International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
  
  
  
  
    
  
L4 Mroad shp 
2 rishp 
  
—— dO IO 
=a 
Figure 2: (a) Predicted soil losses from rain-fed fields 
for 1972. Black areas are masked out areas of basalt, 
built-up areas and rangeland areas. (b) Predicted soil 
losses from rangeland for the same year. Black areas 
are masked out built-up, basalt and cultivated areas. 
7x. / Mroad.shp 
© 
= 
5 
  
I" i S 
jo, 
c 
DO RON 
  
4 : / J^. / Mroad.shp 
I f 92 vf.shp 
— 1 
{ 2 
3 
92 nshp 
Figure 3: (a) Predicted soil losses from rain-fed fields 
for 1992. Black areas are masked out areas of basalt, 
built-up areas, rangelands and irrigated cropland. (b) 
Predicted soil losses from irrigated cropland in 1992. 
Black areas are masked out areas of basalt, built-up 
areas, rangelands and rain-fed fields. (c) Predicted soil 
losses from rangeland for the same year. Black areas 
are masked out built-up, basalt and cultivated areas. 
3.3 Verification of the Soil Loss Maps 
3.3.1 The Verification Data Set: It was not 
possible to validate the predicted soil loss maps for 
1972 and 1992 in the years for which the data was 
acquired. However, an attempt to verify the soil loss 
model was made by comparing the soil loss 
predictions for 1992 with evidence of soil loss from 
47 rain-fed fields at the end of the 1998/1999 wet 
season. The presence or absence of visual evidence of 
soil erosion in these fields was used to determine 
whether erosion had occurred or not during the 
preceding wet season. 
The method proposed by the FAO (1979) for the 
identification of soil erosion using post-erosion 
evidence was adopted. This method uses simple 
visual criteria (Plates 1, 2, 3 and 4). Furthermore, it 
has been found that the least ambiguous evidence of 
soil erosion by water in the fields was rilling (Plate 1). 
Therefore, most of the subsequent model verification 
relies on rilling as a surrogate for ‘observed soil loss’. 
  
Plate 1: Rills formation by the coalescence of two 
plough furrows. 
  
Plate 2: A trail of eroded sediment across a cracked 
silt-rich surface. 
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