عنوان مقاله [English]
نویسنده [English]چکیده [English]
In order to define a surrogate index instead of climatic indices for analyzing and monitoring droughts, monthly rainfall data ( period of growth from March to September) of 36 stations spread over Esfahan and NOAA satellite images during the 1997- 2003 period were prepared and processed. The climatic index of SPI was computed from monthly rainfall and the Normalized Difference Vegetation Index (NDVI) was extracted from NOAA images. Based on land use map, the vegetation map of Esfahan Province were prepared that has rich, medium and poor range lands. Among several time periods of SPI index, three months period had a high correlation and therefore all calculations were computed based on the mentioned three months. The results showed that, in all stations of study area, both indices were high during spring months of March to May and decreased during the summer warm months. Both of the indices were high over the rich range lands and lower in poor range lands of province. The correlation between the indices was acceptable in all stations and this reveals that the use of the NDVI index instead of SPI is appropriate surrogate index in analyzing and monitoring droughts in Esfahan Provinc. The performance of mentioned indexes is high especially where the climatic data are rare and sparse and where time series are not regular.