Evaluation of NDVI index for drought monitoring, using remote sensing technique (Case study: Isfahan Province)

The study of drought has important significance in water resources studies. Meteorological drought indices that are calculated directly based on meteorological data, such as rainfall, In the absence of such data, will not be useful in monitoring drought. The remote sensing techniques can be considered a useful tool in monitoring drought. In this research, using MODIS sensor data, Normalized Difference Vegetation Index Change during the years 2000 to 2008 were reviewed. In addition to vegetation, NDVI index can also be effective for drought monitoring, especially for dry farming.Considering this indicator, the vegetation cover was classified into 4 groups and areas were calculated for each class. Finally, SPI and NDVI were compared. The result of calculation of SPI shows severe droughts in 2008 and moderate drought in 2000 and 2008, respectively. NDVI index in the three years indicated that the poor vegetation cover is significantly increased. High level Pearson correlations (.704) observed between SPI and NDVI in significant level of 0.01. However, the results of the effect of precipitation on NDVI index showed, there is no simultaneous occurrence of meteorological and agriculture droughts for all year. For 2006, despite the fact that precipitation was higher than average rainfall, but in this year, agricultural drought (reducing the value of the index (NDVI) occurred. Conversely, in 2002 and 2004, which precipitation less than 2006, but dry farming and pasture conditions were better than in 2006. And also in 2003 by a margin of 2 mm in precipitation than 2002, NDVI index value dropped too much. The results emphasize on the definition of the index that show all of this issue.