The document discusses the estimation of soil erosion using the Universal Soil Loss Equation (USLE) in ArcGIS Pro, developed by Wischmeier and Smith in the 1950s. It outlines the components of the equation (a = r * k * ls * c * p) and the sources of required data, including rainfall erosivity, soil erodibility, topography, crop management, and support practices. The document also highlights limitations of the model and provides links for further reference on various factors affecting soil erosion.

1. Soil Erosion
Estimation using
USLE Model in
ArcGIS Pro

2. Universal Soil Loss Equation (USLE)
• USLE was developed by Wischmeier and Smith in 1950s.
• USLE estimates the long-term average annual rate of erosion on a field slope based
on rainfall pattern, soil type, topography, crop system and management practices
(OMAFRA,2012).
• A= R * K * LS * C * P
• Where, A is the average annual soil loss (tons ha-1year-1),
R is the rainfall erosivity (MJmm ha-1 h-1 year-1),
K is the soil erodibility factor (tons ha-1 R unit-1),
LS is the topographic factor (dimensionless),
C is the cropping management factors (dimensionless),
P is the practice support factor (dimensionless)

3. Rainfall Erosivity (R)
• Rainfall erosivity is the kinetic energy of raindrop’s impact and the rate of associated
runoff.
• Data source: Global Rainfall Erosivity (https://esdac.jrc.ec.europa.eu/content/global-
rainfall-erosivity)
• Spatial coverage: World
• Pixel size: 30 arc-seconds (~ 1 km at the equator)
• Limitation: It can overestimate the soil erosion.

4. Soil Erodibility (K)
• Soil erodibility represents the effect of soil properties and soil profile characteristics
on soil loss.
• Data source: Harmonized World Soil Database v 1.2
(https://webarchive.iiasa.ac.at/Research/LUC/External-World-soil-database/HTML/)
• Spatial coverage: World
• Pixel size: 30 arc-seconds (~ 1 km at the equator)
• Limitation: It can overestimate the soil erosion.

5. Roose (1996)
Note that the table in the guide accounts
for % organic matter (OM), not just
organic carbon (OC). If we do not know
the conversion value for the area, the
value OC is multiplied by 1.72 to get OM.
OM=1.72*OC
The references for conversion factors are
given in IPCC-AFOLU report 2006.

6. Universal Soil Loss Equation (USLE)
• USLE was developed by Wischmeier and Smith in 1950s.
• USLE estimates the long-term average annual rate of erosion on a field slope based
on rainfall pattern, soil type, topography, crop system and management practices
(OMAFRA,2012).
• A= R * K * LS * C * P
• Where, A is the average annual soil loss (tons ha-1year-1),
R is the rainfall erosivity (MJmm ha-1 h year),
K is the soil erodibility factor (tons ha-1 R unit-1),
LS is the topographic factor (dimensionless),
C is the cropping management factors (dimensionless),
P is the practice support factor (dimensionless)

7. Topographic factor (LS)
• Topographic factors LS consist of slope length L and slope steepness S.
• Increase in the slope length L causes increase in erosion due to a progressive
accumulation of runoff in the direction of downslope.
• Increase in slope steepness factor S increase the soil erosion as a result of increasing
velocity.
L = [(FA * cell size)/22.13]m (Moore and Wilson, 1992)
• where, FA is flow accumulation, cell size is the size of DEM and m ranges from 0.2-0.6.
• S = [(sinβ * 0.01745)/0.09]n
• where, β is slope angle in percentage, n ranges from 1.0 -1.3.
• LS = (L * S)/100
• DEM data source: SRTM (30 m) (https://dwtkns.com/srtm30m/)

8. Formula to use in raster calculator
• Power((FA*30)/22.13,0.5)
• Power((Sin(slpe% *0.01745)/0.09,1.3)

9. Crop /vegetation and management factor (C)
• Used to determine the relative effectiveness of soil and crop management systems in
preventing soil loss.
• Value can be assigned for different landcover classes from look-up table in literatures.
• Landcover data source: Sentinel-2 Land Use/Land Cover (10 m)
(https://www.arcgis.com/apps/instant/media/index.html?appid=fc92d38533d440078f1
7678ebc20e8e2)
Support practice factor (P)
• It reflects the effects of practices that will reduce the amount and rate of the water
runoff and thus reduce the amount of erosion.
• Values are obtained from literatures based on the farmers practices.
• For easy interpretation, we can used 1 irrespective of landcover classes.

10. • ESRI 2020 LULC map with 10 classes
LULC class
number
Class name C value
1 Water 0
2 Trees 0.025
3 Grass 0.02
4 Flooded
Vegetation
1
5 Crops 0.05
6 Shrubs 0.4
7 Built Area 1
8 Bare ground 1
9 Snow/Ice 0
10 Clouds 0
Several references on estimating these factors can be
found online:
• USLE Fact Sheet
http://www.omafra.gov.on.ca/english/engineer/fa
cts/12-051.htm
• U.N. Food and Agriculture Organization
http://www.fao.org/docrep/T1765E/t1765e0c.htm
• RUSLE handbook (Renard et al., 1997)

11. Classification threshold might vary with countries

12. Recommendations
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•
•

13. • Supporting links:
• https://www.researchgate.net/publication/322371635_Integrated_universal_soil_loss_
equation_USLE_and_Geographical_Information_System_GIS_for_soil_erosion_estim
ation_in_A_Sap_basin_Central_Vietnam
• https://www.researchgate.net/publication/325402279_Estimation_of_Slope_Length_fa
ctor_L_and_Slope_Steepness_Factor_S_of_RUSLE_equation_in_the_Euphrates_River
_Watershed_by_GIS