Development of a coupled soil erosion and large-scale hydrology modeling system

Dazhi Mao, Keith A. Cherkauer

Ag. & Biological EngineeringPurdue University

Dennis C. Flanagan

NSERL

Outline

Introduction Concerns in coupling processes Coupling scheme Preliminary single cell analysis Development afterwards Current status

Introduction

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) Macro-scale hydrologic model

The Variable Infiltration Capacity (VIC) model • Mosaic-type representation of soil

and vegetation• Infiltration curve to control spatial

variability in soil moisture and infiltration

• Improved representation of cold season processes

Erosion modelsUSLE, RUSLE, MUSLE• Based on field-scale

observations • Lumped approach

The WEPP model • Continuous process-based

model • Capable of estimating spatial

and temporal distribution of soil loss

Coupling possibilities 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 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

WEPPVIC

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Concerns Different scales

Spatial scales

Temporal scales

Different parameters WEPP

Soil texture, management options, slope profile, erodibility, friction factors, rainfall intensity, duration, peak runoff, etc.

VIC Soil parameters,

vegetation type, precipitation depth, runoff depth

WEPP disaggregated rainfall intensity

VIC sub-daily rainfall depth

field scale large scale

Approach

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

Hydrologic pass file

VIC model soil

Soil texture

WEPP integrated algorithms

Adjustment parameters

DEM processing

Slope profile

WEPP-HE code

Annual soil Erosion

Soil erosion probability in VIC cell

Preliminary coupling scheme

- iterated process

30 arc-sec DEM

Soil loss

- original input data

- data processingIterated for sampled slopes

- data for WEPP-HE - intermediate data

Dailyclimate forcing

Hourlyprecipitation

30m DEM

Slope profile

Soil &vegetation

Adjusted erodibility, friction factors, & random roughness

WEPP-HE Code

WEPP model

ArcGIS

Precipitation& runoff output

VIC

Preliminary single cell test

wat30arc_DEM

Value

High : 471

Low : 271

Minnesota

Watonwan watershed30 arc-second DEM

Selected VIC grid cellat 1/8 degree

wat30arc_DEM

Value

High : 471

Low : 271

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

Complex data extraction and processing steps

Coupled model under-predict soil loss and sediment yield due to under-

estimation of hydrology parameters Difference in rainfall disaggregation

WEPP-breakpoint VIC-uniformly distributed by hours of

duration

Soil loss (kg/m2) Sediment Yield (t/ha)WEPP model 0.14 1.481Coupled model 0.054 0.576

Adjustments needed

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

- iterated process

30 arc-sec DEM

Soil loss

- original input data

- data processingIterated for sampled slopes

- data for WEPP-HE - intermediate data

Hourly precipitation

30m slope

Slope profile

Soil &vegetation

WEPP-HE Code

Extracted WEPP modelSource code

Generate adjustment parameters

ArcGIS

Precipitation& runoff output

VIC

WEPP disaggregated precipitation CLIGEN

Current development Rainfall disaggregation

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 Soil adjustment code

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 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

Rescale issue, validation Erosion estimation under different vegetation

cover/land-use Statistical analysis of results, distribution fit,

etc.

Thank you

Questions? Suggestions?