Fatehi, Ahmad 
   
  
   
high neg change 
Meg change ^i 
Mo change 7 
Fos. change 
High pos. change 
  
  
zi) 
Figure 5: Sliced map of difference of NDVI values in 1991 and 1990 (NDVI1991-NDVI1990) Red=highly 
decreased NDVI values in 1991, yellow=decreased NDVI values in 1991, white=no change NDVI values in 1991, 
blue-increased NDVI value in 1991. 
  
8 Results 
Normalised Difference Vegetation Index (NDVI) data obtained from the Advanced Very High Resolution 
Radiometer (AVHRR) on board NOAA-11 were analysed to assess the changes of vegetation cover in south and 
southwest Iran. 
As the results of the analysis of the meteorological data show (Jalali et al 1999), there was no significant change 
on rainfall and temperature in 1990 and 1991. The NDVI profiles which, produced for many points in 1989 to 
1993 shows a high reduction in NDVI values in some parts in 1991. 
The exploratory Box plot (figure 3) of the NDVI values for the sample points shows the NDVI values in 
different years (1989 to 1993). It is clear that NDVI values of 1991 were lower than in the others years, 
especially when compared with 1990. The statistical analysis and t-test carried out on the NDVI values in 
different years show that the reduction of NDVI values in 1991 was significant. This reduction of NDVI values 
in 1991 take place stretching from the top of the Zagros mountain ridge towards the area near the source of the 
pollution. 
A relation between NDVI values and distance from the source of the pollution was established. The scatter plot 
of these values shows some differences between the two graphs drawn for the two years 1990 and 1991 (figure 
4). The gradient of best fit line is steeper in 1991 (from source of the pollution towards the mountain) because 
the NDVI values near the source of the pollution decreased much while far from the Persian Gulf towards the 
mountain area, these differences are low. The relation between NDVI and distance from the source of the 
pollution in the same vegetation cover type explains the decrease in NDVI values near the source of pollution in 
1991 as compared with 1990 (figure 4). To determine whether there are significant changes between the two 
sets of values the t-test was applied on the NDVI values. The result of this test shows a significant decrease of 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 431