographic variability
Statistical/stochastic presentation of output from
WEPP-HE in a VIC grid cell
Conceptual coupling scheme
VIC model output
DEM processing
Hydrologic pass file
Slope profile
WEPP-HE code
WEPP integrated
algorithms
VIC model soil
Soil texture
Annual soil
Erosion
Soil erosion probability in VIC cell
Adjustment
parameters
Preliminary coupling scheme
30 arc-sec
DEM
WEPP model
Daily
climate
forcing
30m DEM
Soil &
vegetation
ArcGIS
Hourly
precipitation
VIC
Precipitation
& runoff
output
- original input data
- intermediate data
- data for WEPP-HE
- data processing
- iterated process
Slope
profile
Adjusted erodibility,
friction factors, &
random roughness
WEPP-HE Code
Soil
loss
Iterated for sampled slopes
Preliminary single cell test
Watonwan watershed
30 arc-second DEM
Minnesota
wat30arc_DEM
wat30arc_DEM
Value
High : 471
Value
Low :High
271
: 471
Low : 271
Selected
VIC grid cell
at 1/8 degree
 Agricultural land use (corn, no-till)
 Nearest station climate file
 30m DEM
 Random sample 25 slopes (spatial analyst) for single cell test
evaluation
Preliminary results
Preliminary results
WEPP model
Coupled model
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Soil loss (kg/m2) Sediment Yield (t/ha)
0.14
1.481
0.054
0.576
Complex data extraction and
processing steps
Coupled model under-predict soil loss
and sediment yield due to underestimation of hydrology parameters
Difference in rainfall disaggregation
 WEPP-breakpoint
 VIC-uniformly distributed by hours of
duration
Adjustments needed
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Break down precipitation (daily-subdaily)
using WEPP code
Extract soil erodibility adjustment code from
WEPP model to remove the intermediate
process
Reinvestigate and solidify slope profile
rescale method
Develop soil loss probability distribution
Application in larger study area/multiple cells
Adjusted coupling scheme
WEPP disaggregated
precipitation
Hourly
precipitation
Soil &
vegetation
VIC
Precipitation
& runoff
output
- original input data
- intermediate data
- data for WEPP-HE
- data processing
- iterated process
30 arc-sec
DEM
CLIGEN
30m slope
Extracted
WEPP model
Source code
ArcGIS
Slope
profile
Generate
adjustment
parameters
WEPP-HE Code
Soil
loss
Iterated for sampled slopes
Current development
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Rainfall disaggregation
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Regrid study domain to create .PAR file for each
VIC grid cell based on existing CLIGEN PAR
stations (inverse distance)
Use CLIGEN to generate .CLI file for each cell
Extract disaggregation code from WEPP source
code to generate daily disaggregated storm
Integrate disaggregated rainfall into hourly
precipitation
Hourly precipitation and daily TMIN, TMAX, and
WIND are used to create VIC climate forcing files
Current development
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Soil adjustment code
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Extracted soil texture, friction, erodibility
adjustment codes from WEPP source code
Compiled to form a new Fortran program that
reads in VIC soil and climate input data and
output adjustment variables for each day
Still need to work
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Slope profile rescale
 Monofractal scaling method (Bowling et al,
2004) where fractal dimension is estimated
using variogram technique (Zhang et al. 1999;
Xu et al. 1993)
 The VIC grid cell is divided into subregions
(3x3 30arc) to maintain local fracal properties
The distribution of slope for the whole
watershed fits a Laplace distribution
30arc-DEM
30m slope
Improved result
Soil loss (kg/m2)
Sediment yield (t/ha)
Mean
Std
Mean
Std
WEPP
0.1007
0.0424
1.0384
0.4248
Coupled
model
0.0993
0.0479
0.9936
0.479
Average annual (1980-1990)
Still need to work
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Rescale issue, validation
Erosion estimation under different vegetation
cover/land-use
Statistical analysis of results, distribution fit,
etc.
Thank you
Questions?
Suggestions?