Sciences in Cold and Arid Regions ›› 2022, Vol. 14 ›› Issue (1): 32-42.doi: 10.3724/SP.J.1226.2022.21003.

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Desertification status mapping in Muttuma Watershed by using Random Forest Model

S. Dharumarajan1(),Thomas F. A. Bishop2   

  1. 1.ICAR-National Bureau of Soil Survey and Land Use Planning, Regional Centre, Hebbal, Bangalor 560024, India
    2.Faculty of Agriculture and Environment, The University of Sydney, Sydney, NSW 2006, Australia
  • Received:2021-01-08 Accepted:2021-10-11 Online:2022-02-28 Published:2022-03-03
  • Contact: S. Dharumarajan


Potential of the Random Forest Model on mapping of different desertification processes was studied in Muttuma watershed of mid-Murrumbidgee river region of New South Wales, Australia. Desertification vulnerability index was developed using climate, terrain, vegetation, soil and land quality indices to identify environmentally sensitive areas for desertification. Random Forest Model (RFM) was used to predict the different desertification processes such as soil erosion, salinization and waterlogging in the watershed and the information needed to train classification algorithms was obtained from satellite imagery interpretation and ground truth data. Climatic factors (evaporation, rainfall, temperature), terrain factors (aspect, slope, slope length, steepness, and wetness index), soil properties (pH, organic carbon, clay and sand content) and vulnerability indices were used as an explanatory variable. Classification accuracy and kappa index were calculated for training and testing datasets. We recorded an overall accuracy rate of 87.7% and 72.1% for training and testing sites, respectively. We found larger discrepancies between overall accuracy rate and kappa index for testing datasets (72.2% and 27.5%, respectively) suggesting that all the classes are not predicted well. The prediction of soil erosion and no desertification process was good and poor for salinization and water-logging process. Overall, the results observed give a new idea of using the knowledge of desertification process in training areas that can be used to predict the desertification processes at unvisited areas.

Key words: desertification processes, vulnerability indices, Random Forest Model, extrapolation

Figure 1

Location of (a) the study area in Australia (b) Muttuma Watershed"

Table 1

Assigned scores of soil quality indices for calculation of DVI"

Soil depthDrainage
Deep >100 cm1.0Well drained1.0
Moderate 50-1001.5Imperfectly drained1.5
Shallow <502.0Poorly drained2.0
Soil forming processesRunoff
Alluvial1.0Soil Quality Indices
Soil textureGood1.00-1.33
Coarse loamy, fine-loamy1.0Moderate1.33-1.66
Fine, very fine1.5Poor1.66-2.00
Organic Carbon

Table 2

Assigned scores of terrain parameters for calculation of DVI"

NE, NW1.13-81.33
SE, SW1.9

Table 3

Assigned scores of vegetation quality parameters"

Fire riskPlant cover
Annual crops, modified grazing lands1.00High (>40%)1.00
Permanent grasslands, perennial pastures, perennial horticulture1.50Moderate (10%-40%)1.80
Woodlands, native forest2.00Low (<10%)2.00
Erosion protectionScoreResistance to droughtScore
Woodlands, native forest1.00Woodlands, native forest1.00
Permanent grassland, perennial pastures, perennial horticulture1.33Permanent grassland, perennial pastures, perennial horticulture1.33
Intensive animal husbandry, modified grazing lands1.66Intensive animal husbandry, modified grazing lands, Annual crops associated with permanent crops1.66
Dryland annual crops, non irrigated arable land2.00Dry land annual crops2.00

Table 4

Assigned scores of land utilization index"

Land useScoreLCCScore
Annual crops, modified grazing lands1.0I&II2.00
Permanent grasslands, perennial pastures, perennial horticulture1.5III&IV1.50
Woodlands, native forest2.0>V1.00

Table 5

Description of desertification vulnerability indices classes"

DVI classRangeDescription
Nil to slight1.00 ≤ DVI < 1.25Slight or non-threatened areas to desertification subjected to very low or no erosion with no or slight salinization risk
Potential1.25 ≤ DVI < 1.50Potential areas to desertification subjected to low to moderate erosion rates or low salinization risk
Fragile1.50 ≤ DVI < 1.75Fragile areas to desertification subjected to moderate to high erosion rates due to intensive cultivation or overgrazing or frequent fires; or subjected to moderate salinization risk
Critical1.75 ≤ DVI ≤ 2.00Critical areas to desertification and subjected to very high erosion rates due to intensive cultivation, overgrazing, frequent fires; or subject to high or very high salinization risk

Table 6

Datasets used for model building"

PredictorSourceSpatial resolutionTypeRange
Temperature (max)Bureau of Meteorology-Q19.7-22.8
Rainfall (mm)Bureau of Meteorology-Q556-739
Evaporation (mm)Bureau of Meteorology-Q1,424-1,557
SlopeASTER GDEM30 mQ0.0-0.45
AspectASTER GDEM30 mQ0.0-6.28
LS factorASTER GDEM30 mQ0.0-9.39
Wetness indexASTER GDEM30 mQ4.4-24.9
Sand 0%-30% (cm)Soil map grid of Australia3 secQ30.7-63.9
pH (0%-30 (cm))4.4-5.7
Clay (0%-30% (cm))10.3-44.2
Sand (60%-100% (cm))Soil map grid of Australia3 secQ6.5-44.5
pH (60%-100% (cm))3.6-5.5
Clay (60%-100% (cm))2.5-35.1
Organic carbonSoil map grid of Australia3 secQ0.49-1.91
NDVIMOD13Q1 (2000-2015)250 m, 16 daysQ0.34-0.67
EVIMOD13Q1 (2000-2015)250 m, 16 daysQ0.19-0.44
Vulnerability indicesClimatic quality index-C-
Terrain quality Index-C-
Vegetation quality index--
Land Utilization Index-C-
Soil Quality index-C-

Figure 2

Training areas for desertification prediction"

Figure 3

Desertification vulnerability index map"

Table 7

Confusion matrix for training (pixels) and testing (pixels)"

ClassTraining dataTesting data
Erosion (E)1,337347311,8144,68683,723418,458
Waterlogging (WL)1212138435576934666488
No desertification (ND)150264,50864,6907,62421728,45862836,927
Salinization (S)23545611510219763263

Figure 4

Predicted desertification map"

Figure 5

Random forest importance of covariates on desertification processes"

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