Drought Monitoring Using Vegetation Index (NDVI) (Case study: Rangelands of Ilam Province)

To identify an appropriate index for monitoring and evaluation of drought, rainfall data obtained from meteorological stations of Ilam Province from 2000 to 2011 and MODIS satellite images with 16-day intervals were collected and processed. The Standardized Precipitation Index (SPI) was calculated based on rainfall data; therefore, the rainfall data were used for measuring SPI and satellite images were used for calculating NDVI. Also, the percentages of canopy cover in range types were selected from the information of the National Evaluation of rangelands in different climatic zones. The correlation between SPI and NDVI and also canopy cover and NDVI was examined. The relationship between vegetation index (NDVI) and SPI was determined by regression. The results of SPI showed that in 2000 a severe drought and in 2006 a medium wet occurred in rangelands of Ilam Province. NDVI value variations have as well confirmed it. The results showed that NDVI and life form (annual forb and annual grass) has the highest percentage of correlation. Also examining of result showed that most correlation of SPI and NDVI was in 3 and 6-months intervals. Evaluation of regression models performance in range types described that models in 3 and 6- months intervals was suitable for monitoring drought. The result of regression confirmed that NDVI was an appropriate index for monitoring and assessment of drought.