In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Voi. XXXVIII, Part 7B 
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Figure 3. Vegetation changes detected by SAVI2 and NDVI 
Among all other indices, only SAVI2 showed a reduction in the 
fraction of vegetation. The rest of the indices were also returned 
mixed pixels. 
Next, the drought assessment was examined using three indices: 
VSWI, PDI and MPDI. As table 1 reveals in 2002, annual 
rainfall increased sharply. The results of PDI approved that the 
drought severity decreased. Since the PDI is based on soil 
moisture and the reflectance of the targets in the Red and NIR 
bands, it is suitable for meteorological drought monitoring. 
On the other hand, the results of VSWI, also, showed mixed 
pixels. This is due to the fact that this index is based on the 
NDVI (Carlson 1994) and as mentioned before, NDVI is not 
appropriate for arid areas. 
Ghulam et al, in 2007 used the NDVI to assess drought using 
MPDI, but as the result showed, this index is not very 
appropriate for arid areas. Consequently, we examined its 
substitution with another index. Among all studied indices only 
SAVI2 had well presented the vegetation fraction (F v ). 
Therefore, the fraction of vegetation has been estimated using 
the following index. 
SAV12-SAVI2 Max 
V ~ [ SAVI2 m -SAVl2 M J 
(5) 
The results of the revised MPDI indicated that the area with 
higher drought severity (more than 0.4) has largely increased 
(Figure 4). The regions with moderate drought severity were 
located in the northern and eastern hillside. These regions, 
keeps the moisture for a longer time. Therefore, the intensity of 
drought is lower than the other hillsides especially in 
comparison with the southern hillsides. The lowest values for 
the revised MPDI appeared in the high-land regions. In the 
high-land regions, there is snow until the end of the growing 
season and provide a supply of water for the vegetation growth. 
Figure 4. MPDI changes (1999-2002) 
Studying the meteorological data reveals that drought did not 
occurred in 2002 and the results of PDI confirmed that as well. 
However, the results of the revised MPDI showed that the 
drought severity has increased. Therefore, it can be concluded 
that both meteorological data and the indices based on the 
satellite images, are essential for an accurate assessment of 
drought disaster. 
In summary, this study had the following conclusions: 
1. NDVI is not an appropriate index for vegetation assessment 
in the arid areas. 
2. Vegetation indices which consider soil background 
reflectance such as SAVI2 can be more useful for vegetation 
assessment. 
3. The PDI is suitable for meteorological drought monitoring. 
4. Meteorological data and Remote sensing data are both 
essential for an accurate assessment of drought. 
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